Please help with a script that will auto-populate a date field

Hello,

I have a requirement. When I enter an inter value in a field, I want a date field to be updated.

For example, to set the next service date of an item, I want that functionality to update the date field automatically by entering the number of months required for the next service.

so if x is the number of months for the next service, dateField = x + currentDate.

How do I achieve this?

Thanks