Earnings per Share (Tables)

6 Months Ended

Jun. 30, 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 June 30,				For the Six Months Ended June 30,
(In millions)	2022		2021		2022		2021
Numerator:
Net income attributable to Biogen Inc.	$	1,058.0	$	448.5	$	1,361.8	$	858.7
Denominator:
Weighted average number of common shares outstanding	145.9		149.7		146.5		150.8
Effect of dilutive securities:
Time-vested restricted stock units	0.2		0.2		0.2		0.2
Market stock units	—		0.1		—		0.1
Performance stock units settled in stock	0.1		0.1		0.1		0.1
Dilutive potential common shares	0.3		0.4		0.3		0.4
Shares used in calculating diluted earnings per share	146.2		150.1		146.8		151.2