Calculate Date by adding numeric field

[VisaManiac]

I have a simple request that I can't seem to locate the right option for the calculation to work.

I just need 3 simple fields.

Due Date + 31 days = New Date

The Due Date & the New Date fields are formated to display as mm/dd/yyyy, and the 31 days field is a numeric read-only field because I don't want this to be changed by the user. I've also set the 'New Date' properties to calculate the SUM of Due Date & 31 days, but I keep getting this pop-up:

"Invalid date/time: please ensure that the date/time exists. Field [NewDate] should match format mm/dd/yyyy."

Also, the NewDate isn't calculating the Due Date + 31 days.

I don't know java so don't know what the script should be plugged in. Any assistance would be greatly appreciated.

Thanks!