if you want the cell to stay blank then you could use the following formulae:

=If(c5="","",sum(c4,c5))

"New Excel User" wrote:

I'm trying to create a formula (for example):
In cell D5 I want it to add C4+C5. I would like it to work only after there
is data in C5, but not before. How can I get it to work only when there is
data in C4 & C5? Right now its showing what I have in C4.