A 10day payoff refers to the time it takes for your new lender to pay off your old loans during a refinance. It's the payoff amount 10 days in the future.By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. 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 purpose of this Originator's Guide is to describe the Mortgage Credit Certificate. The Payoff Amount and Per Diem Amount quoted herein are effective through December 31, 2020.