You can use negative numbers with WORKDAY. For example

=WORKDAY(delivery_date,-1*number_of_days,holidays)


--
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com



"Skip2Maloo" <cabinc@gmail.com> wrote in message
news:1154024066.828497.191940@p79g2000cwp.googlegroups.com...
> Hi all,
>
> We schedule our projects backwards... we have contracted
> completion
> dates and must work backwards from there to determine a start
> date. We
> can closely approximate the number of days each project would
> take us,
> so this is an example of what I need:
>
> Delivery Date - Number of Days = Start Date
>
> The problem I'm having is that the "Number of Days" needs to be
> "Number
> of WORKING days" to exclude weekends and holidays so that when
> that
> number is subtracted from Delivery Date is gives us a correct
> Start
> Date. The paradox is that to use the WORKDAYS or NETWORKDAYS
> function
> we already need to know the Delivery Date and Start Date, the
> latter of
> which hasn't been computed yet. I hope this makes sense, but
> here's an
> example how I need it to work:
>
> (input) Delivery Date: 07/21/06
> (input) # of Days: 15
> (computed) Start Date: 07/03/06
>
> If we entered it in just as you see it, the Start Date would
> actually
> compute to 07/06/06, not 07/03/06. We need to tell it to count
> backwards 15 WORKING DAYS, but I can't figure this one out. I
> suppose
> if I spent a couple days on it I might come up with a
> questionable
> formula, but I was just wondering if anyone out there had a
> more
> elegant solution.
>
> Thanks.
>
> p.s. And no... MS Project won't work for us
>