By the Day: The History and Logic of the Per Diem

Grant travel budgets often reimburse a fixed daily allowance — a per diem — rather than actual receipts. This tidy arrangement, whose Latin name simply means “per day,” has ancient roots and a compelling logic: it simplifies both budgeting and bookkeeping while sparing everyone the tyranny of the itemized receipt.

An Ancient Idea

Paying a set amount per day is very old. Armies, officials, and travelers have long been given a daily allowance to cover their expenses on the road rather than accounting for every meal and bed. The very phrase — Latin for “per day” — reflects how deeply the concept is embedded in the history of sending people to work away from home.

Why Not Just Use Receipts?

Reimbursing actual receipted expenses seems fairer, but it is administratively painful: travelers must save every receipt, and finance staff must scrutinize each one. A per diem cuts through this. By granting a fixed sum per day, it removes the need to track and verify countless small expenses, trading perfect precision for enormous savings in effort on both sides.

Published Rates

Many funders, especially government agencies, require travel to follow published per diem rate schedules that vary by location — higher in expensive cities, lower in cheaper ones. These standardized rates make budgeting straightforward and reimbursement predictable: a traveler knows in advance what a trip will yield, and the funder knows exactly what it will pay, with no surprises at the end.

Building the Estimate

A travel budget combines the per diem — travelers times days times the daily rate — with transportation like airfare, which varies and must be estimated separately. Getting these figures right at the proposal stage avoids later budget revisions, particularly for airfare, which can swing significantly. The humble per diem keeps the largest, fiddliest part of travel cost clean and predictable.

Estimating Travel

To build a travel budget, use the Grant Travel Budget (Per Diem) Calculator. Fold it into a full budget with the Program Budget Calculator, and split an award across categories with the Grant Budget Calculator.