This guidance is consistent with the rules set forth in various IRS revenue procedures, such as Rev. Proc. 2011-47 and Rev. Proc. 2019-48, and Pub 463 which provide detailed rules on the use of per diem rates for substantiating travel expenses.

Proration of the Federal Per Diem or M&IE Rate (Rev. Proc. 2019-48 Sec .04)

Under the Federal Travel Regulations, in determining the federal per diem rate or the federal M&IE rate for the full applicable federal M&IE rate is available for a full day of travel from 12:01 a.m. to 12:00 midnight.

For purposes of determining the amount deemed substantiated for a reimbursement for lodging, meal, and incidental expenses for partial days of travel away from home, either of the following methods may be used to prorate the federal per diem rate or the federal M&IE rate for the partial days of travel:

Method 1: The rate may be prorated using the method prescribed by the Federal Travel Regulations for meal and incidental expenses for partial days, by allocating three-fourths of the applicable rate to each partial day of travel

Example Method (1) – Assume for this example that the standard meal allowance for a full day is $79

Saturday (Day of Departure):The taxpayer departed from Nashville at 6:15 a.m. and arrived in Philadelphia for a 1 p.m. appointment.For the day of departure, the taxpayer can claim 3/4 of the standard meal allowance.Calculation: (3/4 times $79 = $59.25)

Sunday (Full Day in Philadelphia): The taxpayer had an appointment at 1 p.m. and was scheduled to fly home at 6:33 p.m.The flight was delayed, and the taxpayer did not arrive home until 1:30 a.m. Monday. For the full day in Philadelphia, the taxpayer can claim the full standard meal allowance.Calculation: ($79)

Monday (Day of Return):The taxpayer arrived home at 1:30 a.m. Monday. For the day of return, the taxpayer can claim 3/4 of the standard meal allowance. Calculation: (3/4 times $79 = $59.25)

Therefore, the total amount the taxpayer can claim for the standard meal allowance for this trip is $197.50 (59.25 + 79 + 59.25).

Method 2: The rate may be prorated using any method that is consistently applied and is consistent with reasonable business practice. For example, if the taxpayer travels away from home from 9 a.m. one day to 5 p.m. the next day, a method of proration that results in an amount equal to two times the federal M&IE rate is consistent with reasonable business practice (even though the Federal Travel Regulations allow only one and a half times the federal M&IE rate).