Currently, I have formulas in various cells that looks like this:

=IF($A$2<"",($E$8-$F$7),"")

F7 ($F$7) has a calculation based on a percentage. I've run into the
difficulty is that I need to decide in some cases to not use that
calculation and to have an adjusted value instead.

Is there a way to have the above formula take the value of F7 only if, say,
F8 (a cell we can put a value into) is empty? So, to explain it another
way, if F8 has a value the user has put in, the formula subtracts that
instead?

Tx.