How about Date::Calc? This allows you to input two different dates and get the difference. I used it for a "Baby Pool" for before my daughter was born (family members could bet on date, weight and gender. Here is a snippet of what I did:

use Date::Calc qw(Delta_Days);

$day_diff{$name} = abs(Delta_Days(2000, $actual_month, $
actual_day, 2000, $guess_month, $guess_day));
[download]

From what I remember, the module was pretty flexible w/ how the date could be input.

Side Note: It appears that there are disagreeing opinions about the module. Test it and see how it fits for you...

bb