Need help subtracting workdays from a date

Hey all,

I’m trying to set up internal milestones based on a project’s due date. I’m trying to set them up by planning backwards, subtracting workdays for each milestone.

In this case, the due date for milestone 1 should be 5 workdays before the start date for milestone 2.

Here’s what I have currently:

SUBTRACT_DAYS({Milestone2#Start}, 5)

However, this is subtracting total days, not workdays.

I’ve tried to reverse engineer this but I’ve always been bad with formulas and I have zero idea what I’m doing here. The end result in my head is something like:

SUBTRACT_DAYS({Milestone2#Start}, (formula for 5 workdays))

Does anyone have any thoughts on how to accomplish this? Searches of Google + the forums don’t point me to any formulas for manually calculating the number of workdays.