If you are talking about 7-day weeks, then simply subtract 7 times the
number of weeks from your end date. If you are talking about 5-day weeks,
then use the WORKDAY function (which requires the Analysis ToolPak Add-In)
with -5 times the number of weeks as the number of days. So, assuming your
start date is in A1 and the number of weeks is in B1, then...

For a 7-day week: =A1-7*B1

For a 5-day week: =WORKDAY(A1,-5*B1)

The WORKDAY function allows you account for holidays, so you may want to
look at its help files.

--
Rick (MVP - Excel)


"Richard" wrote in message
...
I am looking for a formula that would allow me to enter an end date for a
project and the number of weeks it would take to complete and these
numbers
would automatically populate a 52 week spreadsheet by filling the
appropriate
cells with color going back in time to give me a start date. for example
if I
had a completion due date of July 17th and it was supposed to take 16
weeks
to complete when would I need to start?