TNDM

EX-99.1

2 ex991-q3earningsrelease2026.htm

EX-99.1

Document

Exhibit 99.1

Media Contact:

858-366-6900

media@tandemdiabetes.com

Investor Contact:

858-366-6900

IR@tandemdiabetes.com

FOR IMMEDIATE RELEASE

Tandem Diabetes Care Announces Third Quarter 2026 Financial Results

San Diego, November 5, 2026 - Tandem Diabetes Care, Inc. (Nasdaq: TNDM) (the Company), a global insulin delivery and diabetes technology company, today reported its financial results for the quarter ended September 30, 2026.

Third Quarter 2026 Financial Highlights

•Sales of $283.7 million worldwide, including $191.0 million in the United States (U.S.)

•Gross margin of 57%, up 270 basis points compared to third quarter 2025

•Pump shipments of approximately 33,000 worldwide, including nearly 23,000 pumps in the U.S.

•Operating margin improved 830 basis points compared to third quarter 2025

•Scaled pay-as-you-go reimbursement model resulting in 15% of U.S. sales through the pharmacy channel

Third Quarter 2026 and Recent Strategic Highlights

•Increased pharmacy formulary coverage to approximately 50% of U.S. lives

•Expanded availability of t:slim X2 compatibility with the Abbott FreeStyle Libre 3 Plus Sensor to 11 international markets

•Announced international availability of Tandem Mobi in 12 countries

“Tandem’s third-quarter performance demonstrates that our strategy is delivering results,” said John Sheridan, president and chief executive officer. “We are expanding access to Tandem’s life-changing technology, strengthening our business model, advancing our pipeline and driving greater operating efficiency, creating a stronger foundation for sustainable, profitable growth.”

1

Exhibit 99.1

Third Quarter 2026 Financial Results Compared to Third Quarter 2025

•Sales: Worldwide sales increased 14% to $283.7 million, compared to $249.3 million on a reported basis and in constant currency(1).

Sales in the U.S. increased 9% to $191.0 million, compared to $175.6 million.

International sales increased 26% to $92.6 million, compared to $73.6 million. International sales increased 27% in constant currency(1).

Shipments in the U.S. were nearly 23,000 pumps, compared to more than 20,000 pumps.

International shipments were nearly 11,000 pumps, compared to more than 9,000 pumps.

•Gross profit: Gross profit was $160.4 million, compared to $134.3 million. Gross margin was 57%, compared to 54%.

•Operating loss: Operating loss was $2.4 million, or negative 1% of sales, compared to operating loss of $22.9 million, or negative 9% of sales.

•Net loss: Net loss was $7.1 million, compared to net loss of $21.2 million.

Adjusted EBITDA(1) was $18.0 million, or 6% of sales, compared to $2.8 million, or 1% of sales.

See tables for additional financial information.

2026 Financial Guidance

For the year ending December 31, 2026, the Company is reaffirming the following financial guidance:

•Sales are estimated to be approximately $1.065 billion to $1.085 billion

•U.S. sales of approximately $730 million to $745 million

•International sales of approximately $335 million to $340 million

•Gross margin is estimated to be approximately 56% to 57% of sales

•Adjusted EBITDA margin(2) is estimated to be approximately 5% to 6% of sales

•Non-cash charges included in cost of goods sold and operating expenses are estimated to be approximately $85 million. This includes:

•Approximately $65 million non-cash, stock-based compensation expense

•Approximately $20 million depreciation and amortization expense

For a comprehensive overview of the Company's guidance assumptions for 2026, including pricing and transition assumptions for the adoption of pay-as-you-go reimbursement in the U.S. and the initiation of international direct operations, please see the Events & Presentations tab in the Investor Center of the Tandem Diabetes Care website at https://investor.tandemdiabetes.com.

(1)Constant currency sales growth and adjusted EBITDA are non-GAAP financial measures. See “Non-GAAP Financial Measures” below for additional information on these non-GAAP financial measures. A reconciliation of constant currency to GAAP sales can be found in Table C “Sales by Geography and Non-GAAP Reconciliation of Constant Currency Sales Growth” attached to this press release. A reconciliation of adjusted EBITDA to net loss can be found in Table D “Reconciliation of GAAP versus Non-GAAP Financial Results” attached to this press release.

