Biogen Inc. (BIIB) Ownership
BIIB ownership summary
as of October 18, 2026- Institutions
- 99.6% of shares outstanding
- Insiders
- 0.19% of shares outstanding
- Shares outstanding
- 147.8M
- Float
- 147.2M shares available to trade
- Short interest
- 4.50% 6.0M shares short
- Days to cover
- 5.89 short interest up 2.5% vs prior month
- Institutions 99.63%
- Insiders 0.19%
- Other investors 0.18%
BIIB top institutional holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | FMR Inc | 12.33% | 18.2M | $4.24B | +5.4M (+42.2%) | June 30, 2026 |
| 2 | BlackRock Inc | 10.82% | 16.0M | $3.72B | +11,135 (+0.1%) | June 30, 2026 |
| 3 | PRIMECAP Management Company | 10.26% | 15.2M | $3.53B | +396,999 (+2.7%) | June 30, 2026 |
| 4 | Vanguard Capital Management, LLC | 6.53% | 9.7M | $2.25B | +113,700 (+1.2%) | June 30, 2026 |
| 5 | State Street Corp | 4.97% | 7.3M | $1.71B | +176,405 (+2.5%) | June 30, 2026 |
| 6 | Vanguard Portfolio Management, LLC | 4.47% | 6.6M | $1.54B | +73,209 (+1.1%) | June 30, 2026 |
| 7 | Geode Capital Management, LLC | 3.01% | 4.4M | $1.04B | +106,693 (+2.5%) | June 30, 2026 |
| 8 | Wellington Management Company LLP | 2.11% | 3.1M | $725.3M | +155,828 (+5.3%) | June 30, 2026 |
| 9 | NORGES BANK | 1.75% | 2.6M | $600.2M | −58,801 (−2.2%) | June 30, 2026 |
| 10 | Morgan Stanley - Brokerage Accounts | 1.63% | 2.4M | $561.0M | +240,331 (+11.1%) | June 30, 2026 |
| 11 | AQR Capital Management LLC | 1.31% | 1.9M | $450.6M | +13,302 (+0.7%) | June 30, 2026 |
| 12 | JPMorgan Chase & Co | 1.23% | 1.8M | $424.2M | −192,869 (−9.6%) | June 30, 2026 |
| 13 | Amvescap Plc. | 1.22% | 1.8M | $419.7M | +58,689 (+3.4%) | June 30, 2026 |
| 14 | Amundi | 1.03% | 1.5M | $352.9M | +726,004 (+91.8%) | June 30, 2026 |
| 15 | Legal & General Group PLC | 1.01% | 1.5M | $347.4M | +143,457 (+10.6%) | June 30, 2026 |
| 16 | Northern Trust Corp | 0.97% | 1.4M | $332.6M | −17,089 (−1.2%) | June 30, 2026 |
| 17 | Boston Partners Global Investors, Inc | 0.86% | 1.3M | $293.9M | −436,649 (−25.7%) | June 30, 2026 |
| 18 | UBS Asset Mgmt Americas Inc | 0.85% | 1.3M | $292.0M | −122,400 (−8.9%) | June 30, 2026 |
| 19 | The Goldman Sachs Group Inc | 0.83% | 1.2M | $286.3M | +179,296 (+17.1%) | June 30, 2026 |
| 20 | Dimensional Fund Advisors, Inc. | 0.78% | 1.1M | $267.2M | +69,449 (+6.4%) | June 30, 2026 |
Value at the latest close. Change = shares bought or sold in the latest quarterly filing (13F). In the top 20, 15 holders added 7.9M shares and 5 cut 828K.
