Net Income Per Share

The Company's basic net income per share amounts have been computed by dividing net income by the weighted average number of shares of Common Stock and Class A Stock outstanding. Net income per share is presented on a combined basis, inclusive of Common Stock and Class A Stock outstanding, as each class of stock has equivalent economic rights. Diluted net income per share includes the potential dilutive effect of other securities as if such securities were converted or exercised during the period, when the effect is dilutive. The calculations of basic and diluted net income per share are as follows:



	Year Ended December 31,
	2018		2017		2016
Net income - basic	$	2,444.4	$	1,198.5	$	895.5
Effect of dilutive securities:
Convertible senior notes - interest expense and amortization of discount and note issuance costs	—		—		0.4
Net income - diluted	$	2,444.4	$	1,198.5	$	895.9

(Shares in millions)
Weighted average shares - basic	107.9		106.3		104.7
Effect of dilutive securities:
Stock options	6.9		9.1		10.2
Restricted stock	—		0.5		0.5
Warrants	—		—		0.9
Dilutive potential shares	6.9		9.6		11.6
Weighted average shares - diluted	114.8		115.9		116.3

Net income per share - basic	$	22.65	$	11.27	$	8.55
Net income per share - diluted	$	21.29	$	10.34	$	7.70

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive, include the following:



	Year Ended December 31,
(Shares in millions)	2018	2017	2016
Stock options	14.9	9.2	8.0