Per Diem Calculator

How to use the per diem calculator

Begin with nights away, not a guessed number of travel days. A trip of N nights spans N+1 calendar travel days. Leaving Monday and returning Wednesday means two nights but three days. The engine adds that extra day automatically. Counting two nights as two days removes a payable travel day and always understates the M&IE calculation.

The first and last travel day each receive 75 percent of the applicable M&IE rate under the federal rule. Intervening days receive the full rate. Departure time and return time do not prorate the fraction, so a 6 a.m. departure and a 9 p.m. departure receive the same percentage. The flat rule prevents an hours-based calculation.

A day trip with no overnight is one travel day in this engine and receives the reduced M&IE rate once. It does not receive two reduced allowances merely because the traveler both departed and returned. Federal eligibility rules for short travel still matter, including the more-than-12-hours rule described in the Federal Travel Regulation, so confirm that the trip qualifies before treating the estimate as payable.

1. 1

   Zero nights

   The engine counts one reduced travel day and one 75 percent payment, not separate departure and return allowances for the same calendar day.

2. 2

   One night

   Two travel days are both reduced, producing 150 percent of one full daily M&IE rate before any applicable provided-meal deductions are subtracted.

3. 3

   Two or more nights

   The first and last days are reduced while every intervening calendar day receives the full M&IE rate before qualifying meal deductions are applied.

Enter lodging as two separate numbers: the published cap and the actual room cost per night. The calculator reimburses the lower number for each night. A $90 room under a $110 cap produces $90, not $110. A $130 room produces $110 and leaves $20 per night as estimated excess unless an authorized exception permits more.

Enter provided-meal deductions only after checking the applicable allocation. A conference lunch included in registration is normally deducted, while a complimentary hotel breakfast is not deducted under the cited federal provision. On a 75 percent travel day, subtract the full allocated meal amount rather than 75 percent of that allocation, without reducing the result below the incidental component.

Day counting controls the result

The difficult part of per diem is calendar structure, not finding a rate. Every overnight trip has one more travel day than night because the departure day occurs before the first night and the return day occurs after the last. The error is directional: substituting nights for days always removes allowance rather than accidentally adding it.

For travel lasting at least 24 hours, 41 CFR 301-11.20 applies 75 percent to the departure and return days and 100 percent to intervening days. Travel lasting more than 12 but less than 24 hours receives 75 percent for each calendar day involved. This calculator models a zero-night trip as one reduced day, consistent with its stated input design.

The 75 percent fraction applies only to M&IE. It is a flat travel-day rule rather than an hourly proration. A traveler does not earn more by leaving before breakfast, less by leaving after dinner, or a second allowance by returning on the same no-overnight trip. Eligibility and provided-meal deductions are separate questions applied after the day structure is known.

At a $68 M&IE rate, each reduced day is $51. A one-night trip therefore pays $102 because both travel days are reduced. A two-night trip adds one full $68 day for $170. Every additional night after that creates another intervening travel day at the full rate, so the allowance rises by $68 when no meal deductions apply.

Lodging, meals, and incidentals follow different rules

Under the federal lodgings-plus system, lodging reimburses the actual amount incurred up to the maximum lodging rate unless an authorized exception allows more. Receipts are required. A cheaper room saves the employer money because reimbursement stops at actual cost. A room above the cap can leave the traveler responsible for the difference, which the calculator reports as lodging excess.

M&IE means meals and incidental expenses. Meals include breakfast, lunch, dinner, and associated taxes and tips. They exclude alcoholic beverages and entertainment. Federal incidentals are fees and tips paid to porters, baggage carriers, hotel staff, and ship staff. The term is not a general allowance for laundry, snacks, toiletries, local transportation, or every small purchase made during travel.

M&IE is paid from the applicable allowance rather than limited to itemized meal receipts, although the traveler must still establish the time, place, and business purpose of travel. The lodging ceiling cannot be shifted into M&IE, and an unused meal allowance cannot be shifted into lodging. Combining them too early hides the distinction that controls reimbursement.

A meal furnished by the government or included in a conference registration fee is normally deducted using the official breakfast, lunch, or dinner allocation for the M&IE tier. On the first or last day, subtract the full allocated meal amount from the reduced allowance. The result cannot fall below the incidental-expense portion specified for that rate tier.

