Net Income per Common Share

Basic net income per common share is computed by dividing Net income attributable to SP Plus Corporation by the weighted average number of shares of common stock outstanding during the period. Diluted net income per common share is based upon the weighted average number of shares of common stock outstanding at period end, consisting of incremental shares assumed to be issued upon exercise of stock options and the incremental shares assumed to be issued under performance share and restricted stock unit arrangements, using the treasury-stock method.

A reconciliation of the basic weighted average common shares outstanding to diluted weighted average common shares outstanding is as follows:



	Year Ended December 31,
(millions, except share and per share data)	2017		2016		2015
Net income attributable to SP Plus Corporation	$	41.2	$	23.1	$	17.4
Basic weighted average common shares outstanding	22,195,350		22,238,021		22,189,140
Dilutive impact of share-based awards	312,938		290,101		322,619
Diluted weighted average common shares outstanding	22,508,288		22,528,122		22,511,759
Net income per common share
Basic	$	1.86	$	1.04	$	0.78
Diluted	$	1.83	$	1.03	$	0.77

As of December 31, 2017, the weighted average number of performance-based shares units related to the 2015 awards were included for the purposes of determining diluted net income per share as all performance goals were achieved as of this date. The 2016 and 2017 performance-based awards have been excluded for purposes of determining diluted net income per share for the year ended December 31, 2017, as all performance goals were not achieved relating to these awards as of December 31, 2017.

There are no additional securities that could dilute basic earnings per share in the future that were not included in the computation of diluted earnings per share, other than those disclosed.