How do I calculate any late payment and interest penalties?

I have an amended return with updated amount of tax owed. I need to calculate a late payment and interest penalties amount.

posted

No ... just pay the balance due on the 1040X when you file the return and the IRS/state will send you a bill if needed once they process the return.

Interest doesn't stop until the IRS actually receives the overdue amount from you. At that time they will figure any additional monies owed and will bill you separately for that. They'll send the bill to the mailing address you specified on your return.