General :: Adding Date Add To A Field

i have a tbl that stores items that have an expiry. in a child table i want to store the expiry. but as it is different for each item i need a way of doing this.

i thought that by having

DateAdd('m',3,Date()) in one of the fields this would work.

on click event i would like the date add to come into play but the way i am doing it comes up with an error. too few arguments.

this is what i have so far

Code:
Dim rs As DAO.Recordset
Dim db As DAO.Database
Set db = CurrentDb

[Code].....