|Do you need it exclude Weekends & Holidays?|
Then use the NETWORKDAYS() function which looks like:
So with your Start Date in A1, your End Date in B1
and you list of Holidays is the range C1 thru C10
it would look like:
If you do not need to exclude Weekends or Holidays
then you could use the DATEDIF() function:
The units are "D" Day, "M" Month, ""Y" Year and several others.
or you can do a simple subtraction:
=B1 - A1
Take your pick.