Calculate Due Dates, excluding Holidays and Weekends

The formula is WORKDAY( [start date], [number of days], [holidays] ) this assumes M-F are workdays

I am also attaching a handy table of holidays I created.  You just need to add or delete the 'x' above the holiday to include or exclude that holiday from the list of holidays:

so with that you can use 

=WORKDAY( A1, 7, Holidays)

EDIT - just saw your f/u note and that is because Excel is not counting the start day.  If start on Day 1 and you add 7 days you don't get day 7 you get day 8.  So you have a few options:

simply add 6 workdays instead of 7. this will work if you are always starting on a workday.  If your start date is a weekend or holiday then it will be off

alternatively you could

=WORKDAYS( A1,7, Holidays) -NETWORKDAYS(A1, A1, Holidays)

and that should account for those weekends and holidays