=SUM(IF(A2:A300,A2:A30))

This is an array formula. Hit ctrl-shift-enter instead of enter. If you do it
correctly, excel will wrap curly brackets {} around your formula. (don't type
them yourself.)

Adjust the range to match--but you can't use the whole column.

===
Or not entered as an array formula:
=SUMPRODUCT(--(A2:A300),(A2:A30))

(Still can't use the whole column, though.)

LD6892 wrote:

How do I omit a cell that contains a negative number in an addition formula?
I can't use sum because there are cells in between.

--

Dave Peterson