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				Six Months Ended
	October 31,				October 31,
(Dollars in millions, except per share amounts)	2016		2017		2016		2017
Net income available to common stockholders	$	197	$	239	$	342	$	417
Share data (in thousands):
Basic average common shares outstanding	389,050		384,120		390,994		384,076
Dilutive effect of stock-based awards	2,798		2,507		2,895		2,428
Diluted average common shares outstanding	391,848		386,627		393,889		386,504

Basic earnings per share	$	0.51	$	0.62	$	0.87	$	1.08
Diluted earnings per share	$	0.50	$	0.62	$	0.87	$	1.08

We excluded common stock-based awards for approximately 1,937,000 shares and 1,201,000 shares from the calculation of diluted earnings per share for the three months ended October 31, 2016 and 2017, respectively. We excluded common stock-based awards for approximately 1,555,000 shares and 1,288,000 shares from the calculation of diluted earnings per share for the six months ended October 31, 2016 and 2017, respectively. We excluded those awards because they were not dilutive for those periods under the treasury stock method.