Try the following:
=date(year(A1),month(A1)+B1,day(A1))

Given your example, you may need this:
=date(year(A1),month(A1)+B1-1,day(A1))
"viktor" wrote in message
...
hi,

how can i calculate the end date(mm/yyyy) betwen one cell where i have a
date(dd/mm/yyyy) and in another cell i have a number of month(12)

ex: A1: 01/01/2005 B1: 12 in C1 i should obtain 12/2005

Thanks