Discover more about per diem interest—the daily interest on a loan that occurs outside of the standard repayment period. The first step is to get in touch with your lender or loan servicer.You can find their contact information on your monthly statements. By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. A 10 day payoff is crucial to getting your old loans paid off during a refinance. Learn how it works from start to finish. A payoff letter provides instructions on how to pay off a loan with a lump sum before the loan term ends. Learn how payoff letters work. The new interest calculation applies when an FHA loan with a Note date of January 21, 2015 or after, is paid in full. Before you send in a check, contact your lender and get a written payoff statement.