13D Filing: Kim D Blickenstaff and Tandem Diabetes Care Inc (NASDAQ:TNDM)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE
13D/A

Under the Securities Exchange Act of 1934

(Amendment No. 2)*

Tandem
Diabetes Care, Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

875372 104

(CUSIP
Number)

Kim D. Blickenstaff

President and Chief Executive Officer

Tandem Diabetes Care, Inc.

11045 Roselle Street

San
Diego, California 92121

(858) 366-6900

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

March 28, 2017

(Date of
Event Which Requires Filing of this Statement)

If the filing
person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box.  ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See
section 240.13d-7 for other parties to whom copies are to be sent.

*	The remainder of this cover page shall be filled out for a persons initial filing on this form with respect to subject class of securities, and for any subsequent amendment containing information which would alter disclosures in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be
filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the
Notes).