I am new to zoho creator and not sure about how to do the following with deluge script . In the Point of Sale application and I want to auto calculate the "Expiry Date" of each item added within the subform based on the invoice date. 

Expiry Date = Invoice Date + X months

In Add_Product Form, i have added a field called Validity

Product Name       Validity(Months)

4 Lessons                   3

5 Lessons                   4

8 Lessons                   5

Thank you for your suggestion!