Month Difference - Function Module needed

Hi Experts,

In my report, I am using mcs0-spmon as select options; one of my inputs where the user will enter month and year in the selection screen . e.g. 04.2008 to 07.2008

I want to calculate the month difference and it should not exceed 3 months. If it does, an error will be shown.

My question is -

Is there any Function Module by which I can proceed. How do I go about it?

Can anyone tell me a solution?

Thanks in advance