A form to calculate when a term expire

I need a a form to calculate when a term expire (termini processuali). The user enters a date (exsample April 26, 2012) and indicates how many day the term expire (example the term expire in 30 days). The system must indicate the expiration date (in this case the result would be Saturday, May 26, 2012). If the user enters two or three succesive terms (exsample 30 days expire first term + 30 days expires second terms + 20 days expire terd terms) the system must indicate the three dates. In this case, if the starting date is April 26, we obtain: The first 30-day period expires Saturday, May 26, 2012 The second 30-day period expires Monday, June 25 The third 20-day terms espire Sunday, 15/07/2012. In all the above cases the user must select an option to jump the period from 1 August to 15 September (sospensione termini processuali). Another option is to allow the calculation in reverse (for example if I have to deposit a processual act 10 days before May 30, 2012 the result is Sunday, May 20, 2012).