<PAGE>


                                                                 EXHIBIT (12)(b)

                            CONSUMERS ENERGY COMPANY
      Ratio of Earnings to Combined Fixed Charges and Preferred Dividends
                               and Distributions
                              (Millions of Dollars)

<Table>
<Caption>
                                                     Years Ended December 31

                                             2005     2004     2003     2002     2001
                                            -----    -----    -----    -----    -----
                                             (b)
<S>                                         <C>      <C>      <C>      <C>      <C>
Earnings as defined (a)
Pretax income from continuing operations     (590)   $ 439    $ 333    $ 543    $ 296
Exclude equity basis subsidiaries (c)          (1)      (1)     (42)     (53)     (38)
Include equity basis dividends
received (c)                                            --       45       15        8
Fixed charges as defined, adjusted to
exclude capitalized interest of $38,
$(25), $9, $12, and $6 for the years
ended December 31, 2005, 2004, 2003,
2002, and 2001, respectively (d)              281      373      255      225      241
                                            -----    -----    -----    -----    -----
Earnings as defined                         $(310)   $ 811    $ 591    $ 730    $ 507
                                            =====    =====    =====    =====    =====

Fixed charges as defined (a)
Interest on long-term debt (e)              $ 304    $ 328    $ 241    $ 153    $ 151
Estimated interest portion of lease
rental                                          6        4        7       10       11
Other interest charges                          6       13       13       27       41
Preferred dividends and
distributions (e)                               3        3        3       47       44
                                            -----    -----    -----    -----    -----
Fixed charges as defined                    $ 319    $ 348    $ 264    $ 237    $ 247
                                            =====    =====    =====    =====    =====
Ratio of earnings to combined fixed
charges and preferred dividends and
distributions                                  --     2.33     2.24     3.08     2.05
                                            =====    =====    =====    =====    =====
</Table>

NOTES:

(a) Earnings and fixed charges as defined in instructions for Item 503 of
Regulation S-K.

(b) For the year ended December 31, 2005, fixed charges exceeded earnings by
$629 million. Earnings as defined include asset impairment charges of $1.184
billion.

(c) In 2004, we consolidated the MCV Partnership and the FMLP in accordance with
Revised FASB Interpretation No. 46.

(d) For 2004, fixed charges, adjusted as defined, include $25 million of
interest cost that was capitalized prior to 2004 and subsequently expensed in
2004.

(e) We determined that we do not hold the controlling interest in our trust
preferred security structures and those securities were deconsolidated as of
December 31, 2003. Therefore, our trust preferred securities that were
previously included in mezzanine equity are reflected in long-term debt.