Depending on how the monthly sheets are set up it could be something as
simple as: =SUM(Sheet1:Sheet12!B4) if the values you want to sum are in
cell B4 on each of the 12 monthly sheets.
The easy way to do the above is to type =Sum( into the cell on your totals
sheet where you want the total. Then click the tab for Sheet1, click cell
B4, then Shift-Click the tab for Sheet12. Close the parens & press return.
If each of the 12 monthly sheets aren't set up with the same layout it's a
bit more work, but no more complex. The basic difference between 3D formulas
& those on the same sheet as the values is that the formula needs to include
the sheet name in addition to the cell reference(s). Using Named Ranges can
make it a lot easier and there are other features as well, such as Data>
Consolidate.
HTH |:>)
Bob Jones
[MVP] Office:Mac