SUM will only sum actual numbers, while the = + + construction will convert any strings that look
like numbers into numbers prior to adding.

So, my guess is that one of your "numbers" is actually a string, either entered in a cell that was
formatted as text, returned as a string from a formula, or entered with a leading single quote.

You can change the SUM formula to

=SUM(H3:J3*1)

entered using Ctrl-Shift-Enter, or use

=SUMPRODUCT(H3:J3*1)

HTH,
Bernie
MS Excel MVP


"Watercolor artist" wrote in message
...
I have a cell (k3) with this formula: =sum(h3:j3). The sum is not correct;
however, when I enter in K3 this formula, =h3+i3+j3, it works. Is this a bug
in Excel? (I'm using Excel 2003.)