Rules and data behind each amount

Nothing on this site is an estimate of what travel costs: it is the federal rule applied to the dates and places you enter. This page lists each rule, the text it comes from, how the code applies it, the official figures the tests compare against, and what the tools leave out.

1. GSA rates: two fiscal years, twelve months, every ZIP code

The GSA per diem files are downloaded as published: the FY2026 ZIP file (August 14, 2025), the FY2027 ZIP file (September 3, 2026) and the two rate files that give each area's counties. A script keeps, for every non-standard area, the twelve monthly lodging maximums (October to September) and the M&IE rate, for both years: 301 records. The standard CONUS rate is $113 + $68 in FY2027 and was $110 + $68 in FY2026. GSA lists the Washington, DC area under the District, Maryland and Virginia: the three records carry the same rates.

Search by city uses the Census Bureau's Vintage 2024 population estimates and the 2020 place-by-county file: 2,387 cities of 15,000 people or more are placed in their main county, then in the GSA area that holds most of that county's ZIP codes (Edwards Air Force Base has Kern County ZIP codes in the Los Angeles area; Kern County itself is the Bakersfield area). Areas defined by city limits (Santa Monica, Sedona, Falmouth) match the city name. A ZIP code split between two areas takes the non-standard one, as the GSA lookup does. 40,426 ZIP codes are searchable.

2. The day rules of the Federal Travel Regulation

The subsistence part of the FTR was rewritten by FTR Case 2025-05 (90 FR 56893, December 8, 2025); the sections cited below are the new ones.

• Eligibility (§ 301-11.1): official travel away from the official station, in travel status for more than 12 hours.
• Lodging (§ 301-11.19): actual cost up to the maximum. Each night takes the maximum of its own month and fiscal year. Lodging taxes are reimbursed apart (§ 301-11.16) and have their own field.
• M&IE (§ 301-11.20): 75% on the day of departure and the last day; 100% on full days; one day of more than 12 and less than 24 hours: 75%.
• Provided meals (§ 301-11.21): the GSA breakdown amount is deducted; on the first and last day the full amount comes off the reduced rate; deductions never leave less than the incidental expenses; meals from a common carrier or a free hotel meal are not deducted.

Worked example: Gulf Shores, Alabama, May 30 to June 2, 2027

Three nights straddle a season change: May at $177, June at $221. A conference dinner on the arrival day and a lunch on the next day are provided. The calculator gives $575 of lodging and $208.00 of M&IE, $783.00 in all:

3. Mileage

IRS business, medical, moving and charity rates come from Notice 2026-10 (January 1 to June 30, 2026) and Announcement 2026-11 (from July 1, 2026, "recent increases in the price of fuel"). A mile takes the rate of the day it was driven; the trip calculator uses the departure date. Federal POV rates come from GSA: $0.76 for a car, $0.235 when a government car was available. The depreciation part of the business rate (35 cents in 2026) and the FAVR cost limit ($61,700) come from Notice 2026-10.

4. Tax rules

High-low rates ($329 and $230 from October 1, 2026; $319 and $225 before) and the transportation industry M&IE ($80 in CONUS, $86 outside) come from Notice 2026-60 and Notice 2025-54. Partial days for a deduction use 75% (Rev. Proc. 2019-48, section 6.04(1)); a payor may use 75% or another consistent method. The 80% limit for workers under hours of service and the accountable plan rules come from Publication 463, the 7.5% floor for medical costs from Publication 502.

5. Fuel, electricity and vehicles

Gasoline and diesel: EIA weekly retail prices, week of October 5, 2026 (U.S. regular $4.354). Nine states have their own EIA series; the others take their region (New England, Central Atlantic, Lower Atlantic, Midwest, Gulf Coast, Rocky Mountain, West Coast outside California). Electricity: EIA Electric Power Monthly, Table 5.6.B, residential price year to date through July 2026. Consumption: EPA fueleconomy.gov, combined MPG and combined kWh per 100 miles (energy drawn from the outlet, charging losses included).

6. Tests

Before each release the engine passes tests built from official values: the five first and last day amounts of the GSA breakdown ($51.00, $55.50, $60.00, $64.50, $69.00), a four-day trip at $92 (2 × $69 + 2 × $92), a trip across September 30 (two nights at $110, one at $113), the seasonal Gulf Shores and Jackson figures of the GSA file, the 12-hour threshold, the meal deductions and the $5 floor, the IRS rates on June 30 and July 1, 2026, the GSA example of 100 miles at $0.76, and every row of the GSA OCONUS breakdown from $1 to $265.

7. Limits

• CONUS only for the GSA tables; Alaska, Hawaii, territories and foreign cities are entered by hand from the Department of Defense or State tables.
• No actual expense method, no agency-specific reduced rates for long stays, no conference lodging allowance.
• A city is placed in its main county; a city spread over several counties may have neighborhoods in another GSA area. The ZIP code search is exact.
• Fuel and electricity prices are averages of a week or of seven months; your pump and your utility differ.
• The yearly loss of value of a car, insurance and maintenance are your own inputs: no official table exists.

Corrections: contact page.