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Earnings per Share | 6 Months Ended
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Jun. 30, 2021
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 June 30, |  | For the Six Months Ended June 30,
(In millions) |  | 2021 |  | 2020 |  | 2021 |  | 2020
Numerator: |  |  |  |  |  |  |  |
Net income attributable to Biogen Inc. |  | $ | 448.5 |  |  | $ | 1,542.1 |  |  | $ | 858.7 |  |  | $ | 2,941.2 |
Denominator: |  |  |  |  |  |  |  |
Weighted average number of common shares outstanding |  | 149.7 |  |  | 160.6 |  |  | 150.8 |  |  | 166.7 |
Effect of dilutive securities: |  |  |  |  |  |  |  |
Time-vested restricted stock units |  | 0.2 |  |  | 0.1 |  |  | 0.2 |  |  | 0.1 |
Market stock units |  | 0.1 |  |  | 0.1 |  |  | 0.1 |  |  | 0.1 |
Performance stock units settled in stock |  | 0.1 |  |  | 0.1 |  |  | 0.1 |  |  | 0.1 |
Dilutive potential common shares |  | 0.4 |  |  | 0.3 |  |  | 0.4 |  |  | 0.3 |
Shares used in calculating diluted earnings per share |  | 150.1 |  |  | 160.9 |  |  | 151.2 |  |  | 167.0 |
Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.

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