The standard mileage deduction is simple to claim — until the IRS asks for your records. At that point, “I drove a lot for work” is not a defensible answer.

The IRS has clear requirements for mileage documentation. Here’s what your log needs to include, what format it can take, and what to do if your records aren’t where they should be.

The Legal Basis

The IRS requires what it calls adequate records to substantiate vehicle expense deductions. This requirement comes from IRC Section 274(d), which covers listed property — a category that includes passenger automobiles.

The key phrase in IRS guidance is contemporaneous records: documentation created at or near the time of each business trip, not reconstructed later. Courts and the IRS have consistently rejected mileage logs that were clearly assembled after the fact.

What Every Mileage Log Entry Must Include

Each trip record needs to capture five elements:

1. Date — the day the trip occurred
2. Destination — where you drove to (city and general purpose location, or specific address)
3. Business purpose — a brief description of the business reason for the trip (e.g., “client meeting with Johnson Consulting,” “picked up materials for project,” “attended industry conference”)
4. Miles driven — either odometer start and end readings, or total miles for the trip
5. Starting location — especially important if you’re proving that trips originated from your home office

The business purpose is the most commonly neglected field and the most scrutinized. “Client” or “work” is not sufficient. Name the client, the project, or the business activity.

What Format Is Acceptable

The IRS does not require a specific format. Acceptable formats include:

• Paper mileage log or notebook — recorded by hand at the time of each trip
• Spreadsheet — maintained consistently with entries added per trip
• Mileage tracking app — GPS-based logs that record trips automatically
• Exported reports from accounting software — as long as the underlying data meets the five requirements above

The IRS has explicitly stated that digital records are acceptable and that you don’t need paper originals. A PDF export from a mileage app is fine.

What matters is that the records are accurate, complete, and timely — not the medium.

What the IRS Actually Checks

In an audit of vehicle deductions, an IRS examiner will typically:

1. Ask for your mileage log
2. Cross-reference logged trips against your calendar, email records, and client invoices
3. Check whether your claimed business percentage is plausible given your business type and total miles
4. Look for red flags: round numbers, entries that look templated, a log that begins suspiciously close to your audit notice

A log that shows exactly 80% business use every single week is more suspicious than one that shows 78% in January and 85% in March. Real driving patterns vary.

Odometer Records

While you don’t need to record odometer readings for every trip (total trip miles is acceptable), the IRS expects you to be able to support your total annual business miles against your total annual miles driven.

Taking an odometer photo on January 1 and December 31 each year is a good habit. If you’re ever questioned about your total business percentage, having annual odometer readings gives you an independent data point.

What About GPS Data?

GPS data from a tracking app or your phone’s location history can support your mileage log but generally isn’t sufficient on its own. The IRS still expects trip records that include the business purpose — GPS can confirm you were at a client’s address on a given day, but it can’t document why.

The best logs combine automatic GPS tracking (for accuracy and completeness) with manual business purpose annotation (for compliance). A good mileage app makes this easy.

How Far Back Do You Need to Keep Records?

The IRS generally has three years from your filing date to audit a return. However, it has six years if it suspects you understated income by more than 25%. There’s no statute of limitations for fraudulent returns.

The conservative guidance: keep mileage records for six years. Digital records are easy to store indefinitely.

What to Do If Your Records Are Incomplete

If you’re missing mileage records for part of the year, you have a few options:

Reconstruct what you can. Use your calendar, email threads, client invoices, and phone location history to identify business trips you made. Document what you can reconstruct, note that it’s reconstructed, and be conservative in your estimates. Reconstructed records are better than nothing but will receive more scrutiny.

Use corroborating evidence. If you drove to a client’s office 40 times a year, an email showing the meeting schedule, a client invoice, and a Google Maps route can support a reconstructed trip even without a contemporaneous log entry.

Consult a CPA before filing. If your records are substantially incomplete and you’re claiming a large vehicle deduction, get professional advice on how to handle it. A CPA can help you document what’s defensible.

Start fresh from today. Whatever the past looked like, begin logging every trip from here on out. A partial year of good records is better than a full year of bad ones.

The Easy Way to Always Be Compliant

The mileage log requirement sounds burdensome, but it’s genuinely simple when you have a system that captures trips automatically. You drive, the app logs it, you classify the trip in seconds. Your mileage log is always current, always IRS-ready, and you never need to reconstruct anything at year-end.

numlr logs your business drives automatically and stores every trip with the date, route, and miles needed for IRS compliance. Add a business purpose with one tap and your log is done. Try numlr free.