Biogen Inc. (BIIB)

Highly Crowded

Held by 960 of 5,944 reporting institutions (99th percentile) — extremely crowded.

Data as of Q1 2026

Institutional Ownership

90.34%

QoQ Change

-6.24%

Total Value

$23.7T

Shares Outstanding

147.6M

Crowding AnalysisHighly Crowded

Holders960of 5,944

Avg: 68

Uncrowded99th percentileCrowded

Institutional Activity

Buy/Sell Ratio1.23x

97th percentile

529 buying431 selling

+132

New

-133

Closed

-8,100,506

Net shares

Holding Period Distribution

estimate

Median: 4 QAvg: 4 QHolders: 960

Ownership Concentration

Top 5: 45.2%Top 10: 58.7%

BlackRock,12.0%

PRIMECAP MANAGEMENT CO/CA/11.1%

FMR9.6%

VANGUARD CAPITAL MANAGEMENT7.2%

STATE STREET5.4%

Others (955)54.8%

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Conviction-Weighted Ownership

Median weight: 0.05%Avg weight: 0.27%Max: 2.13%High conviction (>1%): 1

BlackRock,

PRIMECAP MANAGEMENT CO/CA/

FMR

VANGUARD CAPITAL MANAGEMENT

STATE STREET

VANGUARD PORTFOLIO MANAGEMENT

GEODE CAPITAL MANAGEMENT,

WELLINGTON MANAGEMENT GROUP LLP

MORGAN STANLEY

JPMORGAN CHASE &

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Whale Moves Timeline (8 Quarters)

Biggest dollar-value position changes among top 10 holders

NEWVANGUARD CAPITAL MANAGEMENT$1.7B9.5M shr

NEWVANGUARD PORTFOLIO MANAGEMENT$1.2B6.5M shr

BOUGHTFMR$620M3.4M shr

NEWJPMORGAN CHASE$378M2.0M shr

BOUGHTBlackRock$213M1.2M shr

NEWFMR$1.7B9.4M shr

NEWNORGES BANK$464M2.6M shr

SOLDPoint72 Asset Management, L.P.$186M1.1M shr

SOLDWELLINGTON MANAGEMENT GROUP LLP$122M695K shr

SOLDPRIMECAP MANAGEMENT CO/CA$35M197K shr

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Institutional Trends (8 Quarters)

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Institutional Holders

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