Interstate Power & Light (IPLDP) 10-Q 2012 Q1 Quarterly report

Exhibit 12.1

ALLIANT ENERGY CORPORATION

RATIO OF EARNINGS TO FIXED CHARGES

	Three Months Ended March 31,						Years Ended Dec. 31,
	2012			2011			2011			2010			2009			2008			2007
	(dollars in millions)
EARNINGS:
Net income from continuing operations attributable to Alliant Energy Corporation common shareowners	$	39.3		$	72.0		$	323.1		$	291.5		$	111.6		$	265.8		$	415.7
Income tax expense (benefit) (a)		27.7			22.4			69.0			147.6			(6.8	)		130.6			249.9
Subtotal		67.0			94.4			392.1			439.1			104.8			396.4			665.6
Fixed charges as defined		50.2			51.6			208.4			215.4			199.7			185.2			184.6
Adjustment for undistributed equity earnings		(0.8	)		(1.6	)		(7.0	)		(5.9	)		(6.7	)		(6.1	)		(7.8	)
Less:
Interest capitalized		1.6			—			2.7			—			—			—			—
Preferred dividend requirements of subsidiaries (pre-tax basis) (b)		6.6			8.0			22.0			27.6			17.7			27.3			29.5
Total earnings as defined	$	108.2		$	136.4		$	568.8		$	621.0		$	280.1		$	548.2		$	812.9
FIXED CHARGES:
Interest expense	$	38.9		$	40.5		$	158.3		$	162.8		$	154.8		$	125.8		$	116.7
Interest capitalized		1.6			—			2.7			—			—			—			—
Estimated interest component of rent expense		3.1			3.1			25.4			25.0			27.2			32.1			38.4
Preferred dividend requirements of subsidiaries (pre-tax basis) (b)		6.6			8.0			22.0			27.6			17.7			27.3			29.5
Total fixed charges as defined	$	50.2		$	51.6		$	208.4		$	215.4		$	199.7		$	185.2		$	184.6
Ratio of Earnings to Fixed Charges (c)		2.16			2.64			2.73			2.88			1.40			2.96			4.40

(a) Includes net interest related to unrecognized tax benefits.

(b) Preferred dividend requirements of subsidiaries (pre-tax basis) are computed by dividing the preferred dividend requirements of subsidiaries by one hundred percent minus the respective year-to-date effective income tax rate.

(c) The ratio calculation in the above table relates to Alliant Energy Corporation's continuing operations.