I have a spreadsheet that I need to increment Column X by one on a monthly
basis. When Column x = 12 then it goes back to 0 and column w is is
incremented by one.

Example:

March 2009
Column W Column X
10 11

April 2009 After Calculation
Column W Column X
11 0

May 2009 After Calculation
Column W Column X
11 1

Can someone give advice on how to best accomplish this?

Thanks in advance.
CB