My toolkit consists of:

• Date::Calc
• HTTP::Date (part of libwww-perl)

Date::Calc takes care of most things for me, but I need HTTP::Date to handle those awful string dates used by the HTTP protocol.

For your example, you would probably want to have a look at Delta_days in the Date::Calc module. The link above is to the POD and should tell you what you need to know.

Just as an aside, as a web applications developer, I actually do most of my date crunching in MySQL. Perl tends to just have to do date validation before firing data off to the MySQL stored procedure (or query), with the same functionality duplicated client-side in JavaScript. (The latter cuts down on the rubbish that gets sent to the server. I tend to set a flag and a checksum in JavaScript that tells the server that the input has been pre-validated; Perl then only has to check the checksum before passing the data on down to the database.)

Hope this helps.

Update

Fixed broken links in second list item. I will now write out 100 times "I must check my posts fully before submitting them."