everything is easy when subtracting/adding days
somebody should get in touch with your audit/legal/standards & practices/...
to know/understand/made aware/... of the rules for months/year related computation
whenever the resulting month has a different number of days
but it is strange that in AD 2014 You are the first in Your organization to face the problem
why not ask Your peers if there are already general use functions/subroutines in place ?
why did You add a db2/sql dependency to Your process ???
When I tell somebody to RTFM or STFW I usually have the page open in another tab/window of my browser,
so that I am sure that the information requested can be reached with a very small effort