By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. It lays out each fee and dollar still due before you completely pay off your mortgage.Here's how it works. Before you send in a check, contact your lender and get a written payoff statement. That statement will include a per-diem interest. It typically details the principal balance, interest due as of that date, per diem, any late fees, etc. What is a Payoff Agreement? A payoff agreement is an informal contract in which a creditor agrees to accept the balance of a debt owed as full payment. Your payoff amount and a good-through date will be displayed in the payoff form. By setting up Auto Pay in MyAccount online or on the GM Financial Mobile app, you can have your payments automatically withdrawn from your bank account.