Hi CJ

Another way assuming your data is in A1 to A30
then in B30

=IF(A30="","",SUM(A1:A30))
and drag it down as far as you need. The cell references
will update as you drag drown.
i.e. B31 will show =IF(A31="","",SUM(A2:A31)) etc.

The B column will stay blank until you put a value into A

HTH
Martin