Who owns Tandem Diabetes Care, Inc. (TNDM)
Which tracked institutional funds hold TNDM, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See TNDM company fundamentals →
Ownership as of the 2026-Q1 13F filings (latest filed 2026-05-18). 13F is disclosed up to 45 days after quarter-end, so the most recent quarter fills in over the following weeks.
How the tape is positioned
43 tracked funds added or opened TNDM while 80 trimmed or exited it between 2025-Q4 and 2026-Q1 — the tape is split. When large holders disagree on a name, the funds moving first are sometimes ahead of the story.
A prompt to read the filings, not a verdict. 13F is a quarter-end snapshot disclosed up to 45 days late; a fund adds or exits for mandate, benchmark, and timing reasons that have nothing to do with a view on the stock. This is a starting question, not a signal to trade.
Conviction spread
TNDM’s largest tracked holder by dollar value, VANGUARD GROUP INC, sizes it at 0.0% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 0.0pp gap the other way — the median holder sizes TNDM more heavily than its largest holder by dollar value does.
Book-share is each fund’s reported value in TNDM divided by its whole reported 13F book, so it is comparable across funds of different sizes and is unaffected by stock splits. A higher share means a fund has committed more of its book to the name — a starting question about conviction, not a verdict or a signal to trade.
Institutional & insider positioning
Between 2025-Q4 and 2026-Q1, across 274 tracked filers holding TNDM, 139 increased or opened the position and 135 reduced or closed it; over the same quarter, open-market insider Form 4 buying and selling roughly offset.
This fuses two public signals for the same quarter — how tracked institutions changed their positions and whether insiders bought or sold in the open market. It describes what was filed; it is a starting question, not a verdict or a signal to trade.
New buyers & exits
Funds opening or closing a position in TNDM between the 2025-Q4 and 2026-Q1 13F filings, and the largest changes among funds holding it in both. New buyers and exits are counted on fund presence (split-invariant); adds and trims are measured on reported value.
New buyers 20
- VANGUARD PORTFOLIO MANAGEMENT LLC$77M
- VANGUARD CAPITAL MANAGEMENT LLC$58M
- Soleus Capital Management, L.P.$15M
- Defilade Capital Management, L.P.$15M
- ExodusPoint Capital Management, LP$12M
- VANGUARD FIDUCIARY TRUST CO$9M
Full exits 14
- VANGUARD GROUP INC$149M
- TWO SIGMA ADVISERS, LP$21M
- Balyasny Asset Management L.P.$6M
- JANE STREET GROUP, LLC$5M
- ADAGE CAPITAL PARTNERS GP, L.L.C.$4M
- Engineers Gate Manager LP$2M
Largest adds
- UBS Group AG$30M
- WELLINGTON MANAGEMENT GROUP LLP$16M
- TWO SIGMA INVESTMENTS, LP$9M
- Holocene Advisors, LP$9M
- Driehaus Capital Management LLC$9M
- MARSHALL WACE, LLP$8M
Largest trims
- BlackRock, Inc.$103M
- Assenagon Asset Management S.A.$24M
- BNP PARIBAS FINANCIAL MARKETS$23M
- MORGAN STANLEY$20M
- Sessa Capital IM, L.P.$19M
- JENNISON ASSOCIATES LLC$13M
Institutional holders
One row per tracked fund, largest reported value first. “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding. Rows marked stale are from an earlier filing than the security’s latest quarter — that fund is absent from the newest snapshot (position exited, or reported under a different name).
