
<PAGE>
 
                    SEI INVESTMENTS COMPANY AND SUBSIDIARIES
                    ----------------------------------------

                  EXHIBIT 11 - EARNINGS PER SHARE CALCULATION
                  -------------------------------------------

                   FOR THE THREE-MONTH PERIOD ENDED JUNE 30,
                   -----------------------------------------


<TABLE>
<CAPTION>
                                                                       1997         1996
                                                                    -----------  -----------
<S>                                                                 <C>          <C>
Earnings per common and common     
  equivalent share (Primary EPS):  
                                   
  Net income                                                        $ 5,141,000  $ 4,893,000
                                                                    ===========  ===========
                                   
  Weighted average number of       
  shares issued and outstanding                                      18,494,000   18,665,000
                                   
  Dilutive effect (excess of       
  number of shares issuable over   
  number of shares assumed to be   
  repurchased with the proceeds,   
  using the average market price   
  during the period) of            
  outstanding options                                                   673,000      861,000
                                                                    -----------  -----------
                                   
  Adjusted weighted average number 
  of shares outstanding                                              19,167,000   19,526,000
                                                                    ===========  ===========
                                   
  Earnings per common and common   
  equivalent share                                                  $       .27  $       .25
                                                                    ===========  ===========
</TABLE>



                                      23
<PAGE>
 
                    SEI INVESTMENTS COMPANY AND SUBSIDIARIES
                    ----------------------------------------

                  EXHIBIT 11 - EARNINGS PER SHARE CALCULATION
                  -------------------------------------------

                   FOR THE THREE-MONTH PERIOD ENDED JUNE 30,
                   -----------------------------------------


<TABLE>
<CAPTION>
                                                                       1997         1996
                                                                    -----------  -----------
<S>                                                                 <C>          <C>
Earnings per common and common                             
  equivalent share, assuming full dilution                 
  (Fully diluted EPS):                                     
                                                           
  Net income                                                        $ 5,141,000  $ 4,893,000
                                                                    ===========  ===========
                                                           
  Weighted average number of                               
  shares issued and outstanding                                      18,494,000   18,665,000
                                                           
  Dilutive effect (excess of                               
  number of shares issuable over                           
  number of shares assumed to be                           
  repurchased with the proceeds,                           
  using the higher of the average market price             
  or ending price during the period) of                    
  outstanding options                                                   850,000      861,000
                                                                    -----------  -----------
                                                           
  Adjusted weighted average number                         
  of shares outstanding, assuming full dilution                      19,344,000   19,526,000
                                                                    ===========  ===========
                                                           
  Earnings per common and common                           
  equivalent share, assuming full dilution                          $       .27  $       .25
                                                                    ===========  ===========
</TABLE>


                                      24
<PAGE>
 
                    SEI INVESTMENTS COMPANY AND SUBSIDIARIES
                    ----------------------------------------

                  EXHIBIT 11 - EARNINGS PER SHARE CALCULATION
                  -------------------------------------------

                    FOR THE SIX-MONTH PERIOD ENDED JUNE 30,
                    ---------------------------------------


<TABLE>
<CAPTION>
                                                                       1997         1996
                                                                    -----------  -----------
<S>                                                                 <C>          <C>
Earnings per common and common                                 
  equivalent share (Primary EPS):                              
                                                               
  Net income                                                        $ 9,942,000  $10,686,000
                                                                    ===========  ===========
                                                               
  Weighted average number of                                   
  shares issued and outstanding                                      18,513,000   18,587,000
                                                               
  Dilutive effect (excess of                                   
  number of shares issuable over                               
  number of shares assumed to be                               
  repurchased with the proceeds,                               
  using the average market price                               
  during the period) of                                        
  outstanding options                                                   703,000      918,000
                                                                    -----------  -----------
                                                               
  Adjusted weighted average number                             
  of shares outstanding                                              19,216,000   19,505,000
                                                                    ===========  ===========
                                                               
  Earnings per common and common                               
  equivalent share                                                  $       .52  $       .55
                                                                    ===========  ===========
</TABLE>



                                      25
<PAGE>
 
                    SEI INVESTMENTS COMPANY AND SUBSIDIARIES
                    ----------------------------------------

                  EXHIBIT 11 - EARNINGS PER SHARE CALCULATION
                  -------------------------------------------

                    FOR THE SIX-MONTH PERIOD ENDED JUNE 30,
                    ---------------------------------------


<TABLE>
<CAPTION>
                                                                        1997         1996
                                                                     -----------  -----------
<S>                                                                  <C>          <C>
Earnings per common and common                    
  equivalent share, assuming full dilution        
  (Fully diluted EPS):                            
                                                  
  Net income                                                         $ 9,942,000  $10,686,000
                                                                     ===========  ===========
                                                  
  Weighted average number of                      
  shares issued and outstanding                                       18,513,000   18,587,000
                                                  
  Dilutive effect (excess of                      
  number of shares issuable over                  
  number of shares assumed to be                  
  repurchased with the proceeds,                  
  using the higher of the average market price    
  or ending price during the period) of           
  outstanding options                                                    880,000      918,000
                                                                     -----------  -----------
                                                  
  Adjusted weighted average number                
  of shares outstanding, assuming full dilution                       19,393,000   19,505,000
                                                                     ===========  ===========
                                                  
  Earnings per common and common                  
  equivalent share, assuming full dilution                           $       .51  $       .55
                                                                     ===========  ===========
</TABLE>




                                      26
