Hi!

Assuming your sheets are called Jan, Feb, Mar... etc and the money for
that month is in column H:H (so not in one cell in H), the best way is:

=SUM(Jan:Dec!H:H)

should you have subtotals in Column H - they will be double counted,
so get rid of them...
Another way is to insert two tabs : Start, End name the function
=SUM(Start:End!H:H) and move the sheets you want to have added between
these tabs - a bit kleener....