Per Diem Calculation Portal: Calculate Per Diems Free & Online

Per diem claims are simple in principle and fiddly in practice: full days at one rate, partial days at a fraction, and a total that must match the funder’s rules exactly. This free calculator does the arithmetic for full and partial days, so the total is right even when the trip is not a neat number of days.

What the tool does

You enter the number of full days, the number of partial days, the daily rate, and the fraction paid for a partial day, and the tool returns the total with its breakdown shown. The breakdown matters: a total without its working is hard for a finance officer to check, while a total that shows five full days plus two half days at the rate is checkable in seconds. The tool is a calculator only, framed as such, and it applies no funder’s rules beyond the numbers you enter.

How to use it

Count full days as days entirely away, and partial days as travel days or part days, following your funder’s definitions, not your own sense of a long day. Choose the partial-day fraction your funder specifies, commonly 50 percent, and enter the daily rate in the currency of the grant. Press the button, read the breakdown, and compare the total against any cap in the grant terms before claiming. If the funder caps the total, claim the capped amount, not the calculated one, and note the cap in your report.

Worked example

A trip has five full days and two partial days at a daily rate of 60, with partial days paid at 50 percent. The calculation is five times 60, which is 300, plus two times 60 times 0.5, which is 60, giving a total of 360. Change the partial fraction to 75 percent and the total becomes 390. That thirty-unit difference is exactly why the fraction must come from the funder’s terms: guessing it changes the claim by more than a rounding error.

Reading the results honestly

The breakdown is the honest part of the result. If a finance officer questions your claim, the breakdown shows your working, and any error will be visible in it rather than hidden in a single number. Watch for the common mistakes: counting travel days as full days, using the wrong currency, or applying a fraction your funder does not allow. When in doubt, claim the lower defensible amount and ask the funder, since an overclaim creates more trouble than a small underclaim.

Honest limits

This tool multiplies the numbers you give. It does not know your funder’s rates, caps, exclusions, or receipt requirements, and it cannot decide whether a day counts as full or partial under a specific grant. Some funders exclude the first or last travel day, cap meals separately, or require receipts above a threshold; none of that is in this calculator. Always read the grant terms, and treat this total as a draft to check, not a claim to submit blindly.

Practical tips

Keep a one-line diary of each trip day, marking it full or partial as you go, so the claim is built from a record rather than from memory at the end. Save the funder’s per diem page with the claim, since rules change and a claim questioned months later needs the rules that applied at the time. If you travel often, keep a personal table of rates by funder, updated annually.

When rates differ by location

Many funders pay different daily rates by city or country, and a trip visiting two locations needs two calculations, not one average. Split the trip by location, calculate each part with its own rate and fractions, and add the parts, showing each location’s breakdown separately in the claim. A single blended rate looks simpler but invites questions, since the finance officer cannot verify it against any published rate. When a location changes mid-trip, record the change date, because the day of travel between locations is the day most often disputed.

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