12. Earnings per Share

Total outstanding shares as of March 31, 2019 and 2018 were 102.5 million and 107.8 million, respectively. Under our stock repurchase program, for the three months ended March 31, 2019 and 2018, we repurchased and retired 1.3 million and 0.8 million shares, respectively. For the three months ended March 31, 2019 and 2018, we acquired 0.5 million and 0.6 million shares, respectively, related to tax withholding for share-based compensation.

The calculation of basic earnings per share of common stock is based on the weighted average number of shares of common stock outstanding in the year, or period, over which they were outstanding. Our calculation of diluted earnings per share of common stock assumes that any shares of common stock outstanding were increased by shares that would be issued upon exercise of those stock awards for which the average market price for the period exceeds the exercise price less the shares that could have been purchased by the Company with the related proceeds, including compensation expense measured but not yet recognized.

Our weighted-average shares outstanding for the three months ended March 31, 2019 and 2018 was as follows:



	Three Months Ended March 31,
(in millions)	2019	2018
Weighted-average number of shares of common stock outstanding - basic	102.3	106.8
Stock options	—	1.2
Restricted stock units	—	2.0
Weighted-average shares and assumed conversions - diluted⁽¹⁾	102.3	110.0

(1)

Due to the net loss during the three months ended March 31, 2019, the denominator in the diluted earnings per share calculation does not include the effects of the stock awards for which the average market price for the period exceeds the exercise price, as it would result in a less dilutive computation. As a result, reported diluted earnings per share for the three months ended March 31, 2019 are the same as basic earnings per share.

Awards of potentially dilutive shares of common stock, which have exercise prices that were higher than the average market price during the period, are not included in the computation of dilutive earnings per share as their effect would have been anti-dilutive. For the three months ended March 31, 2019 and 2018 the number of anti-dilutive shares was approximately 5.8 million and 2.8 million, respectively.