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BIIB

Biogen Inc. Common Stock

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BIIB in the last 90 days

Biogen Inc. Common Stock (BIIB) had 2 congress transactions by 2 members and no insider purchases in filings from the last 90 days.

FINRA’s latest report (settlement 15 SEPT 2026) shows 5,817,797 shares held short, 7.6 days to cover, up 1.6% from the report before.

  • Congress: 0 purchases and 2 sales reported, amounts in the bands the law requires.
  • Delay: each filing below shows how many days passed between the trade and its publication. None of this is real-time.

Latest filing on file: 01 SEPT 2026 · FINRA settlement 15 SEPT 2026 · public filings, reported as filed

What the price is doing

$215$172 → $215 · +25% over six months

BIIB is up 25%. Short sellers still aren't backing off.

Bets against it — they pay off if the price falls — are up 30% over the same stretch.

$172 STARTAPRMAYJUNJULAUGSEPT11 MAY 2026 — Hon. Maria Elvira Salazar — $1,001 – $15,00011 MAY 2026 — Hon. Maria Elvira Salazar — $50,001 – $100,00012 MAY 2026 — Hon. Maria Elvira Salazar — $1,001 – $15,00005 JUN 2026 — Hon. Gilbert Cisneros — $1,001 – $15,00002 JUN 2026 — Hon. Maria Elvira Salazar — $15,001 – $50,00018 AUG 2026 — Hon. Kevin Hern — $1,001 – $15,000NOW $215

Politician activityBoughtSold

Short sellers

11 reports · twice a month

APR 0%peak +36%15 SEPT +30%APRMAYJUNJULAUGSEPT

Money betting BIIB falls. Reported twice a month, and it shows up seven working days late.

Politicians

4 buys · 2 sales

Traded over six months

View activity →

Short sellers

Bets up 30%

Over six months · newest 15 SEPT 2026

See the numbers →

Insiders

Nothing reported

Traded over six months

Quiet Money

Our take on how well BIIB holds up when sellers show up.

How it holds up · last 60 trading days

Through 10 SEPT 2026

Mixed

When BIIB gets hit lately, it goes both ways.

Lately, BIIB holds firm some days and gives way on others.

That's been true for the last 38 trading days.

The last 6 months

ResilientMixedVulnerable
APRMAYJUNJULAUG
20 MAR 2026Now · 10 SEPT 2026

What the filings show

What the filings show · last 90 days

2 of 4 sources

-28Tilted out

Leaning outBalancedLeaning in

The disclosed money is leaning away from this name, on what has actually been filed. This reads on two of the four sources we track.

Short interest
Short interest fell 3.0% — 5,999,133 to 5,817,797 shares between 15 JUL 2026 and 15 SEPT 2026. See the filings →
+8
Congress
2 members of Congress disclosed 0 purchases and 2 sales. See the filings →
-100

This summarises filings that have already been published — it is not a forecast, a rating of the company, or advice. Every figure above is listed in full further down this page, with the document it came from.

FINRA short interest

Settlement 15 SEPT 2026 · shares held short

5,817,797shares held short

Days to cover

7.59

Avg daily volume

766,507

Since last report

+1.59%

As of 15 September 2026, 5,817,797 Biogen Inc. Common Stock shares were held short — the total across every reporting firm, not one fund's position. That is 91,166 shares more than the previous report, a 1.59% increase. At the average daily volume of 766,507 shares, that position represents 7.59 days of trading — what the filing calls days to cover.

This is the most recent figure that exists, and it is 17 days old. FINRA collects short interest twice a month, on a settlement date, and publishes it about eight business days later. So nobody has a live short-interest number for BIIB — not us, and not anyone quoting one. We print the settlement date on the figure so you always know which day you are looking at.

Across the 12 reports we hold, the position has risen from 3,826,441 shares on 31 March 2026 to 5,817,797 today, a change of 52.0%. The highest reading in that window was 5,999,133 shares on 15 July 2026.

SettlementShares shortDays to cover
15 SEPT 20265,817,7977.59
31 AUG 20265,726,6318.66
14 AUG 20265,190,5556.13
31 JUL 20265,453,9014.73
15 JUL 20265,999,1333.45
30 JUN 20265,723,1944.14
15 JUN 20265,188,8365.65
29 MAY 20264,771,4954.49
15 MAY 20264,729,9584.21
30 APR 20264,475,4703.59
15 APR 20264,414,9583.07
31 MAR 20263,826,4413.47
What is BIIB's short interest?
5,817,797 shares, as of the 15 September 2026 settlement date. That is the figure FINRA published, unadjusted.
What percentage of the float is short?
We do not publish that, because FINRA does not publish float. The regulator reports the number of shares held short; turning it into a percentage needs a share count from somewhere else, and different sources disagree about what counts as float. We would rather give you the number that was actually filed than a percentage built on an assumption.
How current is this?
It is 17 days old, and that is as fresh as short interest gets. FINRA measures it twice a month and publishes it seven business days after the settlement date. Any site showing you a "live" short interest figure is showing you something else.
What does days to cover mean?
It is the short position divided by average daily trading volume — here, 7.59. It describes how many days of ordinary trading the position is equivalent to. It is arithmetic from the filing, not a prediction about what will happen.
Where does this come from?
FINRA's consolidated short interest file, which is public. We read it directly and store it unchanged, except that we blank the days-to-cover placeholder FINRA writes when a stock has almost no volume.

Disclosed insider buying on file

—no purchase on file passed the price check

Open-market purchases only — the amount is a fact, not a verdict.

On file here

Short positions0

Insider purchases0

Congress transactions10

Latest change01 SEPT 2026

SHORT POSITIONS · 0INSIDER BUYS · 0CONGRESS · 10

Congress transactions on file

10 disclosed · newest first · every row links to its filing

WhoAmount as filedTradedFiledLag
Hon. Kevin HernSOLD$1,001 – $15,00018 AUG 202601 SEPT 202614 days
Hon. Maria Elvira SalazarSOLD$15,001 – $50,00002 JUN 202607 JUL 202635 days
Hon. Gilbert CisnerosBOUGHT$1,001 – $15,00005 JUN 202602 JUL 202627 days
Hon. Maria Elvira SalazarBOUGHT$1,001 – $15,00012 MAY 202608 JUN 202627 days
Hon. Maria Elvira SalazarBOUGHT$50,001 – $100,00011 MAY 202608 JUN 202628 days
Hon. Maria Elvira SalazarBOUGHT$1,001 – $15,00011 MAY 202608 JUN 202628 days
Hon. Gilbert CisnerosBOUGHT$1,001 – $15,00030 JAN 202613 FEB 202614 days
Hon. Rob BresnahanBOUGHT$1,001 – $15,00015 MAY 202509 JUN 202525 days
Hon. Rob BresnahanSOLD$1,001 – $15,00008 APR 202508 MAY 202530 days
Hon. Rob BresnahanBOUGHT$1,001 – $15,00025 FEB 202527 MAR 202530 days
What this page will never showNo price targetsNo score out of 100No buy or sell callsNo predictionsDocuments, dates, and how late they were.