How to Calculate Per Diem for a Business Trip

Calculating per diem is four steps once you know the rules. Here's the whole process for a typical multi-day trip.

1. Look up the destination rate

Find the GSA lodging and M&IE rates for the city you're visiting. If the city isn't separately listed, use the standard CONUS rate ($110 lodging / $68 M&IE for FY2026). Lodging can change by month in seasonal destinations, so use the rate for the month you'll travel.

2. Count nights and days

Lodging is paid per night — a trip that arrives Monday and leaves Wednesday is two nights. M&IE is paid per day, including both travel days.

3. Apply the 75% rule to M&IE

Pay 75% of the M&IE rate on the first and last day and 100% on every full day in between.

4. Add it up

• Lodging = nightly rate × number of nights (using each night's month).
• M&IE = (first day 75%) + (full days × 100%) + (last day 75%).
• Total per diem = lodging + M&IE.

That's exactly what PerDiemWise does — pick a city and dates and it returns the itemised, day-by-day total using the real GSA FY2026 figures.