Other folk have told you about Tools/ Options/ Calculation/ Automatic, but
another point is that you don't need SUM if you are using C4+C7.

=C4+C7 will do, or you can use =SUM(C4,C7). If you give SUM more than one
parameter, it will add them together, but as you've given it only one
parameter (C4+C7), then it's got nothing to add to that parameter. It's as
unnecessary as saying =PRODUCT(C4+C7) or =AVERAGE(C4+C7) or =MIN(C4+C7) or
=MAX(C4+C7) or ...
--
David Biddulph

"chris" wrote in message
ups.com...
I recently started experiencing a problem I have never had in Excel
before, and I don't know if it has to do with an Excel setting in
general or if I screwed something up with the Macros I was writing.

I have a bunch of formulas in my worksheets (If Statements, Now(),
Sum(), etc). Let me use this quick example.

C4 = 5
C7 = 10
C8 = Sum(C4 + C7)

If I repopulate C4 and C7, C8 no longer automatically changes. But if
I go to edit C8 (click on it and hit F2) and then hit enter, it will
then update correctly.

Why on earth is it doing that?