10. Basic and diluted loss per share

Basic loss per share is calculated by dividing net loss by the weighted average common shares outstanding during their respective periods. Diluted loss per share is computed including dilutive potential shares as if they were outstanding shares during the year. Dilutive potential shares include the weighted average number of shares, as of the date such notional units were granted, that would be issued if the unvested notional units outstanding under the LTIP were vested and redeemed for shares under the terms of the LTIP.

Because we reported a loss for the three and nine months ended September 30, 2017 and 2016, respectively, diluted earnings per share are equal to basic earnings per share as the inclusion of potentially dilutive shares in the computation is anti-dilutive.

The following table sets forth the diluted net income and potentially dilutive shares utilized in the per share calculation for the three and nine months ended September 30, 2017 and 2016:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Numerator:
Net loss attributable to Atlantic Power Corporation	$	(32.9)	$	(82.4)	$	(57.5)	$	(116.2)
Denominator:
Weighted average basic shares outstanding		115.3		119.3		115.1		120.9
Dilutive potential shares:
Convertible debentures		8.1		8.1		8.1		14.9
LTIP notional units		—		0.1		—		0.1
Potentially dilutive shares		123.4		127.5		123.2		135.9
Basic and diluted loss per share attributable to Atlantic Power Corporation	$	(0.29)	$	(0.69)	$	(0.50)	$	(0.96)

The dilutive effect of our convertible debentures is calculated using the “if-converted method.” Under the if-converted method, the debentures are assumed to be converted at the beginning of the period, and the resulting common shares are included in the denominator of the diluted EPS calculation for the entire period being presented. Interest expense, net of any income tax effects, would be added back to the numerator for purposes of the if-converted calculation. Potentially dilutive shares from convertible debentures of $8.1 million and $8.1 million have been excluded from fully diluted shares in the three and nine months ended September 30, 2017, respectively, because their impact would be anti-dilutive. Potentially dilutive shares from convertible debentures of $8.1 million and $14.9 million have been excluded from fully diluted shares in the three and nine months ended September 30, 2016, respectively, because their impact would be anti-dilutive.