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. 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. It typically details the principal balance, interest due as of that date, per diem, any late fees, etc. Please include a per diem amount in the statement. Please email this information to as soon as possible. Federal Per Diem Rate. No. You may only use the actual amount of expenses.