18. Basic and diluted earnings (loss) per share

Basic earnings (loss) per share is calculated by dividing net income (loss) by the weighted average common shares outstanding during their respective period. Diluted earnings (loss) per share is computed including dilutive potential shares as if they were outstanding shares during the year. Dilutive potential shares include shares that would be issued if all of the convertible debentures were converted into shares at January 1, 2012. Dilutive potential shares also 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 years ended December 31, 2012, 2011 and 2010, 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 years ended December 31, 2012, 2011 and 2010:

	2012			2011			2010

Numerator:
Loss from continuing operations attributable to Atlantic Power Corporation	$	(129,235	)	$	(74,585	)	$	(27,879	)
Income from discontinued operations, net of tax		16,459			36,177			24,127

Net loss attributable to Atlantic Power Corporation	$	(112,776	)	$	(38,408	)	$	(3,752	)
Denominator:
Weighted average basic shares outstanding		116,426			77,466			61,706
Dilutive potential shares:
Convertible debentures		17,353			13,962			12,339
LTIP notional units		489			438			542

Potentially dilutive shares		134,268			91,866			74,587

Diluted loss per share from continuing operations attributable to Atlantic Power Corporation	$	(1.11	)	$	(0.96	)	$	(0.45	)
Diluted earnings per share from discontinued operations		0.14			0.46			0.39

Diluted loss per share attributable to Atlantic Power Corporation	$	(0.97	)	$	(0.50	)	$	(0.06	)

Potentially dilutive shares from convertible debentures and potentially dilutive shares from LTIP notional units have been excluded from fully diluted shares in the years ended December 31, 2012, 2011 and 2010 because their impact would be anti-dilutive.