Surviving a Mileage Audit: What to Do When the IRS Asks

Mileage deductions are one of the most-questioned items in IRS audits because they are easy to estimate and hard to verify without a clean log. If you get audited, here is how to handle it.

What the IRS will ask for

In a correspondence audit (the most common type), the IRS sends a letter listing the items they want documentation for. For mileage, they typically request:

• Your mileage log for the year. Date, destination, business purpose, miles for each trip
• Odometer readings at the start and end of the year
• Vehicle make, model, year, date placed in service
• Documentation of business activity (1099s, customer invoices, gig platform statements) consistent with the claimed business miles

Step 1: Do not panic, do not improvise

Do not call the auditor and improvise answers on the phone. Read the audit letter carefully. The letter will list exactly what they need and a deadline (usually 30 days, sometimes longer). If you need more time, you can request an extension in writing.

Step 2: Send the documentation, not commentary

Mail or upload exactly what was requested. A clean log + supporting evidence + a brief cover letter listing what you are submitting. Do not write paragraphs explaining or arguing. That triggers more questions. The documentation should speak for itself.

Step 3: If your log is incomplete, be honest

Inflated reconstructed numbers are worse than admitting partial documentation. If you tracked half the year and are reconstructing the other half from calendar and gas receipts, say so plainly with a methodology note. See how to reconstruct properly.

What holds up

• Contemporaneous logs from a tracking app, dated entries spread evenly across the year, totals matching odometer readings.
• Plausible business-use percentage given the vehicle's total mileage and the nature of the work.
• Round-trip distances that match map estimates between the documented destinations.
• Underlying business activity (1099 income, customer invoices, gig platform statements) that scales with the claimed miles.

What loses deductions

• Round numbers (exactly 20,000 business miles).
• 100% business use on a single personal vehicle (almost no one has zero personal driving).
• Year-end reconstruction with no contemporaneous evidence.
• Missing fields. "Date and destination but no business purpose" gets that trip disallowed in many audits.
• Mileage claimed on days no other business activity is documented.

Step 4: If they propose a change, decide whether to fight

After reviewing your documentation, the IRS may issue a "30-day letter" proposing to disallow some or all of your deduction. You have three choices: agree and pay the additional tax, request an appeals conference, or take it to Tax Court. For mileage cases under $50,000, Tax Court has a small-case procedure that is more accessible than full Tax Court litigation.

When to hire a tax pro

For a correspondence audit on a single year with under $10,000 in disputed mileage and a clean log, most filers can handle the response themselves. For office or field audits, multi-year disputes, or claims over $25,000, an enrolled agent or tax attorney is worth the cost. The IRS treats represented taxpayers measurably better.

How to stop worrying about audits

Audit risk drops dramatically when your mileage log is contemporaneous, your numbers are plausible against your stated business, and your supporting evidence (1099s, invoices, gas receipts) lines up with claimed miles. Auto-tracking apps generate contemporaneous logs by default. The trip is timestamped at the moment it happens.

Audit-defensible by construction. Start free with TruMile →