Basic (loss) earnings per share is computed by dividing (loss) income available to common shareholders by the weighted-average number of shares of common stock outstanding during the period. Diluted earnings per share is computed by dividing income available to common shareholders by the weighted-average number of shares of common stock outstanding during the period increased to include the number of additional shares of common stock that would have been outstanding if the potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, shares to be purchased under the Company’s ESPP and Canadian ESPP, RSUs, PSUs and, the impact of the Series A Preferred Stock prior to conversion on September 14, 2018. The effect of potentially dilutive securities is reflected in diluted earnings per share by application of the "treasury stock method" for outstanding stock-based compensation awards. Under the treasury stock method, an increase in the fair market value of the Company’s common stock can result in a greater dilutive effect from potentially dilutive securities. For the issue of Series A Preferred Stock, we used the "if-converted method", weighted for the period prior to conversion. Under the if-converted method, the preferred dividend applicable to Series A Preferred Stock was added back as an adjustment to the numerator. The Series A Preferred Stock shares were assumed to be converted to common shares at the beginning of the period or, if later, at the time of issuance, and through their conversion on September 14, 2018, for the year ended December 31, 2018, these common shares are weighted for the period the Series A Preferred Stock was outstanding with the resulting weighted average common shares included in the denominator. In applying the if-converted method, conversion is not assumed for purposes of computing diluted earnings per share if the effect would be anti-dilutive. The numerator was also adjusted for any premium or discount arising from redemption of the Series A Preferred Stock.

The following table sets forth the computation of basic and diluted (loss) earnings per share:

In millions, except per share data
	Years Ended December 31,
	2018			2017			2016
Numerator:
Net (loss) income attributable to Stericycle, Inc.	$	(244.7	)	$	42.4		$	206.3
Mandatory convertible preferred stock dividend		(25.5	)		(36.3	)		(39.4	)
Gain on repurchase of preferred stock		16.9			17.3			11.3
Numerator for basic (loss) earnings per share attributable to Stericycle, Inc. common shareholders	$	(253.3	)	$	23.4		$	178.2
Denominator:
Denominator for basic (loss) earnings per share - weighted average shares ⁽¹⁾		87.1			85.3			84.9
Effect of dilutive securities:
Stock-based compensation awards ⁽²⁾		-			0.3			0.7
Mandatory convertible preferred stock ⁽³⁾		-			-			-
Denominator for diluted (loss) earnings per share - adjusted weighted average shares and after assumed exercises		87.1			85.6			85.6
(Loss) earnings per share – Basic	$	(2.91	)	$	0.27		$	2.10
(Loss) earnings per share – Diluted	$	(2.91	)	$	0.27		$	2.08

In 2018, 2017, and 2016, options to purchase shares (in thousands) of 4,664, 4,724, and 3,411, respectively, at exercise prices of $47.52-$141.56, $62.50-$141.56, and $83.49-$141.56, respectively, were not included in the computation of diluted (loss) earnings per share because the effect would have been anti-dilutive.

In 2018, 2017, and 2016, RSUs (in thousands) of 169, 218, and 48, respectively, were not included in the computation of diluted (loss) earnings per share because the effect would have been anti-dilutive.

During 2018 and 2017, the Company had outstanding PSUs (in thousands) that were eligible to vest into a maximum of 116 and 11 shares of common stock, respectively, subject to the achievement of specified performance conditions. Contingently issuable shares are excluded from the computation of diluted earnings per share if, based on current period results, the shares would not be issuable if the end of the reporting period were the end of the contingency period or if the Company incurred a net loss attributable to its common shareholders. These outstanding PSUs have been excluded from the (loss) earnings per share calculation for 2018 and 2017 as the performance conditions were not satisfied as of the end of the respective periods.