Can I use variable in Numbers cell formula?
I think that the best solution would be to just assign your variable formula to a different cell and refer to that one in your main formula.

Example:

Cell A1:

=5−SUM(C35:I35)


Cell B1:

IF(A1&gt;0,A1,"")


You could then hide the column where the variable is, so you don't have to see it.