Expense Report Audit Checklist: Substantiation, Plan, and Review

An expense report audit checklist works through five gates in order: IRS substantiation, accountable plan compliance, internal policy limits, correct tax classification, and screens for duplicates or personal charges. Clearing all five — and keeping the paperwork to prove it — is what protects the company’s deductions and keeps reimbursements tax-free to employees. The items below are what to check on every report you pull for review.

Substantiation: The Four Elements and the $75 Rule

Section 274(d) of the Internal Revenue Code sets the federal floor. For travel, gifts, and listed property, no deduction is allowed unless the taxpayer can substantiate four things: the amount, the time and place, the business purpose, and the business relationship of anyone else who benefited from the spending.¹ Courts have consistently given more weight to records created at or near the time of the expense than to logs reconstructed weeks later, so treat after-the-fact summaries as a red flag.²

The receipt threshold comes from Treasury Regulation 1.274-5(c)(2)(iii): documentary evidence is required for any lodging expense and for any other expense of $75 or more, with a carve-out for transportation charges where a receipt isn’t readily available.³ Non-lodging expenses under $75 don’t need a receipt under federal rules, though many companies set a lower internal threshold — sometimes $25 — to catch errors earlier.⁴

What a receipt has to show:

Merchant name and location
Date of the purchase
Itemized description of what was bought
For restaurants, the number of people served
For hotels, separate line items for lodging, meals, and incidentals

Cross-check the receipts against credit card statements or bank records so the amounts line up. Rounded figures with no receipt — “$200 for client dinner” — fail the standard. When documentation is incomplete, the employee has to provide a written statement with specific details plus corroborating evidence, and at that point the deduction is on shaky ground.

Accountable Plan Compliance

This is the single most consequential check on the list, because it determines whether reimbursements are tax-free to the employee or taxable wages. An accountable plan has to satisfy three conditions:

Business connection — the expense relates to services the employee performed for the employer.
Adequate accounting — the employee submits documentation within a reasonable time.
Return of excess — advances exceeding actual expenses are returned, generally within 120 days.

These come from IRS Publication 463 and mirror Section 62(c) of the Code, which makes clear that an arrangement fails if it skips substantiation or lets employees keep unspent advances.⁴⁵

When a plan fails any of the three tests, every reimbursement under it becomes a nonaccountable payment. The consequences hit immediately: amounts become taxable wages, get reported on the W-2, and are subject to income tax withholding and employment taxes.⁶ So verify two things on each report: substantiation arrived on time, and any excess advance was returned. Attached receipts alone aren’t enough.

Policy Limits and Rate Checks

Mileage

The 2026 IRS standard mileage rate for business use of a personal vehicle is 72.5 cents per mile, effective January 1.⁷ Reimbursement at or below this rate is tax-free under an accountable plan; anything above it is taxable income to the employee. Verify mileage logs against mapping tools and confirm the current year’s rate was used. Payments calculated at a prior year’s rate are a routine error.

Per Diem

For domestic travel under a per diem system, match the figures to the GSA tables. The FY2026 standard CONUS rate is $110 per night for lodging and $68 for meals and incidental expenses, with roughly 300 designated high-cost areas at higher allowances.⁸ International travel uses State Department rates by country and city.⁹ Confirm the correct locality rate was applied. Employees sometimes pull the rate for the nearest high-cost city rather than the one where they actually stayed.

Pre-Authorization

For expenses above the policy’s approval threshold or for premium bookings like first-class airfare, check that written approval predates the expense. Retroactive sign-off after the charge already hit defeats the point of the control.

