Earnings per Share

Basic and diluted earnings per share are calculated as follows:



	For the Years Ended December 31,
(In millions)	2018		2017		2016
Numerator:
Net income attributable to Biogen Inc.	$	4,430.7	$	2,539.1	$	3,702.8
Denominator:
Weighted average number of common shares outstanding	204.9		212.6		218.4
Effect of dilutive securities:
Stock options and employee stock purchase plan	—		0.1		0.1
Time-vested restricted stock units	0.3		0.2		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	—		—		—
Dilutive potential common shares	0.4		0.4		0.4
Shares used in calculating diluted earnings per share	205.3		213.0		218.8

Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.

Earnings per share for the years ended December 31, 2018, 2017 and 2016, reflects, on a weighted average basis, the repurchase of approximately 14.8 million shares, 3.7 million shares and 0.7 million shares of our common stock, respectively, under our 2018, 2016 and 2011 Share Repurchase Programs.

The adjustments related to the spin-off of our hemophilia business did not have a material impact on the potentially dilutive securities to be considered in the calculation of diluted earnings per share of common stock.