per diem calculation wrong for partial days error

TL;DR

Most policies pay a reduced rate (commonly 75 percent) for the first and last travel days. Check your company's partial-day rule, confirm the trip's departure and return times are accurate, and recalculate; the usual error is full days counted where partial days apply.

Error

per diem calculation wrong for partial days

Steps

1. Look up your company's per diem policy for partial days (first/last day percentage). Expected: you know the exact rule, for example 75 percent.
2. Verify the trip's departure and return times in the expense tool. Expected: the timestamps reflect actual travel, not midnight defaults.
3. Recompute by hand: full days at 100 percent plus first and last days at the partial rate. Expected: a number you can compare against the tool.
4. Correct the timestamps if they are wrong and trigger a recalculation. Expected: the tool's total now matches your hand computation.
5. If the tool still disagrees, check whether it counts travel days by calendar date or by 24-hour periods. Expected: you find the counting convention causing the gap.

When to use

• The per diem total is off by roughly one daily rate on a multi-day trip.
• Travel started or ended mid-day.

When not to use

• No per diem calculated at all (check timestamps and rate configuration).
• The daily rate itself is wrong (ask the admin to fix the rate table).

Tool compatibility

• Rydoo, Concur, Expensify per diem modules; policy rules per company.

Variant phrasings

Partial day per diem incorrect

Same problem, shorter wording.

First and last day per diem wrong

Names the affected days directly.

Why it happens

Per diem tools apply the partial-day rule to the trip's boundary days. Wrong timestamps (midnight defaults) or a misunderstood rule (full day vs 75 percent) shift the total by a large, noticeable amount.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstvn26RiU1e1oQUE2lhZkMw