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| BlackRock, Inc. trimmed | 7,428,041 | $142M | 8.0% | 2026-Q1 |
| Sessa Capital IM, L.P. trimmed | 4,730,757 | $91M | 5.1% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 3,993,333 | $77M | 4.3% | 2026-Q1 |
| ArrowMark Colorado Holdings LLC added | 3,103,609 | $59M | 3.3% | 2026-Q1 |
| VANGUARD CAPITAL MANAGEMENT LLC new | 3,038,919 | $58M | 3.3% | 2026-Q1 |
| GW&K Investment Management, LLC added | 2,689,106 | $52M | 2.9% | 2026-Q1 |
| STATE STREET CORP added | 2,662,260 | $51M | 2.9% | 2026-Q1 |
| Driehaus Capital Management LLC added | 2,304,414 | $44M | 2.5% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC added | 2,218,922 | $43M | 2.4% | 2026-Q1 |
| CITADEL ADVISORS LLC added | 2,192,667 | $42M | 2.4% | 2026-Q1 |
| UBS Group AG added | 2,047,801 | $39M | 2.2% | 2026-Q1 |
| Paradice Investment Management LLC trimmed | 2,042,425 | $39M | 2.2% | 2026-Q1 |
| TWO SIGMA INVESTMENTS, LP added | 1,864,194 | $36M | 2.0% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 1,679,863 | $32M | 1.8% | 2026-Q1 |
| JENNISON ASSOCIATES LLC trimmed | 1,658,448 | $32M | 1.8% | 2026-Q1 |
| JACOBS LEVY EQUITY MANAGEMENT, INC trimmed | 1,523,946 | $29M | 1.6% | 2026-Q1 |
| MARSHALL WACE, LLP added | 1,442,438 | $28M | 1.5% | 2026-Q1 |
| MORGAN STANLEY trimmed | 1,357,542 | $26M | 1.5% | 2026-Q1 |
| Freestone Grove Partners LP trimmed | 1,330,742 | $26M | 1.4% | 2026-Q1 |
| First Light Asset Management, LLC added | 1,314,715 | $25M | 1.4% | 2026-Q1 |
| BAILLIE GIFFORD & CO trimmed | 1,089,393 | $21M | 1.2% | 2026-Q1 |
| WELLINGTON MANAGEMENT GROUP LLP added | 931,505 | $18M | 1.0% | 2026-Q1 |
| VOYA INVESTMENT MANAGEMENT LLC added | 804,137 | $15M | 0.9% | 2026-Q1 |
| D. E. Shaw & Co., Inc. trimmed | 783,906 | $15M | 0.8% | 2026-Q1 |
| Soleus Capital Management, L.P. added | 783,000 | $15M | 0.8% | 2026-Q1 |
| Defilade Capital Management, L.P. new | 761,905 | $15M | 0.8% | 2026-Q1 |
| MILLENNIUM MANAGEMENT LLC added | 761,672 | $15M | 0.8% | 2026-Q1 |
| NORTHERN TRUST CORP added | 706,609 | $14M | 0.8% | 2026-Q1 |
| ROYCE & ASSOCIATES LP added | 696,590 | $13M | 0.7% | 2026-Q1 |
| Quantinno Capital Management LP added | 653,870 | $13M | 0.7% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 642,598 | $12M | 0.7% | 2026-Q1 |
| ExodusPoint Capital Management, LP added | 632,899 | $12M | 0.7% | 2026-Q1 |
| Holocene Advisors, LP added | 477,359 | $9M | 0.5% | 2026-Q1 |
| FMR LLC trimmed | 476,900 | $9M | 0.5% | 2026-Q1 |
| VANGUARD FIDUCIARY TRUST CO new | 471,658 | $9M | 0.5% | 2026-Q1 |
| Aberdeen Group plc trimmed | 434,027 | $8M | 0.5% | 2026-Q1 |
| BARCLAYS PLC trimmed | 421,236 | $8M | 0.5% | 2026-Q1 |
| Point72 Asset Management, L.P. trimmed | 420,478 | $8M | 0.5% | 2026-Q1 |
| FRONTIER CAPITAL MANAGEMENT CO LLC trimmed | 397,209 | $8M | 0.4% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ trimmed | 373,224 | $7M | 0.4% | 2026-Q1 |
