Biff wrote...
Try this:

=DATE(YEAR(C14),MONTH(C14)+30,DAY(C14))
....

Depends on whether the date 30 months from 31-Dec-2005 should be
30-Jun-2007 or 1-Jul-2007. Your formula gives the latter. If the former
is needed, then is't necessary to use something like

=DATE(YEAR(A1),MONTH(A1)+30,0)
+MIN(DAY(A1),DAY(DATE(YEAR(A1),MONTH(A1)+31,0)))