<PAGE>
 
                                                                   EXHIBIT 12(b)
                             BANKBOSTON CORPORATION
         COMPUTATION OF CONSOLIDATED RATIO OF EARNINGS TO FIXED CHARGES

                        (Including Interest on Deposits)

The Corporation's ratios of earnings to fixed charges (including interest on
deposits) for the nine months ended September 30, 1998 and 1997 and for the five
years ended December 31, 1997 were as follows:
<TABLE> 
<CAPTION> 
                                          Nine Months Ended
                                             September 30,                 Years Ended December 31,
                                          ------------------  ------------------------------------------------- 
(Dollars in millions)
                                            1998      1997      1997      1996      1995      1994      1993
                                          --------  --------  --------  --------  --------  --------  ---------
<S>                                       <C>       <C>       <C>       <C>       <C>       <C>       <C> 
Net income                                $    585  $    645  $    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                             360       434       589       483       529       422       262
                                          --------  --------  --------  --------  --------  --------  ---------
     Pretax earnings                      $    945  $  1,079  $  1,468  $  1,133  $  1,207  $    971  $    605
                                          ========  ========  ========  ========  ========  ========  =========
 
Fixed charges:
     Portion of rental expense
     (net of sublease
     rental income) which
     approximates the
     interest factor                      $     31  $     29  $     39  $     40  $     38  $     35  $     36
 
Interest on borrowed funds                     884       783     1,050       873     1,079     1,038       384
 
Interest  on deposits                        1,385     1,233     1,685     1,680     1,791     1,301     1,177
                                          --------  --------  --------  --------  --------  --------  ---------
          Total fixed charges             $  2,300  $  2,045  $  2,774  $  2,593  $  2,908  $  2,374  $  1,597
                                          ========  ========  ========  ========  ========  ========  =========
 
Earnings (for ratio calculation)          $  3,245  $  3,124  $  4,242  $  3,726  $  4,115  $  3,345  $  2,202
                                          ========  ========  ========  ========  ========  ========  =========
 
Total fixed charges                       $  2,300  $  2,045   $ 2,774  $  2,593  $  2,908  $  2,374  $  1,597
                                          ========  ========  ========  ========  ========  ========  =========
Ratio of earnings to fixed
   charges                                    1.41      1.53      1.53      1.44      1.42      1.41      1.38
                                          ========  ========  ========  ========  ========  ========  =========
</TABLE>
For purposes of computing the consolidated ratio of earnings to fixed charges
"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 (including interest on deposits)
and the proportion deemed representative of the interest factor of rent expense,
net of income from subleases.