how to set expired password date in databse in mvc

Question

hi to all,

              Here i using this code to compare current date and expired password date

                                  if (DateTime.Now > userObject.PasswordExpiredDate)
                                              return RedirectToAction("PasswordChange", "Index");

           

                       i want to change 30 days once to change the password. now i want to save expired password date in database how to i save it kindly help me
FOR EXAMPLE:
Let consider here i create user 1.6.2014 but i want to save in database 1.7.2014 then only i  should compare current date and expired date can you tell how to do?