Tax Classification: Watch for Entertainment

Coding errors that look clerical can directly reduce the company’s deductions. The Tax Cuts and Jobs Act made entertainment expenses entirely nondeductible starting in 2018.¹⁰ Employees may code concert tickets, sporting events, golf outings, or similar activities as “meals” or “client development,” but federal law disallows deductions for any activity generally considered entertainment, amusement, or recreation — regardless of whether a business discussion took place during the event. Club dues get their own prohibition: no deduction is allowed for dues paid to any club organized for business, pleasure, recreation, or social purposes.¹

Isolating these charges is where the audit adds real value. Entertainment lumped into travel or meals means the company overclaims on its tax return, and if the IRS catches the error later, the business loses the deduction and can face a 20% accuracy-related penalty on the resulting underpayment.¹¹

Spousal and Family Travel

Travel costs for a spouse or family member accompanying an employee are disallowed unless all three conditions are met: the spouse is also an employee, the travel serves a genuine business purpose, and the expenses would be independently deductible by the spouse.¹ “My spouse came to the conference” doesn’t qualify. If the employer pays anyway, it can treat the cost as additional compensation — deductible by the employer, taxable to the employee.¹² Flag any report that includes charges for a non-employee companion so accounting can handle the tax treatment.

Duplicates, Personal Charges, and Missing Purpose

Most audit findings aren’t sophisticated fraud. They’re the same receipt on two reports, a personal charge buried in a hotel folio, or two employees each claiming the full tab for the same dinner. Screen for these patterns on every report:

Duplicate submissions — the same receipt on multiple reports, or the same charge submitted by different employees. Matching by date, merchant, and amount catches most.
Personal charges in hotel folios — room service, minibar, in-room movies, spa. Strip these out before reimbursement.
Tips wildly out of proportion to the underlying meal total.
Missing business purpose. Every deductible expense must be both ordinary and necessary for the business — common in the industry and helpful for operations. Reports should document who attended a business meal and why.¹³

How to Run the Review

Few organizations audit every report. Most sample. Statistical sampling selects reports randomly and projects findings with quantifiable confidence; nonstatistical sampling uses professional judgment to target high-risk submissions — large dollar amounts, frequent travelers, new employees. Both are accepted under professional auditing standards.¹⁴ A common hybrid is random selection of a baseline percentage plus mandatory review of anything above a dollar threshold.

Each report ends up in one of three buckets: approved for payment, rejected for a policy violation, or held for more information. When something’s wrong, tell the employee exactly what’s missing. Vague rejection notices slow reimbursement and frustrate people who could resolve the issue in five minutes with clear direction. Once cleared, the report moves to payroll or accounts payable. Keep a documented trail throughout: who reviewed, what was flagged, how it was resolved, when payment was authorized. That trail is what protects the company if an external audit follows.

Record Retention

The IRS generally requires businesses to keep records supporting expense deductions for at least three years from the date the return was filed.¹⁵ Employment tax records — relevant whenever reimbursements affect wage calculations — should be kept four years.¹⁶ The clock starts from the filing date or the tax payment date, whichever is later. Underreporting income by more than 25% extends the window to six years, and there is no statute of limitations on fraudulent returns. Most organizations keep expense documentation for at least seven years to cover extended audit scenarios. Digital storage handles the volume; the real work is organizing files so a specific report can actually be retrieved three years out.

What Happens When Findings Come Back

If the IRS disallows expense deductions on examination, the company owes tax on the income that should not have been offset. The agency can add a 20% accuracy-related penalty when the underpayment stems from negligence or a substantial understatement, plus interest running from the original due date.¹¹ A company whose plan turns out to be nonaccountable faces retroactive employment tax liability on every reimbursement paid under it, plus the work of correcting W-2s. Catching these issues internally — before an external examiner does — is the whole reason the checklist exists.

1
Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses
2
The Tax Adviser. Substantiating Expenses: All or Nothing
3
eCFR. 26 CFR 1.274-5 – Substantiation Requirements
4
Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses
5
Office of the Law Revision Counsel. 26 USC 62 – Adjusted Gross Income Defined
6
Internal Revenue Service. Revenue Ruling 2003-106
7
Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate at 72.5 Cents per Mile, Up 2.5 Cents
8
GSA. Per Diem Rates
9
U.S. Department of State. Office of Allowances – Per Diem Rates
10
Internal Revenue Service. Tax Cuts and Jobs Act: A Comparison for Businesses
11
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
12
Internal Revenue Service. Spousal Travel
13
Internal Revenue Service. Ordinary and Necessary
14
Public Company Accounting Oversight Board. Audit Sampling
15
Internal Revenue Service. How Long Should I Keep Records
16
Internal Revenue Service. Taking Care of Business: Recordkeeping for Small Businesses