(2)Adjusted EBITDA margin is a non-GAAP financial measure. The Company has not reconciled adjusted EBITDA margin outlook to the most comparable GAAP outlook because it is not possible to do so without unreasonable efforts due to the uncertainty and potential variability of reconciling items, which are dependent on future events and often outside of management’s control and which could be significant. Because such items cannot reasonably be predicted with the level of precision required, the Company is unable to provide outlook for the comp

EX-99.1

2 ex991-q2earningsrelease2026.htm

EX-99.1

Document

Exhibit 99.1

Media Contact:

858-366-6900

media@tandemdiabetes.com

Investor Contact:

858-366-6900

IR@tandemdiabetes.com

FOR IMMEDIATE RELEASE

Tandem Diabetes Care Announces Second Quarter 2026 Financial Results

San Diego, August 6, 2026 - Tandem Diabetes Care, Inc. (Nasdaq: TNDM) (the Company), a global insulin delivery and diabetes technology company, today reported its financial results for the quarter ended June 30, 2026.

Second Quarter 2026 Financial Highlights

•Sales of $254.6 million worldwide, including $179.3 million in the United States (U.S.)

•Gross margin of 57%, up 460 basis points compared to second quarter 2025

•Pump shipments of more than 33,000 pumps worldwide, including 22,000 pumps in the U.S.

•Operating margin improved 800 basis points compared to second quarter 2025

•Scaled pay-as-you-go reimbursement model resulting in 10% of U.S. sales through the pharmacy channel

Second Quarter 2026 Strategic Highlights

•Submitted 510(k) with the U.S. Food and Drug Administration (FDA) for Tandem Mobi tubeless capability

•Expanded global portfolio of diabetes technology solutions

◦Received FDA clearance and CE Mark for the use of Control-IQ+ automated insulin delivery technology by people with type 1 diabetes during pregnancy, and received CE Mark for use by adults with type 2 diabetes

◦Introduced compatibility with the Dexcom G7 15-day sensor for both t:slim X2 and Tandem Mobi in the U.S.

◦Launched t:slim X2 compatibility with the Abbott FreeStyle Libre 3 Plus Sensor in four European markets

◦Began the international commercial rollout for Tandem Mobi

“Our second quarter results reflect meaningful progress across the priorities we set for 2026,” said John Sheridan, president and chief executive officer. “We are seeing tangible evidence that our strategy is gaining traction and the momentum we are building reinforces our confidence in Tandem’s ability to drive broader customer impact, strengthen our financial performance and create long-term value.”

1

Exhibit 99.1

Second Quarter 2026 Financial Results Compared to Second Quarter 2025

•Sales: Worldwide sales increased 6% to $254.6 million, compared to $240.7 million. Sales increased 5% in constant currency(1).

Sales in the U.S. increased 5% to $179.3 million, compared to $170.2 million.

International sales increased 7% to $75.3 million, compared to $70.5 million. International sales increased 6% in constant currency(1).

Shipments in the U.S. were more than 22,000 pumps, compared to approximately 21,000 pumps.

International shipments were approximately 11,000 pumps, compared to approximately 9,000 pumps.

•Gross profit: Gross profit was $144.8 million, compared to $125.9 million. Gross margin was 57%, compared to 52%.

•Operating loss: GAAP and non-GAAP operating loss(1) was $13.8 million, or negative 5% of sales, compared to GAAP operating loss of $51.8 million, or negative 22% of sales and non-GAAP operating loss(1) of $31.9 million, or negative 13% of sales, in the second quarter 2025. The second quarter 2025 included a $20.0 million charge for litigation settlement expense.

•Net income (loss): GAAP and non-GAAP net loss(1) was $21.2 million, compared to GAAP net loss of $52.4 million and non-GAAP net loss(1) of $32.4 million in the second quarter 2025.

Adjusted EBITDA(1) was $6.4 million, or 3% of sales, compared to negative $1.8 million, or negative 1% of sales.

See tables for additional financial information.

2026 Financial Guidance

For the year ending December 31, 2026, the Company is reaffirming the following financial guidance:

•Sales are estimated to be approximately $1.065 billion to $1.085 billion

•U.S. sales of approximately $730 million to $745 million

•International sales of approximately $335 million to $340 million

•Gross margin is estimated to be approximately 56% to 57% of sales

•Adjusted EBITDA margin(2) is estimated to be approximately 5% to 6% of sales

For the year ending December 31, 2026, the Company is updating its non-cash financial guidance as follows:

•Non-cash charges included in cost of goods sold and operating expenses are estimated to be approximately $85 million, a reduction from $100 million. This includes:

•Approximately $65 million non-cash, stock-based compensation expense, a reduction from $80 million

•Approximately $20 million depreciation and amortization expense

For a comprehensive overview of the Company's guidance assumptions for 2026, including pricing and transition assumptions for the adoption of pay-as-you go reimbursement in the U.S. and the initiation of international direct operations, please see the Events & Presentations tab in the Investor Center of the Tandem Diabetes Care website at https://investor.tandemdiabetes.com.

