Advance Copy/Paste Row Data

 Well welcome to the club. I have been using QuickBase since 2002 and I still think it's the greatest thing ever invented. But it keeps getting better every month with new releases a new features.

What you were looking for is very easy to do. You will use a feature called automations. The trigger for the automation will be when the record is  edited and is flagged as being completed.

So it's very easy to have the automation create a new record when that happens but the issue is that your trigger record, i.e. the one that was completed, needs to have the information as to where the next due date is.

So that is just a matter of creating a formula for the formula date field so the completed record knows when it successor record is due.

There are a whole variety of date functions, but one that you will find useful is

AdjustMonth([Due Date], n)

where n is the number of months to adjust 

Feel free to post back if you need help with the formula for the next due date.