Per Diem Calculator
Calculate a business trip's total per diem allowance, with the reduced first and last travel day rate, and compare it against actual spending.
GSA rate for the destination, or your employer's flat rate
GSA standard is 75% on partial travel days
What this calculator does
Trip length, the daily per diem rate, the reduced rate applied to the first and last travel day, and your actual daily spending go in. It returns the total allowance, total actual spend, and the net difference — what you keep if the allowance exceeds spending, or come up short if it doesn’t.
Why the math isn’t just “days times rate”
A naive per diem total multiplies trip days by the daily rate, but that overstates the real allowance for any trip longer than a single day. The first and last calendar days of a trip are travel days, not full days at the destination, and the federal GSA convention — widely adopted by private employers too — pays those two days at a reduced percentage, commonly 75%, of the full rate. A five-day trip is really three full days plus two reduced ones, not five full days.
Flat allowance versus receipt-based reimbursement
Two very different systems both get called “per diem,” and it matters which one applies to you. A flat allowance pays the same fixed amount regardless of actual spending — spend less, keep the difference; spend more, absorb it yourself. A receipt-based system instead reimburses actual documented spending up to a daily cap, with no benefit to spending less and no penalty (up to the cap) for spending more. This calculator models the flat allowance version, which is the one where the net-to-traveler figure actually means something — under a receipt system, that net is always zero by design, since you’re only ever reimbursed what you spent.
Where the GSA rate comes from, and why it varies by city
The federal per diem rate for meals and incidentals varies by destination, reflecting real cost-of-living differences between, say, a small town and a major metro area — the standard rate applies to most of the country, with higher published rates for a list of higher-cost destinations updated annually. Whether your employer uses the exact GSA figure for your specific destination or a simpler flat company-wide rate changes what number belongs in this calculator, so confirm which applies before relying on the result for expense reporting.
For the total cost of a trip beyond meals and incidentals, the road trip cost calculator or family vacation budget covers lodging and transport, and the travel insurance value calculator is worth checking for any trip with meaningful non-refundable costs at stake.
How this is calculated
full days = trip days − 2 allowance = (full days × daily rate) + (2 × daily rate × first/last day %) net to traveler = allowance − actual spend
Frequently asked questions
- Why are the first and last day paid at a reduced rate?
- Because a travel day rarely covers a full day of meals and incidentals at the destination — you might arrive at dinnertime or depart before breakfast. The federal GSA standard reduces the first and last day to 75% of the full daily rate to reflect that, and many employer policies follow the same convention.
- Do I get to keep unused per diem?
- Under most per diem policies, yes — the allowance is a fixed amount regardless of actual spending, which is the incentive built into the system. Some employer policies instead require receipts and only reimburse actual cost up to the daily cap, so check your specific policy before assuming a flat allowance applies.
- What per diem rate should I use?
- The GSA publishes standard and destination-specific daily rates for federal travel, which many private employers also reference or adopt directly. If your employer sets its own flat rate instead, use that — it's the number that actually determines your allowance regardless of what the government rate happens to be for that city.
- Does per diem cover lodging too?
- Under the GSA system, lodging is typically a separate, destination-specific rate from the meals-and-incidentals rate this calculator models — check whether your trip's total allowance is meals-only or includes a lodging component before comparing it against total spending.