| Nuveen, LLC trimmed | 363,802 | $7M | 0.4% | 2026-Q1 |
| JPMORGAN CHASE & CO added | 349,792 | $7M | 0.4% | 2026-Q1 |
| DAFNA Capital Management LLC | 355,208 | $7M | 0.4% | 2026-Q1 |
| FIRST TRUST ADVISORS LP added | 342,707 | $7M | 0.4% | 2026-Q1 |
| Bank of New York Mellon Corp trimmed | 336,291 | $6M | 0.4% | 2026-Q1 |
| PRINCIPAL FINANCIAL GROUP INC added | 331,541 | $6M | 0.4% | 2026-Q1 |
| AQR CAPITAL MANAGEMENT LLC trimmed | 319,327 | $6M | 0.3% | 2026-Q1 |
| Invesco Ltd. added | 294,052 | $6M | 0.3% | 2026-Q1 |
| ACADIAN ASSET MANAGEMENT LLC trimmed | 278,116 | $5M | 0.3% | 2026-Q1 |
| SECTOR GAMMA AS | 267,091 | $5M | 0.3% | 2026-Q1 |
| EDMOND DE ROTHSCHILD HOLDING S.A. | 258,200 | $5M | 0.3% | 2026-Q1 |
| BEACONLIGHT CAPITAL, LLC added | 253,877 | $5M | 0.3% | 2026-Q1 |
| Trexquant Investment LP added | 249,298 | $5M | 0.3% | 2026-Q1 |
| ENVESTNET ASSET MANAGEMENT INC added | 243,248 | $5M | 0.3% | 2026-Q1 |
| Public Sector Pension Investment Board added | 242,596 | $5M | 0.3% | 2026-Q1 |
| BNP PARIBAS FINANCIAL MARKETS trimmed | 208,713 | $4M | 0.2% | 2026-Q1 |
| Susquehanna Portfolio Strategies, LLC added | 206,193 | $4M | 0.2% | 2026-Q1 |
| ROYAL BANK OF CANADA trimmed | 206,033 | $4M | 0.2% | 2026-Q1 |
| ARROWSTREET CAPITAL, LIMITED PARTNERSHIP added | 193,556 | $4M | 0.2% | 2026-Q1 |
| RHUMBLINE ADVISERS added | 186,316 | $4M | 0.2% | 2026-Q1 |
| Assenagon Asset Management S.A. trimmed | 178,640 | $3M | 0.2% | 2026-Q1 |
| UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC added | 168,493 | $3M | 0.2% | 2026-Q1 |
| Lisanti Capital Growth, LLC trimmed | 165,325 | $3M | 0.2% | 2026-Q1 |
| PANAGORA ASSET MANAGEMENT INC added | 163,695 | $3M | 0.2% | 2026-Q1 |
| MIZUHO MARKETS AMERICAS LLC added | 157,362 | $3M | 0.2% | 2026-Q1 |
| Legal & General Group Plc trimmed | 155,288 | $3M | 0.2% | 2026-Q1 |
| TORONTO DOMINION BANK added | 150,078 | $3M | 0.2% | 2026-Q1 |
| Russell Investments Group, Ltd. added | 133,596 | $3M | 0.1% | 2026-Q1 |
| Swiss National Bank | 133,300 | $3M | 0.1% | 2026-Q1 |
| RAYMOND JAMES FINANCIAL INC added | 125,345 | $2M | 0.1% | 2026-Q1 |
| BANQUE PICTET & CIE SA added | 123,935 | $2M | 0.1% | 2026-Q1 |
| FEDERATED HERMES, INC. added | 123,819 | $2M | 0.1% | 2026-Q1 |
| AMERIPRISE FINANCIAL INC trimmed | 121,150 | $2M | 0.1% | 2026-Q1 |
| VANGUARD GROUP INC trimmed | 6,776,123 | $149M | 8.3% | 2025-Q4 stale |
| Stephens Investment Management Group LLC added | 1,737,769 | $32M | 1.8% | 2025-Q2 stale |
| Hood River Capital Management LLC trimmed | 2,551,644 | $31M | 1.7% | 2025-Q3 stale |
| Champlain Investment Partners, LLC added | 1,455,123 | $27M | 1.5% | 2025-Q2 stale |
| Ophir Asset Management Pty Ltd new | 1,464,956 | $24M | 1.4% | 2025-Q2 stale |
| Park West Asset Management LLC trimmed | 1,123,052 | $22M | 1.2% | 2025-Q1 stale |
