IRS Mileage Log Requirements: The Exact Format Auditors Want
A vague mileage log is the fastest way to lose your vehicle deduction in an audit. Here's exactly what the IRS requires on every entry — and the sample format that holds up.
The vehicle deduction is one of the largest write-offs available to self-employed people and small business owners — and one of the most frequently denied in an audit. The reason is almost always the same: the mileage log doesn't meet the IRS's documentation standard. The deduction itself is legitimate; the record isn't.
This guide lays out precisely what the IRS expects, the fields every entry must contain, what a compliant sample looks like, and the mistakes that get deductions thrown out.
For each business trip: the date, the business purpose, the start and end point, and the miles driven. Plus your total annual mileage and a way to separate business from personal use. Records should be contemporaneous — written down at or near the time of the trip.
The four fields every entry must have
IRS Publication 463 governs vehicle expense records. Boiled down, each line of your log needs four things:
- Date of the trip — the actual calendar date you drove.
- Business purpose — why you drove. "Client meeting — Acme Corp" works; "business" alone does not.
- Destination / route — where you went, ideally start and end location so the distance is verifiable.
- Miles driven — the business miles for that trip.
Miss any one of these consistently and the log is considered inadequate, even if your mileage is genuine.
A compliant sample mileage log
Here's what a single week looks like in an audit-ready format:
| Date | Purpose | From → To | Miles |
|---|---|---|---|
| Mar 3 | Client meeting — Acme Corp | Office → 14 King St | 18.4 |
| Mar 4 | Supplier pickup | Office → Warehouse District | 9.1 |
| Mar 6 | Site visit — Johnson job | Home → 220 Pine Ave | 31.7 |
| Mar 7 | Bank + post office (business) | Office → Downtown → Office | 6.5 |
Notice every row answers all four questions. An auditor can take any line and verify the distance on a map. That's the bar.
Standard mileage rate vs actual expenses
There are two ways to claim vehicle costs, and your log supports both:
- Standard mileage rate — multiply your business miles by the IRS rate for the year (70¢/mile in 2025; confirm the 2026 figure with the IRS each January). Simplest, and the log is your documentation.
- Actual expense method — deduct the business-use percentage of gas, insurance, repairs, depreciation, etc. Here your log establishes the business-use percentage (business miles ÷ total miles).
Either way you need total annual mileage, which is why recording your odometer at the start and end of the year matters.
Contemporaneous vs reconstructed logs
The single most important word in IRS vehicle rules is contemporaneous — meaning you recorded the trip at or near the time it happened. A log built in real time is far stronger evidence than one assembled the night before an audit.
Can you reconstruct a log after the fact? Sometimes — using calendar entries, appointment history, and map distances. But reconstructed logs are routinely challenged and partially disallowed. If you've fallen behind, rebuild from the most reliable records you have, and start logging contemporaneously going forward.
Generate an IRS-compliant mileage log free
Every required field, the current standard rate baked in, and a clean PDF you can hand to your accountant or an auditor. Templates for self-employed, Uber, DoorDash and real estate.
The five mistakes that kill a mileage deduction
- "Business" as the purpose — too vague. Name the client, errand, or job.
- Round numbers everywhere — a log full of "20, 20, 20, 50" looks estimated. Real trips have odd distances.
- No total annual mileage — without it the IRS can't verify your business-use percentage.
- Commuting claimed as business — driving from home to your regular workplace is personal, not deductible.
- Gaps and backfilling — a log that's clearly written all in one sitting (same pen, same day) undermines the contemporaneous standard.
How long to keep your mileage records
Keep mileage logs and supporting records for at least three years from the date you filed the return, which is the general IRS audit window. If you under-reported income substantially the window extends to six years, so many accountants suggest keeping vehicle records for that long to be safe.