"tonyalt3" wrote:
I would like to calculate how many months it has been
from one cell to another. Example: cell a1 has 1/5/2009
and cell b1 has 5/17/2009.

The correct solution for you depends on how you want to count the month
difference.

One solution:

=datedif(A1,A2,"m")

where A1 has 1/5/2009 and A2 has 5/17/2009.

But note that A1 were 1/18/2009, DATEDIF would result in 3. If you would
prefer 4 still, another solution is:

=(year(A2)-year(A1))*12 + month(A2)-month(A1)

On the other hand, note that the latter solution would return 1 if A1 were
1/31/2009 and A2 is 2/1/2009; that is, "one month" for a single day's
difference. Is that acceptable?