Comerica (CMA) S-3ASR Automatic shelf registration

Exhibit 12.1

Computation of Ratios of Earnings To Fixed Charges

	For the nine months ended September 30, 2012			For the year ended December 31,
				2011			2010		2009			2008		2007
	(Dollars in millions)
Earnings:
Income before income taxes	$	525		$	530		$	315	$	(115	)	$	271	$	988
Less:
Interest and penalties on tax liabilities		(7	)		(6	)		5		(19	)		9		5
Income before income taxes after interest and penalties on tax liabilities		532			536			310		(96	)		262		983
Plus:
Fixed charges		121			181			231		564			1,259		1,747
Earnings, including interest on deposits		653			717			541		468			1,521		2,730
Less:
Interest on deposits		54			90			115		372			734		1,167
Earnings, excluding interest on deposits	$	599		$	627		$	426	$	96		$	787	$	1,563
Fixed charges:
Interest expense	$	103		$	156		$	207	$	538		$	1,236	$	1,727
Interest portion of rental expense		18			25			24		26			23		20
Total fixed charges		121			181			231		564			1,259		1,747
Less:
Interest on deposits		54			90			115		372			734		1,167
Total fixed charges, excluding interest on deposits	$	67		$	91		$	116	$	192		$	525	$	580
Earnings to fixed charges:
Excluding interest on deposits		8.90x			6.88x			3.67x		(a	)		1.50x		2.70x
Including interest on deposits		5.38x			3.97x			2.34x		(a	)		1.21x		1.56x

(a) For the year ended December 31, 2009, earnings were insufficient to cover combined fixed charges, excluding or including interest on deposits, by $96 million.

Computation of Ratios of Earnings To Combined Fixed Charges and Preferred Dividends

	For the nine months ended September 30, 2012			For the year ended December 31,
				2011			2010		2009			2008		2007
	(Dollars in millions)
Earnings:
Income before income taxes	$	525		$	530		$	315	$	(115	)	$	271	$	988
Less:
Interest and penalties on tax liabilities		(7	)		(6	)		5		(19	)		9		5
Income before income taxes after interest and penalties on tax liabilities		532			536			310		(96	)		262		983
Plus:
Fixed charges (excluding preferred stock dividends)		121			181			231		564			1,259		1,747
Earnings, including interest on deposits		653			717			541		468			1,521		2,730
Less:
Interest on deposits		54			90			115		372			734		1,167
Earnings, excluding interest on deposits	$	599		$	627		$	426	$	96		$	787	$	1,563
Fixed charges:
Interest expense	$	103		$	156		$	207	$	538		$	1,236	$	1,727
Interest portion of rental expense		18			25			24		26			23		20
Dividends on preferred stock		—			—			150		134			21		—
Total fixed charges		121			181			381		698			1,280		1,747
Less:
Interest on deposits		54			90			115		372			734		1,167
Total fixed charges, excluding interest on deposits	$	67		$	91		$	266	$	326		$	546	$	580
Earnings to fixed charges:
Excluding interest on deposits		8.90x			6.88x			1.60x		(a	)		1.44x		2.70x
Including interest on deposits		5.38x			3.97x			1.42x		(a	)		1.19x		1.56x

(a) For the year ended December 31, 2009, earnings were insufficient to cover combined fixed charges and preferred share dividends, excluding or including interest on deposits, by $230 million.