Yeah, there are a few threads on the topic of date differences. The script I did (in the second link Kelder gave) adds months and years accurately, so it could be used with the $ctime/$asctime method. I showed how to do that in yet another thread on the issue at one point...

Here's that other thread:
Date ranges

In that link, either look down to see either the example with the two $ctime(date)'s in it, or look in the following post that shows an alias example.

Both would, of course, need my $DateXpander script that the last post in the second link from Kelder above has links to.