| TWO SIGMA ADVISERS, LP trimmed | 937,983 | $21M | 1.2% | 2025-Q4 stale |
| BROWN ADVISORY INC added | 1,057,115 | $20M | 1.1% | 2025-Q2 stale |
| Capital World Investors | 767,000 | $14M | 0.8% | 2025-Q2 stale |
| FRED ALGER MANAGEMENT, LLC trimmed | 667,345 | $12M | 0.7% | 2025-Q2 stale |
| KINGDON CAPITAL MANAGEMENT, L.L.C. trimmed | 495,229 | $9M | 0.5% | 2025-Q1 stale |
| Connor, Clark & Lunn Investment Management Ltd. trimmed | 615,221 | $7M | 0.4% | 2025-Q3 stale |
| Silvercrest Asset Management Group LLC added | 346,160 | $6M | 0.4% | 2025-Q2 stale |
| Balyasny Asset Management L.P. added | 262,788 | $6M | 0.3% | 2025-Q4 stale |
| Walleye Capital LLC trimmed | 463,376 | $6M | 0.3% | 2025-Q3 stale |
| Cubist Systematic Strategies, LLC added | 439,158 | $5M | 0.3% | 2025-Q3 stale |
| JANE STREET GROUP, LLC trimmed | 209,975 | $5M | 0.3% | 2025-Q4 stale |
| BROWN CAPITAL MANAGEMENT LLC trimmed | 363,352 | $4M | 0.2% | 2025-Q3 stale |
| ADAGE CAPITAL PARTNERS GP, L.L.C. trimmed | 182,995 | $4M | 0.2% | 2025-Q4 stale |
| FIL Ltd trimmed | 191,417 | $4M | 0.2% | 2025-Q2 stale |
| 1492 Capital Management LLC added | 188,754 | $4M | 0.2% | 2025-Q2 stale |
| Squarepoint Ops LLC added | 180,660 | $3M | 0.2% | 2025-Q2 stale |
| iA Global Asset Management Inc. new | 165,380 | $3M | 0.2% | 2025-Q1 stale |
| Kent Lake PR LLC new | 250,000 | $3M | 0.2% | 2025-Q3 stale |
| Aquatic Capital Management LLC added | 162,030 | $3M | 0.2% | 2025-Q2 stale |
| Polar Capital Holdings Plc trimmed | 140,536 | $3M | 0.2% | 2025-Q1 stale |
| MOORE CAPITAL MANAGEMENT, LP added | 220,479 | $3M | 0.1% | 2025-Q3 stale |
Ownership over time
Tracked institutional holder count and total shares held by filing quarter (independent scales). The curated-era tail and any mid-ingest latest quarter are handled honestly — a partial quarter is not drawn as a collapse.
Reading this table
Funds hold the same stock for different reasons — an index fund “holds” almost everything, an active manager sizes a name to a mandate and a benchmark, and each fund entered at its own price and time. Because 13F is filed up to 45 days after quarter-end, every row is a backward-looking snapshot; a manager may have traded since. Share-class siblings (a company’s A and C shares) are rolled up to one line so a dual-class name is never double-counted. Compare like-for-like. A large holder is not an endorsement, and a fund exiting is not a warning — this is a starting question, not a verdict.
About 13F filings
A Form 13F is a quarterly disclosure that institutional investment managers with over $100 million in US-listed equities must file with the SEC. In plain English: it is a snapshot of the long stock positions a fund held at the end of a quarter. It covers long US-listed equities only — not short positions, options, cash, or private holdings — and the funds shown are the large sample we track, not the complete 13F universe.