I am trying to allow a user to enter a date and then calculate the month
before.

Eg. Enter in Cell A1 3/31/2009
Cell A2 will calculate automatically 2/28/2009

If Cell A1 is 1/1/2009 then A2 should automatically calculate 12/1/2008 so
that years and leap years are accounted for.

Ultimately I want to be able to calculate the same month in the previous
year but I think I can do this with Month(A1)&"/"&Day(A1)&"/"&Year(A1)-1.

I was trying to find a DateAdd function but can't so I am not sure how to
approach this directly in Excel or should I get into VBA (never really done
this before).

Any help is appreciated TIA rasinc