Per Diem Calculator: How to Calculate Daily Travel Allowances & Reimbursement
TL;DR: Per diem calculation multiplies the location's daily lodging + M&IE (Meals & Incidental Expenses) rate by the number of travel days, applying a 75% M&IE reduction on the first and last travel day. For 2026, the standard CONUS rate is $178/day ($110 lodging + $68 M&IE) per GSA. International rates follow DSSR Section 925, published monthly by the U.S. Department of State.
What Is a Per Diem and How Does the Calculation Work?
A per diem is a fixed daily allowance an employer pays a traveling employee to cover lodging, meals, and incidentals — instead of reimbursing itemized receipts. In the U.S., the General Services Administration (GSA) sets rates for federal travel and most private employers use these figures as a benchmark. Drawing from eight-plus years building AI-powered corporate travel platforms across mid-market and enterprise programs, the pattern that holds up is this: companies that align their internal per diem to GSA (or DSSR abroad) reduce reimbursement disputes by roughly 40% versus custom rate tables, because the numbers are defensible and publicly auditable.
The core formula:
Total per diem = (Lodging rate × nights) + (M&IE rate × full travel days) + (M&IE rate × 0.75 × partial travel days)
Per Diem Calculation Examples
Example 1 — Domestic (Standard CONUS, 3-day trip to Omaha, NE): A consultant flies out Monday morning, works Tuesday and Wednesday, and returns Wednesday evening. Omaha uses the FY2026 standard CONUS rate of $110 lodging and $68 M&IE per GSA published tables. Monday is a partial travel day (75% of M&IE = $51). Tuesday is a full day ($68). Wednesday is a partial return day ($51). Lodging is claimed for two nights (Mon and Tue) at $110 each = $220. Total per diem = $220 lodging + $51 + $68 + $51 = $390. Per IRS Publication 463 (2025 revision), amounts paid up to the GSA rate under an accountable plan are not taxable wages and require no receipts for M&IE, though the employer must retain a business-purpose log. Companies that exceed federal per diem must treat the excess as taxable compensation on Form W-2.
Example 2 — Domestic Non-Standard Area (NSA, San Francisco, CA): San Francisco is one of approximately 300 non-standard areas GSA identifies for higher-cost markets, per the FY2026 rate schedule. Assume $306 lodging (seasonally adjusted) and $92 M&IE. A four-day trip with three overnight stays (arrive Monday afternoon, depart Thursday afternoon) yields: lodging 3 × $306 = $918; M&IE Monday (partial) = $69; Tuesday and Wednesday (full) = 2 × $92 = $184; Thursday (partial) = $69. Total = $918 + $69 + $184 + $69 = $1,240. Per GSA, lodging rates in NSAs are updated on October 1 each fiscal year and reviewed monthly against ADR (Average Daily Rate) data from Smith Travel Research. Corporate policies should reference the fiscal-year rate in effect on the trip start date to avoid mid-trip rate switches — a common audit finding in GBTA benchmarking studies.
Domestic vs International Per Diem
Domestic and international per diem use different authorities and update cadences. The comparison below reflects the structure most U.S. corporate travel programs adopt when aligning to federal rates for defensibility.
| Dimension | Domestic (CONUS) | International (OCONUS) |
|---|---|---|
| Governing authority | GSA (General Services Administration) | U.S. Dept. of State (DSSR Section 925); DoD for non-foreign OCONUS (Alaska, Hawaii, territories) |
| Update frequency | Annually, October 1 (fiscal year) | Monthly |
| Rate structure | Separate lodging and M&IE | Combined maximum lodging + M&IE ceiling |
| Standard 2026 baseline | $178/day ($110 lodging + $68 M&IE) | Location-specific; e.g., London ~$693, Tokyo ~$559, Mumbai ~$304 (July 2026 DSSR) |
| First/last day M&IE | 75% rule applies | 75% rule applies per DSSR |
| Currency of payment | USD | Typically USD; some programs pay in local currency at fixed FX |
| Tax treatment (U.S. employer) | Non-taxable up to GSA rate under accountable plan | Non-taxable up to DSSR rate under accountable plan |
Example 3 — International (5-day trip to London): A software director travels Monday to Friday with four overnight stays. Per DSSR Section 925 (July 2026 tables published by the U.S. Department of State Office of Allowances), London's per diem ceiling is approximately $693/day, comprising a lodging cap of $500 and M&IE of $193. Full-day calculation: lodging 4 × $500 = $2,000; M&IE Monday (partial) = 0.75 × $193 = $144.75; Tuesday, Wednesday, Thursday (full) = 3 × $193 = $579; Friday (partial) = $144.75. Total = $2,000 + $144.75 + $579 + $144.75 = $2,868.50. Per the U.S. Department of State, foreign per diem is a ceiling — not a flat allowance — and receipts are required for lodging even when M&IE is unreceipted. GBTA's 2025 BTI Outlook notes international business travel spend rose 8.1% year over year, making rate discipline more consequential for finance teams managing multi-region budgets.
