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Earnings per Share | 3 Months Ended
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Mar. 31, 2024
Earnings Per Share [Abstract] |
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) |  | 2024 |  | 2023 |  |  |  |
Numerator: |  |  |  |  |  |  |  |
Net income attributable to Biogen Inc. |  | $ | 393.4 |  |  | $ | 387.9 |  |  |  |  |
Denominator: |  |  |  |  |  |  |  |
Weighted average number of common shares outstanding |  | 145.2 |  |  | 144.4 |  |  |  |  |
Effect of dilutive securities: |  |  |  |  |  |  |  |
Time-vested restricted stock units |  | 0.5 |  |  | 0.6 |  |  |  |  |
Market stock units |  | — |  |  | 0.1 |  |  |  |  |
Performance stock units settled in stock |  | 0.2 |  |  | 0.1 |  |  |  |  |
Dilutive potential common shares |  | 0.7 |  |  | 0.8 |  |  |  |  |
Shares used in calculating diluted earnings per share |  | 145.9 |  |  | 145.2 |  |  |  |  |
Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.

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