Biogen Inc.
BIIB- Exchange
- Nasdaq
- Industry
- Biological Products, (No Diagnostic Substances)
- SEC CIK
- 0000875045
No open-market purchases or sales by Biogen Inc. insiders were filed in the last 90 days; 1,049 institutions reported holding it in 13F filings for Q2 2026, worth $30.7B in total; no superinvestor holds it.
Four kinds of short-selling data, each measuring something different:
- Short interest: shares sold short and not yet bought back, as of a settlement date. FINRA publishes it twice a month, about eight business days after the settlement date.
- Daily short volume: shares sold short each day in off-exchange trades reported to FINRA. It counts trades, not open positions, and is published the next day.
- Fails-to-deliver: shares not delivered by the settlement date. The SEC publishes them twice a month, about two weeks late.
- ATS (dark pool) volume: weekly volume on alternative trading systems and other off-exchange venues. FINRA publishes it two to four weeks after the week.
More in the glossary.
Short interest
Shares sold short and not yet bought back, from FINRA, on every settlement date in the last two years.
- Short interest
- 5.45M
- Shares, settlement Oct 30, 2026
- Change
- −47.3K
- −0.9% vs. Oct 15, 2026
- Days to cover
- 3.96
- Short interest ÷ average daily volume
- Average daily volume
- 1.38M
- Shares, as reported by FINRA
| Settlement date | Short interest | Change | Change % | Avg. daily volume | Days to cover |
|---|---|---|---|---|---|
| Oct 30, 2026 | 5.45M | −47.3K | −0.9% | 1.38M | 3.96 |
| Oct 15, 2026 | 5.50M | −465.5K | −7.8% | 1.25M | 4.39 |
| Sep 30, 2026 | 5.97M | +148.1K | +2.6% | 1.23M | 4.87 |
| Sep 15, 2026 | 5.82M | +91.2K | +1.6% | 766.5K | 7.59 |
| Aug 31, 2026 | 5.73M | +536.1K | +10.3% | 661.6K | 8.66 |
| Aug 14, 2026 | 5.19M | −263.3K | −4.8% | 847.1K | 6.13 |
| Jul 31, 2026 | 5.45M | −545.2K | −9.1% | 1.15M | 4.73 |
| Jul 15, 2026 | 6.00M | +275.9K | +4.8% | 1.74M | 3.45 |
| Jun 30, 2026 | 5.72M | +534.4K | +10.3% | 1.38M | 4.14 |
| Jun 15, 2026 | 5.19M | +417.3K | +8.8% | 918.7K | 5.65 |
| May 29, 2026 | 4.77M | +41.5K | +0.9% | 1.06M | 4.49 |
| May 15, 2026 | 4.73M | +254.5K | +5.7% | 1.12M | 4.21 |
| Apr 30, 2026 | 4.48M | +60.5K | +1.4% | 1.25M | 3.59 |
| Apr 15, 2026 | 4.41M | +588.5K | +15.4% | 1.44M | 3.07 |
| Mar 31, 2026 | 3.83M | −508.4K | −11.7% | 1.10M | 3.47 |
| Mar 13, 2026 | 4.33M | +131.9K | +3.1% | 842.1K | 5.15 |
| Feb 27, 2026 | 4.20M | −342.3K | −7.5% | 908.3K | 4.63 |
| Feb 13, 2026 | 4.55M | −147.5K | −3.1% | 1.85M | 2.45 |
| Jan 30, 2026 | 4.69M | +14.6K | +0.3% | 1.30M | 3.62 |
| Jan 15, 2026 | 4.68M | +211.7K | +4.7% | 1.78M | 2.62 |
| Dec 31, 2025 | 4.47M | −2.12M | −32.2% | 2.67M | 1.67 |
| Dec 15, 2025 | 6.59M | −186.5K | −2.8% | 1.80M | 3.67 |
| Nov 28, 2025 | 6.78M | +636.6K | +10.4% | 2.08M | 3.26 |
| Nov 14, 2025 | 6.14M | +496.2K | +8.8% | 1.92M | 3.19 |
| Oct 31, 2025 | 5.64M | +453.6K | +8.7% | 1.57M | 3.60 |
| Oct 15, 2025 | 5.19M | +311.0K | +6.4% | 1.93M | 2.69 |
