Can the traveler choose whether or not to use the per diem rate? Per diem is an allowance for lodging, meals, and incidental expenses.The US General Services Administration (GSA) establishes the per diem reimbursement rates. The Payoff Amount and Per Diem Amount quoted herein are effective through December 31, 2020. By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. While in the CONUS, use the Standard CONUS per diem rate. Per diem is a daily amount to cover meal and lodging expenses. You will need to calculate your per diem before the trip. Per Diem Meal Allowed. Breakfast and dinner are the only meals that are reimbursable.