<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, 1999 and 1998 and for the five years ended December 31,
1998 were as follows:

<TABLE>
<CAPTION>
                                     Three Months Ended           
                                          March 31,                   Years Ended December 31,    
                                          ---------       ---------------------------------------------
(Dollars in millions)
                                        1999     1998     1998      1997      1996      1995      1994
                                        ----     ----     -----     -----     -----     -----     -----
<S>                                  <C>      <C>      <C>       <C>       <C>       <C>       <C> 
Net income                            $  223   $  238   $   792   $   879   $   650   $   678   $   542
Extraordinary item, net of tax                                                                        7
Income tax expense                       131      153       477       589       483       529       422
                                      ------   ------   -------   -------   -------   -------   ------- 
     Pretax earnings                  $  354   $  391   $ 1,269   $ 1,468   $ 1,133   $ 1,207   $   971
                                      ======   ======   =======   =======   =======   =======   ======= 
Fixed charges:
  Portion of rental expense            
    (net of sublease                   
     rental income) which              
     approximates the                  
     interest factor                  $   12   $   10   $    42   $    39   $    40   $    38   $    35
  Interest on borrowed funds             264      272     1,179     1,050       873     1,079     1,038
                                      ------   ------   -------   -------   -------   -------   ------- 
     Total fixed charges                 276      282     1,221     1,089       913     1,117     1,073
                                       
Preferred stock dividend               
  requirements                             0        7        15        53        65        68        67
                                      ------   ------   -------   -------   -------   -------   ------- 
Total combined fixed charges           
  and preferred stock dividend         
  requirements                        $  276   $  289   $ 1,236   $ 1,142   $   978   $ 1,185   $ 1,140
                                      ======   ======   =======   =======   =======   =======   ======= 
                                       
Earnings (for ratio calculation)       
  (Pretax earnings                     
  plus total fixed charges)           $  630   $  673   $ 2,490   $ 2,557   $ 2,046   $ 2,324   $ 2,044
                                      ======   ======   =======   =======   =======   =======   ======= 
                                       
Ratio of earnings to combined          
  fixed charges and preferred          
  stock dividend requirements           2.28     2.33      2.01      2.24      2.09      1.96      1.79
                                      ======   ======   =======   =======   =======   =======   ======= 
</TABLE>
For purposes of computing the consolidated ratio of earnings to combined fixed
charges and preferred stock dividend requirements "earnings" represent income
before extraordinary item 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.