(1)Adjusted EBITDA, constant currency sales growth, non-GAAP operating loss, and non-GAAP net loss are non-GAAP financial measures. See “Non-GAAP Financial Measures” below for addi

EX-99.1

2 ex991-q1earningsrelease2026.htm

EX-99.1

Document

Exhibit 99.1

Media Contact:

858-366-6900

media@tandemdiabetes.com

Investor Contact:

858-366-6900

IR@tandemdiabetes.com

FOR IMMEDIATE RELEASE

Tandem Diabetes Care Announces First Quarter 2026 Financial Results

San Diego, May 7, 2026 - Tandem Diabetes Care, Inc. (Nasdaq: TNDM), a global insulin delivery and diabetes technology company, today reported its financial results for the quarter ended March 31, 2026 and reaffirmed financial guidance for the year ending December 31, 2026.

First Quarter 2026 Financial and Strategic Highlights

•Achieved record first quarter pump shipments, sales and gross margin:

◦Shipments of more than 29,000 pumps worldwide, including 19,000 pumps in the United States

◦Sales of $247.2 million worldwide, including $160.8 million in the United States

◦Gross margin of 55%, up 480 basis points compared to first quarter 2025

•Launched pay-as-you-go reimbursement model in the United States pharmacy channel

•Expanded Tandem Mobi connected care ecosystem by adding Android compatibility

•Demonstrated positive free cash flow and further reinforced balance sheet by closing a 0.00% convertible debt offering

“In the first quarter, we delivered on our financial plan while initiating key operational steps to advance our strategic priorities,” said John Sheridan, president and chief executive officer. “Our 2026 goals are firmly in focus, and we are committed to providing innovative, best-in-class diabetes technology to our customers in more efficient and cost-effective ways, while strengthening our global business model and building long-term value for shareholders.”

First Quarter 2026 Financial Results Compared to First Quarter 2025

•Sales: Worldwide sales increased 5% to $247.2 million, compared to $234.4 million. Sales increased 2% in constant currency(1).

Sales in the United States increased 7% to $160.8 million, compared to $150.6 million.

International sales increased 3% to $86.4 million compared to $83.8 million. Sales decreased 5% in constant currency(1).

Shipments in the United States were more than 19,000 pumps. International shipments were more than 10,000 pumps.

•Gross profit: Gross profit was $136.8 million, compared to $118.4 million. Gross margin was 55%, compared to 51%.

1

Exhibit 99.1

•Operating loss: GAAP and non-GAAP operating loss(2) was $17.4 million, or negative 7% of sales, compared to GAAP operating loss of $120.9 million, or negative 52% of sales and non-GAAP operating loss(2) of $109.7 million or negative 47% of sales, in the first quarter of 2025. The first quarter 2025 included a $75.2 million charge for acquired in-process research and development expenses (“IPR&D”).

•Net income (loss): GAAP and non-GAAP net loss(2) was $20.4 million, compared to GAAP net loss of $130.6 million and non-GAAP net loss(2) of $119.4 million, in the first quarter 2025.

Adjusted EBITDA(2) was $2.7 million, or 1% of sales, compared to negative $79.9 million, or negative 34% of sales.

(1) Constant currency sales growth is a non-GAAP measure that represents the change in sales between current and prior year periods using the exchange rate in effect during the applicable prior year period. The Company presents constant currency growth because management believes it provides meaningful information regarding the Company’s results on a consistent and comparable basis. The Company uses this non-GAAP measure to evaluate operating results. A reconciliation of constant currency to GAAP sales can be found in Table C “Sales by Geography and Non-GAAP Reconciliation of Constant Currency Sales Growth” attached to this press release. Also see “Non-GAAP Financial Measures” below for additional information.

(2) A reconciliation of non-GAAP financial measures to their most directly comparable GAAP financial measures and additional information can be found in Table D “Reconciliation of GAAP versus Non-GAAP Financial Results” attached to this press release. Also see “Non-GAAP Financial Measures” below for additional information.

See tables for additional financial information.

