calculate net working days

Dear all
I would like to calculate net working days in between two dates . I have weekly friday as holidays example

start date : 10-sep-2007
end date : 31-Jan-2008
holidays : every week on friday
calculatate net working days by considering weekly holidays in between above dates. Like this I have around 100 activities in my project

For this I want a simple and straight formula. Infact , I have listed all holidays in columns and against each activity start and end date with the help of formula [ If(and (holiday date => start date, holidaydate <=end date) ,1,0)]and used sum and counted all 1s . All these summed 1s I have deleted from duration between start and end date

Is there any simplified method to this . I request all

The WORKDAY function should do what you want. Excel's help provides good detail about how to use it.

This formula will give you the number of days, excluding Fridays, between a date in A2 and a later date in B2

=B2-A2+1-INT((WEEKDAY(A2-6)+B2-A2)/7)

format formula cell as general

this will include both the start and end dates (assuming they're not Fridays). If you want to exclude the start date change to

=B2-A2-INT((WEEKDAY(A2-5)+B2-A2-1)/7)

Do you just want to exclude Fridays or do you have a list of other holidays to exclude?