| Sep 30, 2025 | 4.88M | −245.7K | −4.8% | 1.64M | 2.98 |
| Sep 15, 2025 | 5.13M | +404.8K | +8.6% | 1.70M | 3.01 |
| Aug 29, 2025 | 4.72M | +565.8K | +13.6% | 1.32M | 3.58 |
| Aug 15, 2025 | 4.16M | +195.5K | +4.9% | 1.55M | 2.68 |
| Jul 31, 2025 | 3.96M | +63.5K | +1.6% | 1.42M | 2.78 |
| Jul 15, 2025 | 3.90M | −104.5K | −2.6% | 1.20M | 3.23 |
| Jun 30, 2025 | 4.00M | +611.4K | +18.0% | 1.30M | 3.07 |
| Jun 13, 2025 | 3.39M | −406.0K | −10.7% | 1.32M | 2.57 |
| May 30, 2025 | 3.80M | +455.7K | +13.6% | 1.78M | 2.13 |
| May 15, 2025 | 3.34M | +155.3K | +4.9% | 1.73M | 1.93 |
| Apr 30, 2025 | 3.18M | −262.2K | −7.6% | 1.47M | 2.17 |
| Apr 15, 2025 | 3.45M | +102.6K | +3.1% | 2.05M | 1.68 |
| Mar 31, 2025 | 3.34M | +33.3K | +1.0% | 1.60M | 2.09 |
| Mar 14, 2025 | 3.31M | −409.4K | −11.0% | 1.91M | 1.73 |
| Feb 28, 2025 | 3.72M | −163.8K | −4.2% | 1.62M | 2.30 |
| Feb 14, 2025 | 3.88M | +142.6K | +3.8% | 1.65M | 2.35 |
| Jan 31, 2025 | 3.74M | −28.6K | −0.8% | 1.29M | 2.91 |
| Jan 15, 2025 | 3.77M | +93.1K | +2.5% | 1.25M | 3.01 |
| Dec 31, 2024 | 3.68M | +1.10M | +42.7% | 1.67M | 2.20 |
| Dec 13, 2024 | 2.58M | −146.2K | −5.4% | 1.33M | 1.94 |
| Nov 29, 2024 | 2.72M | +27.5K | +1.0% | 1.55M | 1.76 |
| Nov 15, 2024 | 2.70M | −425.2K | −13.6% | 1.85M | 1.46 |
| Oct 31, 2024 | 3.12M | +53.3K | +1.7% | 1.24M | 2.52 |
Fails-to-deliver
Shares that weren't delivered by the settlement date, from the SEC, for the last 30 dates with fails. The price is the previous day's closing price published by the SEC.
| Settlement date | Shares | Price | Value |
|---|---|---|---|
| Oct 14, 2026 | 2,091 | $228.90 | $478.6K |
| Oct 9, 2026 | 318 | $218.43 | $69.5K |
| Oct 6, 2026 | 3,117 | $223.59 | $696.9K |
| Oct 5, 2026 | 1,440 | $219.88 | $316.6K |
| Sep 28, 2026 | 49,163 | $227.60 | $11.2M |
| Sep 24, 2026 | 58 | $227.53 | $13.2K |
| Sep 23, 2026 | 300 | $225.36 | $67.6K |
| Sep 22, 2026 | 187 | $219.07 | $41.0K |
| Sep 21, 2026 | 61 | $215.50 | $13.1K |
| Sep 18, 2026 | 2,277 | $219.05 | $498.8K |
| Sep 17, 2026 | 634 | $216.01 | $137.0K |
| Sep 14, 2026 | 416 | $217.15 | $90.3K |
| Sep 11, 2026 | 386 | $215.43 | $83.2K |
| Sep 8, 2026 | 7,185 | $220.83 | $1.59M |
| Sep 4, 2026 | 17,209 | $224.51 | $3.86M |
| Sep 2, 2026 | 35 | $216.04 | $7.56K |
| Aug 28, 2026 | 991 | $221.50 | $219.5K |
| Aug 25, 2026 | 3,091 | $218.12 | $674.2K |
| Aug 24, 2026 | 93 | $216.78 | $20.2K |
| Aug 21, 2026 | 145 | $214.35 | $31.1K |
| Aug 7, 2026 | 135 | $206.28 | $27.8K |
| Aug 3, 2026 | 2,347 | $202.95 | $476.3K |
| Jul 17, 2026 | 8 | $208.92 | $1.67K |
| Jul 16, 2026 | 63 | $197.24 | $12.4K |
| Jun 30, 2026 | 2,785 | $216.63 | $603.3K |
| Jun 29, 2026 | 165 | $216.03 | $35.6K |
| Jun 25, 2026 | 215 | $199.59 | $42.9K |
| Jun 22, 2026 | 2,157 | $196.58 | $424.0K |
| Jun 15, 2026 | 692 | $200.05 | $138.4K |
| Jun 3, 2026 | 104 | $188.83 | $19.6K |
Daily short volume
Off-exchange short-sale volume, not short interest: shares sold short each day in trades reported to FINRA, for the last 30 trading days.
