Due date is 6 business days

What kind of formula should I use if I need to setup a due date to be 6 business days from the value in a cell (Q5)?

The simplest way to do this is to use the WORKDAY function from Analysis ToolPak

=WORKDAY(Q5,6) You can also add a holiday range if you want to exclude those too, i.e.

=WORKDAY(Q5,6,holidays) where holidays is a named range containing a list of holiday dates

If you don't have Analysis ToolPak install with Tools > add-ins > tick "Analysis ToolPak".

If you don't have or can't use ATP then, if you always want to add exactly 6 days you could use the formula

=Q5+CHOOSE(WEEKDAY(Q5),8,8,8,8,8,10,9)