Calculate a new date depends on datepicker with a certain offset of days

Calculate a new date depends on datepicker with a certain offset of days


Hi everyone!
I've got a input field with a datepicker. In another field I have a
integer value (eg. 10). Now I want to calculate a new date with this
offset. I use the datepicker with an own dateform (DD, d. MM yy).
How can I solve this problem?
Thx for help!
Jonathan