You don't need any vba code. Remeber Excel stores dates as numeric values. So, all you need to do is to create formula, like this:
C1 = A1 + B1
, where
C1
is cell, in which formula is stored,
A1
is cell with date,
B1
is cell with number of days
To get more information, read this:
How to use dates and times in Excel[
^]
To calculate end date in VBA, use
DateAdd()[
^] function.