Start with the decision, not the total
A useful travel estimate shows what is known, assumed, and still subject to authorization.
Per diem is not one flat payment. It combines a lodging ceiling with a meals-and-incidental-expenses allowance, commonly called M&IE. The applicable locality, travel dates, meals furnished, lodging actually paid, transportation method, and written authorization can all change the result. MyPerDiem keeps those inputs separate so a traveler can see which assumption moved the estimate.
For CONUS travel, use the temporary-duty location named in the authorization. A nearby ZIP can return a different seasonal lodging ceiling.
Federal per diem uses fiscal-year data, and lodging rates may vary by month even when M&IE does not.
The lodging rate is normally a ceiling. The estimate should use actual lodging when known, limited by that ceiling unless an exception applies.
A government-furnished meal or one included in a registration fee may reduce M&IE. A complimentary hotel breakfast or common-carrier meal generally does not.
Worked example: a four-day CONUS TDY
Assume three lodging nights at an actual cost of $105, a $110 lodging ceiling, and a $68 M&IE rate. Lodging is $315 because the actual nightly cost is below the ceiling. The first and last travel days are $51 each, which is 75% of $68. The two full TDY days are $68 each. Before lodging taxes, transportation, or other authorized expenses, the planning total is $553: $315 lodging plus $238 M&IE.
That example is deliberately simple. Actual expense authority, government quarters, proportional lodging taxes, leave, personal deviations, provided meals, and local business rules can change reimbursement. Use the estimate to prepare questions—not to override an authorization.
GSA per diem rates, GSA M&IE breakdowns, and Joint Travel Regulations.