<PAGE>
 
                                                                   EXHIBIT 12(c)
                            BANKBOSTON CORPORATION
  COMPUTATION OF CONSOLIDATED RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND
                     PREFERRED STOCK DIVIDEND REQUIREMENTS

                       (Excluding Interest on Deposits)

The Corporation's ratios of earnings to combined fixed charges and preferred
stock dividend requirements (excluding interest on deposits) for the three
months ended March 31, 1998 and 1997 and for the five years ended December 31,
1997 were as follows:

<TABLE> 
<CAPTION> 
                                               Three Months Ended
                                                   March 31,                             Years Ended December 31,
                                             ----------------------    ------------------------------------------------------------
(Dollars in millions)                        
                                                  1998         1997         1997         1996         1995        1994         1993
                                             ---------    ---------    ---------    ---------    ---------   ---------    --------- 
<S>                                          <C>          <C>          <C>          <C>          <C>         <C>          <C> 
Net income                                   $     238    $     207    $     879    $     650    $     678   $     542    $     367
Extraordinary items, net of tax                                                                                      7
Cumulative effect of changes                 
   in accounting principles, net of tax                                                                                         (24)
Income tax expense                                 153          139          589          483          529         422          262
                                             ---------    ---------    ---------    ---------    ---------   ---------    --------- 
     Pretax earnings                         $     391    $     346    $   1,468    $   1,133    $   1,207   $     971    $     605
                                             =========    =========    =========    =========    =========   =========    ========= 
Fixed charges:                               
  Portion of rental expense                  
     (net of sublease                         
     rental income) which                    
     approximates the                        
     interest factor                         $      10    $      10    $      39    $      40    $      38   $      35    $      36
  Interest on borrowed funds                       272          255        1,050          873        1,079       1,038          384
                                             ---------    ---------    ---------    ---------    ---------   ---------    --------- 
     Total fixed charges                           282          265        1,089          913        1,117       1,073          420
                                             
Preferred stock dividend                     
  requirements                                       7           16           53           65           68          67           61
                                             ---------    ---------    ---------    ---------    ---------   ---------    --------- 
Total combined fixed charges                 
  and preferred stock dividend               
  requirements                               $     289    $     281    $   1,142    $     978    $   1,185   $   1,140    $     481
                                             =========    =========    =========    =========    =========   =========    ========= 
Earnings (for ratio calculation)             
  (Pretax earnings                           
  plus total fixed charges)                  $     673    $     611    $   2,557    $   2,046    $   2,324   $   2,044    $   1,025
                                             =========    =========    =========    =========    =========   =========    ========= 
Ratio of earnings to combined                
  fixed charges and preferred                
  stock dividend requirements                     2.33         2.17         2.24         2.09         1.96        1.79         2.13
                                             =========    =========    =========    =========    =========   =========    ========= 
</TABLE> 

For purposes of computing the consolidated ratio of earnings to combined fixed
charges and preferred stock dividend requirements "earnings" represent income
before extraordinary items and cumulative effect of changes in accounting
principles plus applicable income taxes and fixed charges. "Fixed charges"
include gross interest expense (excluding interest on deposits) and the
proportion deemed representative of the interest factor of rent expense, net of
income from subleases. Pretax earnings required for preferred stock dividends
were computed using tax rates for the applicable year.