Try it this way:
=if(count(a1:a2)=2,a1+a2,"what you want when not filled in")

Regards,
Fred.

"Jon the Contractor" <Jon the wrote in
message ...
If i have a dollar value in cell a1 and no value in cell a2 and the sum
formula in cell a3, a3 returns the value of cell a1 since it is the only
cell
with a value in it. Is there a formula that will sum a1 and a2 only when
they both have values in them?