2026 Financial Guidance

For the year ending December 31, 2026, the Company is reaffirming its financial guidance as follows:

•Sales are estimated to be approximately $1.065 billion to $1.085 billion

•United States sales of approximately $730 million to $745 million

•International sales of approximately $335 million to $340 million

•Gross margin is estimated to be approximately 56% to 57% of sales

•Adjusted EBITDA(3) margin is estimated to be approximately 5% to 6% of sales

•Non-cash charges included in cost of goods sold and operating expenses are estimated to be approximately $100 million. This includes:

•Approximately $80 million non-cash, stock-based compensation expense

•Approximately $20 million depreciation and amortization expense

For a comprehensive overview of the Company's guidance assumptions for 2026, including pricing and transi

tndm-202602190001438133FALSE00014381332026-02-192026-02-19

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 19, 2026

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On February 19, 2026, we issued a press release reporting our financial results for the quarter and year ended December 31, 2025. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated February 19, 2026.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: February 19, 2026 3

tndm-202511060001438133FALSE00014381332025-11-062025-11-06

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 6, 2025

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On November 6, 2025, we issued a press release reporting our financial results for the quarter ended September 30, 2025. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated September 30, 2025.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: November 6, 2025 3

tndm-202508060001438133FALSE00014381332025-04-302025-04-30

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 6, 2025

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On June 30, 2025, we issued a press release reporting our financial results for the quarter ended June 30, 2025. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated June 30, 2025.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: August 6, 2025 3

tndm-202504300001438133FALSE00014381332025-04-302025-04-30

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April 30, 2025

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On April 30, 2025, we issued a press release reporting our financial results for the quarter ended March 31, 2025. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated April 30, 2025.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: April 30, 2025 3

tndm-202502260001438133FALSE00014381332025-02-262025-02-26

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 26, 2025

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On February 26, 2025, we issued a press release reporting our financial results for the quarter and year ended December 31, 2024. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated February 26, 2025.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: February 26, 2025 3

tndm-202411060001438133FALSE00014381332024-11-062024-11-06

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 6, 2024

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On November 6, 2024, we issued a press release reporting our financial results for the quarter ended September 30, 2024. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated November 6, 2024.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: November 6, 2024 3

tndm-202408010001438133FALSE00014381332024-08-012024-08-01

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 1, 2024

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On August 1, 2024, we issued a press release reporting our financial results for the quarter ended June 30, 2024. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated August 1, 2024.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Executive Vice President, Chief Legal, Privacy & Compliance Officer and Secretary

Date: August 1, 2024 3

tndm-202405020001438133FALSE00014381332024-05-022024-05-02

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 2, 2024

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On May 2, 2024, we issued a press release reporting our financial results for the quarter ended March 31, 2024. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated May 2, 2024.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Chief Legal, Privacy & Compliance Officer; Secretary

Date: May 2, 2024 3

tndm-202402210001438133FALSE00014381332024-02-212024-02-21

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 21, 2024

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On February 21, 2024, we issued a press release reporting our financial results for the quarter and year ended December 31, 2023. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated February 21, 2024.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Chief Legal, Privacy & Compliance Officer; Secretary

Date: February 21, 2024 3

tndm-202311010001438133FALSE00014381332023-11-012023-11-01

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 1, 2023

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On November 1, 2023, we issued a press release reporting our financial results for the quarter ended September 30, 2023. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated November 1, 2023.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Chief Legal, Privacy & Compliance Officer; Secretary

Date: November 1, 2023 3

tndm-202308030001438133FALSE00014381332023-08-032023-08-03

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 3, 2023

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On August 3, 2023, we issued a press release reporting our financial results for the quarter ended June 30, 2023. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated August 3, 2023.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Senior Vice President, General Counsel, Corporate Secretary & Chief Compliance Officer

Date: August 3, 2023 3

tndm-202305030001438133FALSE00014381332023-05-032023-05-03

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 3, 2023

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 12400 High Bluff Drive92130 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On May 3, 2023, we issued a press release reporting our financial results for the quarter ended March 31, 2023. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated May 3, 2023.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Senior Vice President, General Counsel, Corporate Secretary & Chief Compliance Officer

Date: May 3, 2023 3

tndm-202302170001438133FALSE00014381332023-02-172023-02-17

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): February 17, 2023

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 11075 Roselle Street92121 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On February 22, 2023, we issued a press release reporting our financial results for the quarter and year ended December 31, 2022. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On February 22, 2023, the Company issued a press release announcing that Rebecca Robertson will succeed Kim D. Blickenstaff as Chair of the Board of Directors (the “Board”), effective March 1, 2023. Mr. Blickenstaff will continue as a member of the Board.