The short volume ratio isn't a sentiment gauge: market makers sell short to fill buy orders and to hedge, so short sales are usually about half of off-exchange volume.
| Trade date | Short volume | Short exempt | Off-exchange volume | Short volume ratio |
|---|---|---|---|---|
| Nov 11, 2026 | 233,554 | 1 | 435,036 | 53.7% |
| Nov 10, 2026 | 131,053 | 319 | 280,797 | 46.7% |
| Nov 9, 2026 | 268,208 | 2 | 472,569 | 56.8% |
| Nov 6, 2026 | 158,066 | 68 | 376,693 | 42.0% |
| Nov 5, 2026 | 209,033 | 20 | 381,541 | 54.8% |
| Nov 4, 2026 | 216,924 | 244 | 430,615 | 50.4% |
| Nov 3, 2026 | 225,103 | 761 | 450,606 | 50.0% |
| Nov 2, 2026 | 183,508 | 64 | 416,716 | 44.0% |
| Oct 30, 2026 | 328,340 | 709 | 572,114 | 57.4% |
| Oct 29, 2026 | 307,391 | 2 | 440,481 | 69.8% |
| Oct 28, 2026 | 544,819 | 79 | 978,089 | 55.7% |
| Oct 27, 2026 | 309,492 | 0 | 537,276 | 57.6% |
| Oct 26, 2026 | 257,701 | 0 | 352,964 | 73.0% |
| Oct 23, 2026 | 357,103 | 0 | 491,252 | 72.7% |
| Oct 22, 2026 | 769,191 | 201 | 1,029,993 | 74.7% |
| Oct 21, 2026 | 187,252 | 0 | 313,596 | 59.7% |
| Oct 20, 2026 | 446,578 | 0 | 635,170 | 70.3% |
| Oct 19, 2026 | 225,594 | 0 | 356,957 | 63.2% |
| Oct 16, 2026 | 423,756 | 0 | 546,778 | 77.5% |
| Oct 15, 2026 | 451,045 | 365 | 576,664 | 78.2% |
| Oct 14, 2026 | 452,487 | 0 | 670,781 | 67.5% |
| Oct 13, 2026 | 277,062 | 100 | 383,698 | 72.2% |
| Oct 12, 2026 | 354,549 | 239 | 690,332 | 51.4% |
| Oct 9, 2026 | 182,556 | 362 | 348,775 | 52.3% |
| Oct 8, 2026 | 218,666 | 0 | 478,221 | 45.7% |
| Oct 7, 2026 | 278,272 | 14 | 528,154 | 52.7% |
| Oct 6, 2026 | 298,059 | 0 | 425,703 | 70.0% |
| Oct 5, 2026 | 223,179 | 0 | 407,863 | 54.7% |
| Oct 2, 2026 | 202,352 | 0 | 303,895 | 66.6% |
| Oct 1, 2026 | 380,080 | 0 | 747,360 | 50.9% |
ATS (dark pool) volume
Weekly volume on alternative trading systems (ATS) and other off-exchange (OTC) venues, from FINRA, for the last 12 weeks. ATS share is ATS volume ÷ (ATS + OTC volume), not a share of all trading.
| Week of | Tier | ATS shares | ATS trades | Other OTC shares | Other OTC trades | ATS share |
|---|---|---|---|---|---|---|
| Oct 19, 2026 | T1 | 1,977,775 | 52,689 | 970,406 | 26,677 | 67.1% |
| Oct 12, 2026 | T1 | 2,122,703 | 59,930 | 1,037,491 | 24,974 | 67.2% |
| Oct 5, 2026 | T1 | 1,718,029 | 48,143 | 627,106 | 18,843 | 73.3% |
| Sep 28, 2026 | T1 | 2,411,764 | 53,158 | 815,377 | 19,681 | 74.7% |
| Sep 21, 2026 | T1 | 1,561,694 | 44,519 | 810,929 | 20,731 | 65.8% |
| Sep 14, 2026 | T1 | 1,046,752 | 37,376 | 633,291 | 13,049 | 62.3% |
| Sep 7, 2026 | T1 | 1,091,821 | 31,642 | 384,375 | 13,943 | 74.0% |
| Aug 31, 2026 | T1 | 1,043,616 | 36,020 | 751,161 | 15,960 | 58.1% |
| Aug 24, 2026 | T1 | 753,288 | 32,544 | 449,970 | 15,737 | 62.6% |
| Aug 17, 2026 | T1 | 1,074,780 | 37,009 | 383,720 | 14,999 | 73.7% |
| Aug 10, 2026 | T1 | 1,177,987 | 42,249 | 383,153 | 16,072 | 75.5% |
| Aug 3, 2026 | T1 | 1,451,061 | 45,155 | 731,610 | 18,173 | 66.5% |