<PAGE>
 
                                                                    EXHIBIT 11.1


                   CALCULATION OF NET INCOME PER COMMON SHARE
                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
                                  (UNAUDITED)

<TABLE>
<CAPTION>
 
 
                                                                            For the three              For the nine    
                                                                            months ended               months ended          
                                                                            September 30,              September 30,    
                                                                          1996            1995       1996            1995        
                                                                         -------       -------     ------          ------   
<S>                                                                      <C>        <C>           <C>             <C>              
                                                                                                                             
Net income (loss)............................................            $ 2,838     $  (1,852)   $11,789         $ 2,218    
                                                                                                                             
Dividends paid on preferred stock............................                  -          (718)    (1,531)           (718)   
                                                                         -------       -------    -------         -------    
                                                                                                                             
Amount available to common shareholders......................            $ 2,838      $ (2,570)   $10,258         $ 1,500
                                                                         =======       =======    =======         =======    
                                                                                                                             
Weighted average number of common shares outstanding.........             32,025        27,999     30,695          29,207 
                                                                         =======       =======    =======         =======    
                                                                                                                             
Net income (loss) per common share..........................             $  0.09      $  (0.09)   $  0.33         $  0.05    
                                                                         =======       =======    =======         =======     
 
</TABLE>

           CALCULATION OF WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
                                 (IN THOUSANDS)
                                  (UNAUDITED)
<TABLE>
<CAPTION>
 
                                                                            For the three              For the nine
                                                                            months ended               months ended
                                                                            September 30,              September 30,
                                                                            1996         1995        1996          1995
                                                                          ------       ------       -----        ------
<S>                                                                       <C>          <C>          <C>          <C>
Shares outstanding from beginning of period.................              28,704       27,912      28,150        27,722
 
504 and 1,058 stock options and warrants
   exercised in the three and nine months
   ended September 30, 1996,
   respectively.............................................                 210            -         380             -
 
166 and 356 stock options exercised in
   the three months and nine months
   ended September 30, 1995,
   respectively.............................................                   -           87           -           150
 
1,845 common shares issued in conversion
    of preferred stock, July 25, 1996.......................               1,344            -         451             -
 
Common stock equivalents of
    stock options and warrants/1/...........................               1,767            -       1,714         1,335
                                                                          ------       ------      ------        ------
                                                                          32,025       27,999      30,695        29,207
                                                                          ======       ======      ======        ======
</TABLE>
/1/  The calculation of common stock equivalents of stock options and warrants
     is based on the "Treasury Method" as detailed in Accounting Principles
     Board Opinion No. 15.