10. Basic and diluted earnings (loss) per share

Basic earnings (loss) per share are calculated by dividing net income (loss) by the weighted average common shares outstanding during their respective period. Diluted earnings (loss) per share are 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, 2013. 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. The following table sets forth the diluted net income and potentially dilutive shares utilized in the per share calculation for the three and six months ended June 30, 2013 and 2012:

	Three months ended June 30,						Six months ended June 30,

	2013			2012			2013		2012
Numerator:
Income (loss) from continuing operations attributable to Atlantic Power Corporation	$	(2.3	)	$	(24.4	)	$	3.3	$	(78.3	)
Income (loss) from discontinued operations, net of tax		(0.7	)		19.3			0.2		30.9

Net income (loss) attributable to Atlantic Power Corporation	$	(3.0	)	$	(5.1	)	$	3.5	$	(47.4	)
Denominator:
Weighted average basic shares outstanding		119.9			113.7			119.7		113.6
Dilutive potential shares:
Convertible debentures		27.7			13.3			27.7		13.3
LTIP notional units		0.8			0.5			0.6		0.5

Potentially dilutive shares		148.4			127.5			148.0		127.4

Diluted earnings (loss) per share from continuing operations attributable to Atlantic Power Corporation	$	(0.02	)	$	(0.21	)	$	0.03	$	(0.69	)
Diluted earnings (loss) per share from discontinued operations		(0.01	)		0.17			0.00		0.27

Diluted earnings (loss) per share attributable to Atlantic Power Corporation	$	(0.03	)	$	(0.04	)	$	0.03	$	(0.42	)

Potentially dilutive shares from convertible debentures and LTIP notional units have been excluded from fully diluted shares for the three months ended June 30, 2013 and the three and six months ended June 30, 2012 because their impact would be anti-dilutive. Potentially dilutive shares from convertible debentures have been excluded from fully diluted shares for the six months ended June 30, 2013 because their impact would be anti-dilutive.