A per diem is a flat daily amount an organization pays someone for the cost of business travel, instead of reimbursing what was actually spent. Per diem is a Latin phrase that translates to per day, and the payment is generally calculated on a set rate rather than on actual expenses incurred (Cornell Legal Information Institute, per diem). For tax, the point of paying that way is that a per diem within limits proves the amount of the expense without receipts for it.
What the Allowance Covers
The federal travel rules give the fullest definition, and they are the source of the rates almost everyone else borrows. The per diem allowance, also referred to as subsistence allowance, is a daily payment instead of reimbursement for actual expenses for lodging, excluding taxes, meals, and related incidental expenses, and it is separate from transportation expenses and other miscellaneous expenses (41 CFR 300-3.1).
The same definition sets out three components. Lodging takes in expenses, except lodging taxes in the United States, for overnight sleeping facilities, baths, personal use of the room during daytime, telephone access fees and service charges for fans, air conditioners, heaters and fires furnished in the room where those charges are not included in the room rate. Meals takes in breakfast, lunch, dinner and related tips and taxes, and specifically excludes alcoholic beverage and entertainment expenses and any expenses incurred for other persons. Incidental expenses means fees and tips given to porters, baggage carriers, hotel staff and staff on ships (41 CFR 300-3.1).
Lodging tax splits by geography, and it catches people out. Lodging taxes in the United States are excluded from the per diem allowance and are reimbursed as a miscellaneous expense, while in foreign locations lodging taxes are part of the per diem allowance and are not a miscellaneous expense (41 CFR 300-3.1).
Where the Federal Rate Comes From
The rate has a definition of its own, and it is a ceiling rather than an average. The regular federal per diem rate is the highest amount that the federal government will pay to its employees for lodging and meals and incidental expenses, or meals and incidental expenses only, while they are traveling away from home in a particular area, and the rates are different for different localities (IRS, Publication 463 (2025)).
The rates run on the government’s year, not the calendar. Per diem rates are listed by the federal government’s fiscal year, which runs from October 1 to September 30 (IRS, Publication 463 (2025)). The publication puts the choice in the taxpayer’s hands and then closes it: rates from the 2024 fiscal year per diem tables or from the 2025 fiscal year tables may be used, but the same tables must be used consistently for all travel reported on the income tax return for the year (IRS, Publication 463, for use in preparing 2025 returns).
The Standard Meal Allowance
Where lodging is handled some other way, the meals side has its own name. The standard meal allowance is the federal rate for meals and incidental expenses, and it can generally be used as an alternative to the actual cost method, letting a set amount stand in for daily meals and incidental expenses instead of records of actual costs (IRS, Publication 463 (2025)). For travel in 2025, the rate for most small localities in the United States is $68 per day, and most major cities and many other localities qualify for higher rates (IRS, Publication 463 (2025)).
Using it does not switch the records off. Anyone using the standard meal allowance must still keep records to prove the time, place and business purpose of the travel (IRS, Publication 463 (2025)). There is also a narrower optional method for deducting incidental expenses only, where the amount of the deduction is $5 a day, available only if no meal expenses were paid or incurred, unavailable on any day the standard meal allowance is used, and subject to the proration rules for partial days (IRS, Publication 463 (2025)).
What Makes a Per Diem Count as Adequate Accounting
This is the part that decides whether the payment is a reimbursement or pay. A per diem or car allowance satisfies the adequate accounting requirements for the amount of the expenses only if all of four conditions apply: the employer reasonably limits payments of the expenses to those that are ordinary and necessary in the conduct of the trade or business; the allowance is similar in form to and not more than the federal rate; the employee proves the time, meaning dates, the place and the business purpose of the expenses to the employer within a reasonable period of time; and the employee is not related to the employer (IRS, Publication 463 (2025)).
Every one of the four has to hold. The third is the one that fails in practice, because a flat payment made with no dates, place or purpose recorded against it has proved nothing, however correct the rate was.
At the Federal Rate, and Above It
The reporting follows the comparison. If the allowance is less than or equal to the federal rate, the allowance is not included in box 1 of Form W-2, and the recipient need not report the related expenses or the allowance where the expenses are equal to or less than the allowance (IRS, Publication 463 (2025)).
Above the rate it splits in two. If the allowance is more than the federal rate, the employer must include the allowance amount up to the federal rate under code L in box 12 of Form W-2, that amount is not taxable, and the excess allowance is included in box 1 and reported as if it were wage income (IRS, Publication 463 (2025)). So an over-rate per diem does not void the whole payment. Only the excess becomes wages.
Per annum covers the other Latin rate tag that turns up in the same files, and the same trap sits under both, which is that the tag names a period and settles nothing else.
A firm that wants travel reimbursement files checked against these rules by someone else can hand Accountably a block of its own work through a trial task and grade it before anything live depends on it.