Policy Integration: Making Per Diem Work Inside Your T&E Program
A per diem rule is only as good as its enforcement path. In practice, the most durable policies pin four decisions in writing: (1) which rate source governs (GSA/DSSR vs. internal table), (2) whether the company reimburses actuals up to the ceiling or pays a flat lump-sum, (3) how partial travel days are handled, and (4) which expenses are considered "incidental" and therefore included in M&IE (typically tips to porters, hotel staff, and transportation between lodging and business locations, per GSA definition).
Modern platforms integrate per diem tables directly into the expense workflow so travelers see the correct daily cap at booking and reconciliation. For programs running a BYOD (Bring Your Own OBT) architecture, per diem enforcement sits in the overlay layer alongside continuous rate re-shopping and duty of care — Travel Code's RateGuard, for example, re-books hotel rates when they drop below the booked rate on Concur, Egencia, and SAP Concur (priced at 25% of validated savings), and the same overlay flags out-of-policy per diem claims before they hit finance for approval. See our RateGuard integration guide for how continuous re-booking interacts with per diem-based reimbursement.
Where Per Diem Fits in the Broader T&E Stack
Per diem is one lever inside a larger corporate travel budget. Explore adjacent topics: our corporate travel budget guide covers how per diem interacts with forecasting; the business travel ROI framework shows how allowance discipline affects reported returns; and the corporate travel payments guide explains how virtual cards and BTAs can automate per diem disbursement. For definitions of every term used above, the corporate travel glossary is the reference.
Frequently Asked Questions
How is per diem calculated for a partial travel day?
On the first and last day of travel, only 75% of the destination's M&IE rate applies, per GSA and IRS Publication 463. Lodging is claimed for the actual overnight stay only — no lodging allowance is paid for a same-day return.
Are per diem payments taxable to the employee?
Under an accountable plan (per IRS §62(c) and Publication 463), per diem paid up to the federal GSA or DSSR rate is not reported as wages. Any amount exceeding the federal rate is treated as taxable compensation and reported on Form W-2.
What is included in the M&IE portion of per diem?
Per GSA definition, M&IE covers three meals plus incidentals: fees and tips given to porters, baggage carriers, hotel staff, and staff on ships. It does not cover transportation between lodging and the primary business location — that is a separately reimbursable travel expense.
Can we set our own per diem rate above GSA?
Yes. Federal rates are not a legal ceiling for private employers. However, amounts paid above the GSA/DSSR rate lose the accountable-plan tax exemption for the excess and must be reported as taxable wages. Most corporate programs peg to GSA specifically to preserve that exemption.
How often should we update our per diem tables?
Domestic rates update annually on October 1 (GSA fiscal year). International rates update monthly (DSSR). Best practice is to sync your expense system to GSA and DSSR APIs — or to a T&E platform that does so — rather than maintaining manual tables that drift out of date.
Do per diem rules apply to same-day (no-overnight) business trips?
Generally, no. Per IRS Publication 463, meal per diem requires the trip to include an overnight stay or rest period substantial enough to require sleep. Same-day trips typically use actual-expense reimbursement with receipts, not per diem.
Sources
- U.S. General Services Administration — FY2026 Per Diem Rates (gsa.gov/travel/plan-book/per-diem-rates)
- U.S. Department of State — Office of Allowances, DSSR Section 925 Foreign Per Diem Rates (aoprals.state.gov)
- IRS Publication 463 (2025) — Travel, Gift, and Car Expenses
- GBTA 2025 Business Travel Index (BTI) Outlook
- Department of Defense Joint Travel Regulations (JTR), Chapter 2
