2 calculations with one populate button

2 calculations with one populate button

I have a simple worksheet that auto populates hours based on key values.
This all works fine. The problem I have now is that I need to add some
form of a contingency column which is a percentage figure of the total
hours used up to this column. Add the contingency figures to the sheet and
carry on with the populate.
Is there anyway i can do the first populate up to the contingency column.
Stop. Get the current value (for total hours) then do some calculations
and then carry on with the auto populate?
I don't really have any code I can share, but any pointers in the right
direction would be extremely useful.
Thankyou for your time.