You can do this:


C2 = IF(OR(A2="",B2=""),"",SUM(A2:B2))

A3 = IF(C2="","",C2)

then you just copy the formula down.

P.S. I would personally avoid using IF for trivial condition like that since it can get messy when you nest an IF inside another IF, but this one seems simple enough.

Thanks for your reply. This exercise is to determine a way to do a simple horizontal addition problem where, for example, a current expense would be entered in cell B2 that would be added to the previous total expenditures which would be located in A2. We'd like the sum of the two to automatically appear in cell C3, by simply tabbing into it. We'd also like that total to also automatically appear in cell A3 where it would become the new "total expenditure", and it would be added to the next expense....and so on.

Thanks Mr. Onion. That accomplished what we were trying to do! It might take a while to digest what you've suggested, but now we have a place to start.