How Do I Prove My Mileage to the IRS?

You prove your mileage to the IRS with a contemporaneous log: a record, created close to when you drove, showing the date, the start and end of each trip, the business purpose, and the miles driven. A bank statement or a number you estimated at tax time isn't enough. Mileage is held to a strict substantiation standard, so the quality of your log is what stands between you and your deduction in an audit.

The Four Things Every Trip Record Must Show

For each business trip, the IRS expects:

• Date of the trip
• Starting location and destination
• Business purpose of the drive
• Miles driven

You also need your total miles for the year, because the deduction is based on the business-use share of your driving. Traditionally that meant odometer readings at the start and end of the year, but an always-on tracker that logs every trip gives you the same total automatically.

What "Contemporaneous" Really Means

"Contemporaneous" is the word that trips people up. It means your log is created at or near the time of each trip, not reconstructed from memory in April. A calendar full of guesses, or a spreadsheet filled in the night before filing, is exactly the kind of record auditors discount.

This is stricter than it is for many other expenses. Vehicle mileage is "listed property" under the tax code, which means the IRS can, and routinely does, disallow deductions backed only by estimates. There's no "close enough" allowance for miles the way there sometimes is for other costs. If you can't substantiate it, you generally can't claim it.

What Happens If You're Audited

In a mileage audit, the IRS asks for your log and tests whether it's credible. They look for:

• Records that line up with your calendar, income, and the type of work you do
• Consistent, timely entries rather than round numbers added in bulk
• Reasonable total mileage for the business you run

Handwritten logbooks and memory-based reconstructions fail here more often than people expect. A digital log with timestamps, real start and end addresses, and the actual route driven is far harder to dispute, because it was clearly recorded as you drove.

Why an Automatic Log Holds Up Better

This is where automatic tracking earns its keep. Every field the IRS wants maps directly to what a tracker records as you drive:

• Date, captured automatically the moment a trip is detected
• Start and end address, GPS coordinates reverse-geocoded to real street addresses
• Business purpose, classified per trip, so the "why" is attached to every drive
• Miles driven, accurate, road-snapped distance, not a straight-line estimate
• Yearly total, a running total across every trip, ready for your return

Because the record is built in real time, it's contemporaneous by definition. For more on the rate those miles are worth, see the 2026 IRS mileage rate, and to estimate your own deduction, try our 1099 tax calculator.

Start Building an Audit-Ready Log Today

The best time to fix your mileage records is before you need them. Smart Miles tracks every drive automatically, attaches a real route and address to each one, and exports a clean log your accountant, or an auditor, can read at a glance. If you drive for work as a contractor or freelancer, that complete record is the difference between claiming your full deduction and defending a number you can't back up. See how automatic tracking works and start your log today.