I am trying to write an IF statement in a cell for a calculation based
on whether a cell is blank or not. This is what I have started with
but I know it isn't correct
=IF(ISBLANK(D7),(D6-D2))&IF(ISBLANK(D6),(D5-D2))

Example:

Cell
Weekly Standard 10,000 (D2)
Week 1 Input 2,000 (D3)
Week 2 Input 13,500 (D4)
Week 3 Input (D5)
Week 4 Input (D6)
Week 5 Input (D7)

Variance Amount (D9) (i.e D4-D2)

(This field should be based on the last entry made minus the weekly
standard.
The formula needs to start with Week #5 then 4 then 3 then 2. Any help
with this would be greatly appreciated especially with my limited
knowledge.