BIIB top mutual fund and ETF holders
20 largest| # | Holder | % of shares | Shares | Value | Change | Reported |
|---|---|---|---|---|---|---|
| 1 | Vanguard PRIMECAP Inv | 5.66% | 8.4M | $1.94B | — | June 30, 2026 |
| 2 | Fidelity Contrafund | 3.26% | 4.8M | $1.12B | −167,284 (−3.4%) | August 31, 2026 |
| 3 | Vanguard MStar Total Stk Mkt Idx Invest | 3.18% | 4.7M | $1.09B | −8,972 (−0.2%) | August 31, 2026 |
| 4 | Vanguard 500 Index Investor | 2.63% | 3.9M | $903.1M | −41,808 (−1.1%) | September 30, 2026 |
| 5 | Vanguard MStar Mid Cap Index Instl | 2.14% | 3.2M | $736.1M | −29,547 (−0.9%) | September 30, 2026 |
| 6 | Vanguard Capital Opportunity Inv | 1.78% | 2.6M | $610.5M | +291,750 (+12.5%) | June 30, 2026 |
| 7 | Vanguard Health Care Inv | 1.71% | 2.5M | $587.7M | +123,446 (+5.1%) | June 30, 2026 |
| 8 | Fidelity Canadian Large Cp Mlt Ast Bs O | 1.56% | 2.3M | $536.9M | — | June 30, 2026 |
| 9 | iShares Core S&P 500 ETF | 1.33% | 2.0M | $458.4M | −3,182 (−0.2%) | September 30, 2026 |
| 10 | Fidelity 500 Index | 1.30% | 1.9M | $445.9M | +7,360 (+0.4%) | August 31, 2026 |
| 11 | State Street® SPDR® S&P 500® ETF | 1.23% | 1.8M | $423.3M | — | September 30, 2026 |
| 12 | Strategic Advisers Fidelity US TtlStk | 1.10% | 1.6M | $379.2M | +1,453 (+0.1%) | August 31, 2026 |
| 13 | Vanguard MStar Value Index Investor | 0.95% | 1.4M | $327.5M | −2,324 (−0.2%) | September 30, 2026 |
| 14 | Vanguard PRIMECAP Core Inv | 0.89% | 1.3M | $306.4M | — | June 30, 2026 |
| 15 | iShares Biotechnology ETF | 0.77% | 1.1M | $266.2M | −8,664 (−0.8%) | September 30, 2026 |
| 16 | State Street®HlthCrSelSectSPDR®ETF | 0.71% | 1.0M | $243.8M | +3,264 (+0.3%) | September 30, 2026 |
| 17 | Fidelity Contrafund K6 | 0.70% | 1.0M | $241.1M | −39,316 (−3.7%) | August 31, 2026 |
| 18 | Invesco S&P 500® Equal Weight ETF | 0.63% | 928K | $216.0M | −1,900 (−0.2%) | September 30, 2026 |
| 19 | Vanguard MStar Mid Cap Value ETF | 0.62% | 922K | $214.6M | −33,318 (−3.5%) | September 30, 2026 |
| 20 | Vanguard Institutional Index I | 0.53% | 781K | $181.7M | −8,713 (−1.1%) | September 30, 2026 |
Funds report holdings monthly or quarterly; dates differ by fund.
BIIB insider transactions
latest 9| Date | Name | Transaction | Price | Shares | Value |
|---|---|---|---|---|---|
| 2026-02-12 | Nicole Murphy | Buy | $195.03 | 3 | $585 |
| 2026-02-09 | Priya Singhal | Sell | $199.83 | 2,660 | $531,548 |
| 2026-02-06 | Ro Khanna | Sell | $201.18 | — | — |
| 2026-02-02 | Priya Singhal | Sell | $179.30 | 748 | $134,116 |
| 2026-01-30 | Gilbert Ray Cisneros, Jr. | Buy | $179.89 | — | — |
| 2026-01-29 | Ro Khanna | Buy | $176.18 | — | — |
| 2025-09-02 | Priya Singhal | Sell | $133.55 | 517 | $69,045 |
| 2025-08-26 | Ro Khanna | Buy | $136.72 | — | — |
| 2025-07-08 | Rachid Izzar | Sell | $135.00 | 2,223 | $300,105 |
Reported trades by company officers, directors and other filers (including disclosures by members of Congress where EODHD lists them). "—" where the filing gives no share count.
BIIB shares outstanding
Year-end shares outstanding, adjusted for splits.
Who owns BIIB
Institutional investors own 99.6% of Biogen's shares and insiders 0.19%. The largest holder is FMR Inc with 12.33% of the shares (18.2M), as of June 30, 2026. Among the top 20 institutions, 15 added shares and 5 reduced their stake in the latest filings. Short interest is 4.50% of the float, or 5.89 days of average trading volume. The share count fell 37.9% since 2014.
Related: BIIB analyst forecast, BIIB key metrics. See the BIIB stock overview for the latest quote and news.
BIIB ownership FAQ
Who owns the most Biogen stock?
The largest shareholders of Biogen are FMR Inc (12.33%), BlackRock Inc (10.82%), PRIMECAP Management Company (10.26%), Vanguard Capital Management, LLC (6.53%), State Street Corp (4.97%).
What percentage of Biogen is owned by institutions?
Institutions hold 99.6% of Biogen's shares outstanding; insiders hold 0.19%.
Which funds own Biogen?
The largest fund holders of Biogen are Vanguard PRIMECAP Inv (5.66%), Fidelity Contrafund (3.26%), Vanguard MStar Total Stk Mkt Idx Invest (3.18%), Vanguard 500 Index Investor (2.63%), Vanguard MStar Mid Cap Index Instl (2.14%).
What is Biogen's short interest?
6.0M shares of Biogen were sold short, 4.50% of the float; at the average daily volume it would take 5.89 days to cover.
Are insiders buying or selling Biogen?
Of the latest 9 reported insider transactions in Biogen (since July 8, 2025), 4 were purchases and 5 were sales.
How many shares of Biogen are outstanding?
Biogen has 147.8M shares outstanding, of which 147.2M are in the public float.