This press release has been furnished as Exhibit 99.2 to this report and is incorporated herein by this reference. This press release is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any filing under the Securities Act or the Exchange Act, except as expressly set forth by specific reference in such filing.

Appointment of Chair of the Board

On February 22, 2023, the following appointments were approved by the Board, effective March 1, 2023:

•Mr. Blickenstaff will transition from the role of Chair of the Board to a member of the Board, where he has served as one of the Company’s directors since September 2007. Mr. Blickenstaff served as Chair since March 2020, and Executive Chairman from March 2019 - March 2020. Mr. Blickenstaff was the Company’s President and Chief Executive Officer from September 2007 to February 2019,

•Ms. Robertson will transition to the role of Chair. Ms. Robertson has served as a member of the Board since January 2019.

Ms. Robertson, age 62, has extensive experience helping medical device companies scale in her roles as an engineer, entrepreneur, corporate executive and board member. She is a founder and General Partner at Versant Ventures where she has specialized in investing in the areas of medical devices and diagnostics since 1999. In addition, through Longridge Business Advisors, she has provided business advisory services and board services since April 2017. Prior to V

tndm-202301100001438133FALSE00014381332023-01-102023-01-10

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): January 10, 2023

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 11075 Roselle Street92121 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNasdaq Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On January 10, 2023, the Company issued a press release announcing its unaudited, preliminary financial results for the quarter and full year ended December 31, 2022, as well as its preliminary financial guidance for the full year ending December 31, 2023. A copy of the press release is attached as Exhibit 99.1 to this Current Report on Form 8-K.

The 2022 unaudited financial results contained in the press release are preliminary and subject to adjustment. The final, audited financial results will be included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 to be filed with the Securities and Exchange Commission.

The information provided under this Item 2.02, including Exhibit 99.1 hereto, is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d) Exhibits.

Number  Description 99.1Press release of Tandem Diabetes Care, Inc. dated January 10, 2023

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ Leigh A. Vosseller

Leigh A. Vosseller Executive Vice President, Chief Financial Officer and Treasurer

Date: January 9, 2023 3

tndm-202211020001438133FALSE00014381332022-11-022022-11-02

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 2, 2022

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 11075 Roselle Street92121 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On November 2, 2022, we issued a press release reporting our financial results for the quarter ended September 30, 2022. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated November 2, 2022.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Senior Vice President, General Counsel, Corporate Secretary & Chief Compliance Officer

Date: November 2, 2022 3

tndm-202208030001438133FALSE00014381332022-08-032022-08-03

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): August 3, 2022

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 11075 Roselle Street92121 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On August 3, 2022, we issued a press release reporting our financial results for the quarter ended June 30, 2022. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated August 3, 2022.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Senior Vice President, General Counsel, Corporate Secretary & Chief Compliance Officer

Date: August 3, 2022 3

tndm-202205040001438133FALSE00014381332022-05-042022-05-04

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): May 4, 2022

Tandem Diabetes Care, Inc. (Exact name of registrant as specified in its charter)

Delaware001-3618920-4327508 (State or other jurisdiction of incorporation)(Commission File Number)(I.R.S. Employer Identification No.) 11075 Roselle Street92121 San Diego California (Zip Code) (Address of principal executive offices)

Registrant’s telephone number, including area code: (858) 366-6900 N/A (Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act: Title of Each ClassTrading SymbolName of Each Exchange on Which Registered Common Stock, par value $0.001 per shareTNDMNASDAQ Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 2.02 Results of Operations and Financial Condition.

On May 4, 2022, we issued a press release reporting our financial results for the quarter ended March 31, 2022. This press release has been furnished as Exhibit 99.1 to this report and is incorporated herein by this reference.

The information under this Item 2.02 and Exhibit 99.1 hereto is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or the Exchange Act, or otherwise subject to the liabilities of that section, nor shall they be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits. (d)     Exhibits.

Number Description

99.1Press release of Tandem Diabetes Care, Inc. dated May 4, 2022.

104Cover Page Interactive Data File (embedded within the Inline XBRL document).

2

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Tandem Diabetes Care, Inc.

By:/s/ SHANNON M. HANSEN Shannon M. Hansen Senior Vice President & General Counsel

Date: May 4, 2022 3