Earnings Per Share

We calculate basic earnings per share by dividing net income available to common stockholders by the weighted average number of common shares outstanding during the period. Diluted earnings per share further includes the dilutive effect of stock-based compensation awards. We calculate that dilutive effect using the “treasury stock method” (as defined by GAAP).

The following table presents information concerning basic and diluted earnings per share:



	Three Months Ended				Nine Months Ended
	January 31,				January 31,
(Dollars in millions, except per share amounts)	2018		2019		2018		2019
Net income available to common stockholders	$	190	$	227	$	607	$	676

Share data (in thousands):
Basic average common shares outstanding	480,361		477,301		480,193		479,522
Dilutive effect of stock-based awards	3,883		2,798		3,318		3,143
Diluted average common shares outstanding	484,244		480,099		483,511		482,665

Basic earnings per share	$	0.39	$	0.47	$	1.26	$	1.41
Diluted earnings per share	$	0.39	$	0.47	$	1.25	$	1.40

We excluded common stock-based awards for approximately 0 shares and 548,000 shares from the calculation of diluted earnings per share for the three months ended January 31, 2018 and 2019, respectively. We excluded common stock-based awards for approximately 1,073,000 shares and 414,000 shares from the calculation of diluted earnings per share for the nine months ended January 31, 2018 and 2019, respectively. We excluded those awards because they were not dilutive for those periods under the treasury stock method.