Earnings per Share (Tables)

3 Months Ended

Mar. 31, 2022

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)	2022		2021
Numerator:
Net income attributable to Biogen Inc.	$	303.8	$	410.2
Denominator:
Weighted average number of common shares outstanding	147.1		151.9
Effect of dilutive securities:
Time-vested restricted stock units	0.3		0.2
Market stock units	0.1		0.1
Performance stock units settled in stock	0.1		0.1
Dilutive potential common shares	0.5		0.4
Shares used in calculating diluted earnings per share	147.6		152.3