Plain-language travel rules
Seven distinctions that prevent most bad per diem estimates.
The official regulations are detailed because the facts of a trip matter. This guide explains the distinctions used by the calculator, but it cannot decide entitlement. When the guide and a current official source differ, follow the official source and ask the authorizing or finance office to apply it to the trip.
1. A lodging rate is a ceiling, not automatic income.
Ordinary lodging reimbursement is based on the amount actually paid, limited to the applicable lodging ceiling. A traveler does not normally keep the difference after choosing a cheaper room. Actual-expense authority and contracted or government lodging can change the calculation.
2. M&IE is an allowance with travel-day treatment.
For qualifying travel, the first and last travel days generally use 75% of the applicable M&IE rate. Full days at the TDY location use the applicable full rate before any required furnished-meal deductions.
3. Not every free meal is deductible.
GSA guidance distinguishes meals furnished by the government or included in a registration fee from complimentary hotel meals and meals provided by a common carrier. The latter generally do not affect per diem. Record why a meal is being deducted, not merely that no payment was made.
4. Trip length does not automatically create a 75% or 55% rate.
Current JTR reduced-rate provisions require the responsible authority to establish the reduced rate. Long-term lodging can lower actual daily lodging cost, but the old automatic duration-based flat-rate assumption should not be applied merely because a trip exceeds 30 or 180 days.
5. CONUS and OCONUS use different source paths.
GSA establishes CONUS rates. Foreign-area rates come from the Department of State, while DTMO publishes non-foreign OCONUS rates and military travel guidance. Orders may also establish special conditions that a public rate table cannot show.
6. PCS mileage and TDY mileage are not interchangeable.
TDY mileage is intended to reimburse average POV operating expense. PCS MALT is a different allowance and covers the authorized travelers in the vehicle. The rates and travel-day calculations differ.
7. An estimate can omit an entitlement or include a non-reimbursable cost.
Taxes, fees, parking, tolls, rental-car fuel, dual lodging, leave, personal deviations, constructed travel, government meals, and local rules all require facts the calculator may not have. Treat “other expenses” as a question list for the authorization—not as guaranteed reimbursement.