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, 2009			For the year ended December 31,
				2008		2007		2006			2005			2004
	(Dollars in millions)
Earnings:
Income before income taxes	$	(44	)	$	271	$	988	$	1,127		$	1,209		$	1,097
Less:
Interest on tax liabilities		(19	)		9		5		(a	)		(a	)		(a	)
Income before income taxes after interest on tax liabilities		(25	)		262		983		1,127			1,209			1,097
Plus:
Fixed charges		475			1,260		1,748		1,458			788			448
Earnings, including interest on deposits		450			1,522		2,731		2,585			1,997			1,545
Less:
Interest on deposits		320			734		1,167		1,005			548			315
Earnings, excluding interest on deposits	$	130		$	788	$	1,564	$	1,580		$	1,449		$	1,230
Fixed charges:
Interest expense	$	455		$	1,236	$	1,727	$	1,439		$	770		$	427
Interest portion of rental expense		20			24		21		19			18			21
Total fixed charges		475			1,260		1,748		1,458			788			448
Less:
Interest on deposits		320			734		1,167		1,005			548			315
Total fixed charges, excluding interest on deposits	$	155		$	526	$	581	$	453		$	240		$	133
Earnings to fixed charges:
Including interest on deposits		(b	)		1.50x		2.69x		3.49x			6.05x			9.30x
Excluding interest on deposits		(b	)		1.21x		1.56x		1.77x			2.54x			3.45x

(a) Prior to the fiscal year ending December 31, 2007, interest on tax liabilities was classified in income before income taxes.

(b) For the nine months ended September 30, 2009, earnings were insufficient to cover fixed charges, excluding or including interest on deposits, by $25,000,000.

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

	For the nine months ended September 30, 2009			For the year ended December 31,
				2008		2007		2006			2005			2004
	(Dollars in millions)
Earnings:
Income before income taxes	$	(44	)	$	271	$	988	$	1,127		$	1,209		$	1,097
Less:
Interest on tax liabilities		(19	)		9		5		(a	)		(a	)		(a	)
Income before income taxes after interest on tax liabilities		(25	)		262		983		1,127			1,209			1,097
Plus:
Fixed charges (excluding preferred stock dividends)		475			1,260		1,748		1,458			788			448
Earnings, including interest on deposits		450			1,522		2,731		2,585			1,997			1,545
Less:
Interest on deposits		320			734		1,167		1,005			548			315
Earnings, excluding interest on deposits	$	130		$	788	$	1,564	$	1,580		$	1,449		$	1,230
Fixed charges:
Interest expense	$	455		$	1,236	$	1,727	$	1,439		$	770		$	427
Interest portion of rental expense		20			24		21		19			18			21
Dividends on preferred stock		101			17		—		—			—			—
Total fixed charges		576			1,277		1,748		1,458			788			448
Less:
Interest on deposits		320			734		1,167		1,005			548			315
Total fixed charges, excluding interest on deposits	$	256		$	543	$	581	$	453		$	240		$	133
Earnings to fixed charges:
Including interest on deposits		(b	)		1.45x		2.69x		3.49x			6.05x			9.30x
Excluding interest on deposits		(b	)		1.19x		1.56x		1.77x			2.54x			3.45x

(a) Prior to the fiscal year ending December 31, 2007, interest on tax liabilities was classified in income before income taxes.

(b) For the nine months ended September 30, 2009, earnings were insufficient to cover combined fixed charges and preferred share dividends, excluding or including interest on deposits, by $126,000,000.