Per Diem Tax Rules: Requirements, Federal Rate Ceiling, and Failed Plans

Per diem tax rules turn on one question: is the payment made under an accountable plan and within federal rates? If yes, the money is tax-free to the employee, invisible on the W-2, and deductible to the employer. If no, every dollar becomes taxable wages subject to income tax withholding and payroll taxes, and since 2018 the employee has had no way to deduct the business travel costs that per diem was meant to cover.

That last point is what makes the structure of the plan matter so much. The Tax Cuts and Jobs Act eliminated the deduction for unreimbursed employee business expenses beginning in 2018, and the One Big Beautiful Bill Act made that elimination permanent starting in 2026.¹ So if your employer’s reimbursement setup fails IRS rules, you pay tax on the full per diem as if it were a bonus, with nothing on your personal return to offset it.

The Three Requirements for Tax-Free Per Diem

For per diem to be excluded from your wages, the employer’s arrangement has to qualify as an accountable plan. Three conditions must all be met. Miss even one, and the whole payment converts to taxable wages.

Business connection. The expenses must be ordinary and necessary costs the employee incurs while traveling away from their tax home on business. Your tax home is the city or general area of your main place of business, not necessarily where your family lives. The assignment also has to be temporary, realistically expected to last a year or less; once it stretches past a year, the new location becomes your tax home and per diem treatment disappears.²
Adequate accounting. The employee has to document the dates, locations, and business purpose of each trip and submit that to the employer within a reasonable period. The IRS safe harbor treats substantiation within 60 days of the expense as timely. Flat per diem doesn’t excuse you from proving when and where the travel happened.³
Return of excess. Anything paid above the substantiated expenses or the applicable federal per diem rate must be paid back to the employer. The safe harbor gives the employee 120 days from when the expense was incurred to return excess funds.³

The regulations don’t strictly require a written plan document, but running the arrangement without one puts the employer on shaky ground in an audit. A written policy that spells out substantiation deadlines and excess-return rules gives everyone something concrete to point to.

When Per Diem Exceeds the Federal Rate

An employer can pay above the federal per diem rate and still keep most of the payment tax-free, as long as the accountable plan rules are otherwise satisfied. Only the excess over the federal rate is taxable. On the W-2, the substantiated portion goes into Box 12 under Code L, while the excess flows into Boxes 1, 3, and 5 as wages subject to income tax withholding, Social Security, and Medicare.⁴ Code L on your W-2 is the non-taxable piece; if you see nothing in Box 12 and know you received per diem, that’s a warning sign.

Payments made under a fully compliant accountable plan and within federal rates don’t appear in Box 1 at all, aren’t subject to withholding, and aren’t hit with Social Security or Medicare tax.² For tax purposes, the payment effectively never happened.

When the Plan Fails

If any of the three accountable plan requirements is missing, the arrangement is treated as non-accountable. The entire per diem is reclassified as wages. The full amount lands in Box 1, income tax withholding applies, and the employee owes their share of Social Security and Medicare on money they actually spent on hotels and meals.⁵

And because unreimbursed employee business expenses are no longer deductible, there’s no way to claw any of that back on your return. The narrow exceptions cover armed forces reservists, qualified performing artists, fee-basis state or local government officials, and K-12 educators (who can deduct up to $300 in qualified expenses). Everyone else pays tax on the full amount with no offset. If you’re routinely receiving per diem, it’s worth confirming with payroll or HR that the plan is set up as accountable.

The Federal Rates That Set the Ceiling

The federal rate is what determines how much per diem can flow tax-free. There are two components: lodging and Meals and Incidental Expenses (M&IE). Incidental expenses cover tips for baggage handlers, porters, and hotel staff, along with laundry and dry cleaning during the trip. They don’t cover phone calls, transportation between hotel and restaurants, or lodging taxes.⁵

Employers can use location-specific rates published by the General Services Administration. For fiscal year 2026 (October 2025 through September 2026), the standard CONUS rate is $110 for lodging and $68 for M&IE, with high-cost cities running well above that.⁶

Tracking every city rate is a lot of overhead, so the IRS also allows a High-Low Substantiation Method that sorts every CONUS destination into one of two buckets. For the period beginning October 1, 2025, the high-cost rate is $319 per day and the low-cost rate is $225.⁷ Of the $319, $86 is the meal portion; of the $225, $74 is the meal portion.

First and last days of a trip are prorated. Federal rules pay 75% of the applicable M&IE rate on departure day and on the final day of travel, with 100% for full days in between.⁸

Self-Employed Travelers

Self-employed taxpayers can use per diem, but only for meals. Lodging has to be tracked and deducted at actual cost.⁹ The meal per diem is subject to the same 50% limitation employers face, so you deduct half the applicable M&IE rate for each travel day. The deductions go on Schedule C, or Schedule F for farmers.¹⁰ Because business travel is a direct business expense rather than an employee reimbursement, the TCJA elimination of miscellaneous itemized deductions never touched it. You still need to document dates, locations, and business purpose for every trip.

Transportation Industry Workers

Truck drivers, airline crew, railroad workers, and others subject to Department of Transportation hours-of-service limits get two breaks. The M&IE rate is flat regardless of location: $80 per day within the continental United States and $86 outside CONUS.⁷ More importantly, the meal deduction percentage is 80% instead of the standard 50%. IRC Section 274(n)(3) provides that enhanced rate for food and beverages consumed while away from home during a period of duty subject to federal hours-of-service limitations.¹¹ Thirty extra percentage points add up quickly for someone on the road most of the year.

1
Internal Revenue Service. Publication 529 (12/2020), Miscellaneous Deductions
2
Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses
3
eCFR. 26 CFR 1.62-2 – Reimbursements and Other Expense Allowance Arrangements
4
IRS. 2026 General Instructions for Forms W-2 and W-3
5
IRS.gov. Per Diem Payments Frequently Asked Questions
6
GSA. GSA Releases FY 2026 CONUS Per Diem Rates for Federal Travelers
7
IRS. 2025-2026 Special Per Diem Rates, Notice 2025-54
8
eCFR. Part 301-11 Subsistence Expenses
9
IRS. Per Diem Rates – Topical Index
10
Internal Revenue Service. Topic No. 511, Business Travel Expenses
11
Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses