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Earnings per Share (Tables) | 3 Months Ended
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Mar. 31, 2025
Earnings Per Share [Abstract] |
Basic and diluted earnings per share | Basic and diluted shares outstanding used in our earnings per share calculation are calculated as follows:
|  | For the Three Months Ended March 31, |  |
(In millions) |  | 2025 |  | 2024 |  |  |  |
Numerator: |  |  |  |  |  |  |  |
Net income attributable to Biogen Inc. |  | $ | 240.5 |  |  | $ | 393.4 |  |  |  |  |
Denominator: |  |  |  |  |  |  |  |
Weighted average number of common shares outstanding |  | 146.1 |  |  | 145.2 |  |  |  |  |
Effect of dilutive securities: |  |  |  |  |  |  |  |
Time-vested restricted stock units |  | 0.5 |  |  | 0.5 |  |  |  |  |
Performance stock units settled in stock |  | — |  |  | 0.2 |  |  |  |  |
Dilutive potential common shares |  | 0.5 |  |  | 0.7 |  |  |  |  |
Shares used in calculating diluted earnings per share |  | 146.6 |  |  | 145.9 |  |  |  |  |

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 260 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482662/260-10-50-1 + Details
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