<PAGE>

                                                                      EXHIBIT 11
                           ACT MANUFACTURING, INC.

              Computation of Net Income (Loss) Per Common Share

               Three and Six Months Ended June 30, 1999 and 1998
                     (in thousands except per share data)
                                  (unaudited)

<TABLE>
<CAPTION>
                                                                        Three Months Ended
                                                                        ------------------
                                                                         1999        1998
                                                                        ------      ------
<S>                                                                     <C>         <C>
BASIC NET INCOME PER COMMON SHARE:
    Net income as reported..........................................    $ 2,177     $   86
    Weighted average number of common shares outstanding:
       Common Stock.................................................      9,090      9,063
                                                                        -------     ------
       Basic net income per common share............................    $  0.24     $  .01
                                                                        =======     ======
DILUTED NET INCOME PER COMMON SHARE:
    Net income as reported..........................................    $ 2,177     $   86
    Weighted average number of common shares outstanding:
       Common Stock.................................................      9,090      9,063
       Effect of stock options......................................        363        120
                                                                        -------     ------
          Total.....................................................      9,453      9,183
                                                                        -------     ------
       Diluted net income per common share..........................    $  0.23     $  .01
                                                                        =======     ======
</TABLE>

<TABLE>
<CAPTION>
                                                                         Six Months Ended
                                                                         ----------------
                                                                          1999      1998
                                                                         ------    ------
<S>                                                                     <C>        <C>
BASIC NET INCOME (LOSS) PER COMMON SHARE:
    Net income (loss) as reported ..................................    $ 4,043    $ (1,040)
    Weighted average number of common shares outstanding:
       Common Stock.................................................      9,079       9,063
                                                                        -------    --------
       Basic net income (loss) per common share.....................    $   .45    $   (.11)
                                                                        =======    ========

DILUTED NET INCOME (LOSS) PER COMMON SHARE:
    Net income (loss) as reported...................................    $ 4,043    $ (1,040)
    Weighted average number of common shares outstanding:
       Common Stock.................................................      9,079       9,063
       Effect of stock options......................................        399         ---
                                                                        -------    --------
          Total.....................................................      9,478       9,063
                                                                        -------    --------
    Diluted net income (loss) per common share......................    $   .43    $  ( .11)
                                                                        =======    ========
</TABLE>