By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. Discover more about per diem interest—the daily interest on a loan that occurs outside of the standard repayment period.A 10 day payoff is crucial to getting your old loans paid off during a refinance. Learn how it works from start to finish. Please accept this as my authorization to issue a payoff statement to. Through an effective date of . For general inquires, call 1.800.FULTON. Per diem interest determines your mortgage's interest payments between closing day and the day you start making standard monthly payments. You will have to start over in the right location. Read the instructions carefully before you fill out the forms.