In addition to the good answer from moritz:

I prefer Date::Calc for all my Date-calculations. It may be overhead in your case, but I like the idea of having only one Date-module to learn ;-) Date::Calc offers a function called Add_Delta_Days which serves your purpose.

HTH, Rata

Update:WOW! I thought I was pretty fast with typing my answer ... but 5 monks were faster! I'm impressed!