The regulation does not deduct a meal supplied by a common carrier or a complimentary meal provided by a hotel or motel. It also recognizes exceptions connected with medical or religious needs and inability to eat the meal for official-business reasons. A conference lunch and a hotel breakfast can therefore produce different treatment even when neither appears as a separate charge.

Rate authorities and tax treatment

GSA sets federal per diem rates for the continental United States. The Department of Defense, through the Defense Travel Management Office, sets rates for non-foreign OCONUS locations, including Alaska, Hawaii, United States territories, and possessions. The Department of State sets rates for foreign locations. Choose the authority before searching by city, county, installation, or country.

For federal fiscal year 2026, from October 1, 2025 through September 30, 2026, GSA’s standard CONUS rate is $110 for lodging plus $68 for M&IE where no locality-specific rate applies. This standard is dated rather than timeless. Locality and seasonal tables can differ, so the calculator requires both rates as inputs instead of storing a nationwide default as permanent truth.

Federal travel rates usually follow the federal fiscal year and locality lodging caps can change by month. The applicable location is normally tied to the temporary duty destination, not whichever nearby place produces the highest figure. Verify the official lookup and travel order for every destination and date. A multistop trip may need separate calculations before combining its totals.

Under an accountable plan, an allowance no greater than the applicable federal rate can be treated as substantiated when the worker accounts for the dates, place, and business purpose. Amounts above the federal rate generally become wages unless excess is returned. A flat allowance with no adequate expense report, or any allowance under a nonaccountable plan, is taxable wages.

The tax rules do not convert a private employer’s policy into the Federal Travel Regulation. A business may choose different reimbursement terms, subject to applicable employment law and contract obligations, while payroll treatment still follows federal accountable-plan requirements. These estimates are not tax or legal advice; confirm current rates, employer rules, agency authorization, and supporting records before submitting or paying a claim.

The formula, worked line by line

The engine first rounds nights to a nonnegative whole number and adds one to obtain travel days. A zero-night trip remains one travel day. One reduced day applies when the trip has only that day; otherwise two reduced days represent departure and return. Full days are the remaining travel days after those reduced days are removed.

Reduced M&IE uses the exact ratio three quarters rather than a binary decimal approximation. The engine multiplies reduced days by the full M&IE rate, applies 3 divided by 4, and rounds to integer cents. It then adds full days at 100 percent and subtracts the provided-meal amount without allowing M&IE to fall below zero.

Lodging runs through a separate path. The engine compares actual nightly cost with the lodging cap and uses the lower amount, then multiplies by nights. When actual cost exceeds the cap, the lodging-excess output reports the difference for all nights. A zero-night trip produces no lodging reimbursement even though it still has one M&IE travel day.

The combined total adds calculated M&IE and reimbursable lodging. That total is useful for estimating payment, but it should not blur the two components. Lodging is actual cost subject to a cap and usually requires receipts. M&IE is a rate-based allowance subject to travel-day percentages, provided-meal deductions, destination rules, and accountable-plan substantiation.

travel days = nights + 1
reduced days = 1 for a day trip, otherwise 2
full days = travel days − reduced days
M&IE before deductions = full days × rate + reduced days × rate × 3/4
M&IE = maximum of zero and M&IE before deductions − provided meals
lodging = nights × minimum of actual nightly cost and nightly cap
total = M&IE + lodging

Provided-meal deductions enter as one combined amount in this engine. Determine that amount outside the calculator using the official allocation for each breakfast, lunch, or dinner and the applicable exception rules. On reduced travel days, use the full allocated meal value rather than reducing the meal value to 75 percent before subtracting it.

Because meal deductions cannot reduce the federal allowance below the incidental-expense component, a user should not enter a raw deduction that violates that floor. The calculator prevents a negative M&IE result but does not know the incidental allocation for the selected tier. Check GSA’s breakdown and calculate the permitted aggregate deduction before entering it.

The engine calculates arithmetic, not eligibility. A no-overnight trip can require more than 12 hours of qualifying travel under the cited federal rule, and private policies may use another threshold. The travel order, agency rules, destination, provided meals, special lodging authorization, and accountable-plan record all sit outside the five numerical inputs.

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