Searching for a fillable Mortgage Loan Payoff Letter Template? Use our easy editor for PDF files and fill this form out quickly.By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. Add the interest, the principal balance. The new interest calculation applies when an FHA loan with a Note date of January 21, 2015 or after, is paid in full. It typically details the principal balance, interest due as of that date, per diem, any late fees, etc. Discover more about per diem interest—the daily interest on a loan that occurs outside of the standard repayment period. 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. Select one loan in the main window and click Loan > Payoff Calculator on the main menu to open this window.