What the IRS Requires in a Mileage Log (2026)

The IRS requires four pieces of information for every business mile you claim. Date of the trip, destination, business purpose, and miles driven. That is it. Anything beyond that is optional. Anything missing is a problem in an audit.

Source: IRS Publication 463, Travel, Gift, and Car Expenses

The Four Required Fields

Every entry in your mileage log must show:

• Date. The day the trip happened. Not the week, not the month. The specific date.
• Destination. Where you went. A street address, a client name, or a job-site identifier is enough. "Downtown" is not.
• Business purpose. Why the trip was for work. "Meeting with client Smith," "job site 4031 Maple," "supply pickup at Home Depot." One short phrase is fine.
• Miles. The actual distance driven. Round-trip is fine if that is what you drove.

A column for starting odometer reading is helpful but not required by the IRS. Total annual mileage IS required (start and end of year), so most drivers note odometer readings on January 1 and December 31.

The Contemporaneous Rule

The IRS calls a mileage log contemporaneous if it is created at or near the time of the trip. Reconstructing your year from memory in March before filing is the opposite of contemporaneous.

Contemporaneous logs hold up. Reconstructed logs get challenged. The Tax Court has ruled against drivers in dozens of cases where the only mileage record was a year-end reconstruction, even when the underlying business activity was real.

A note logged the day of the trip is contemporaneous. A note logged within a week of the trip is generally accepted as contemporaneous. A spreadsheet built in March from memory and old calendar entries is not.

Three Acceptable Log Formats

The IRS does not require a specific format. Any of these work, as long as the four required fields are present and the log is contemporaneous:

• Paper logbook. A spiral notebook in your glove box with one row per trip. Cheapest. Easiest to lose.
• Spreadsheet. Excel or Google Sheets. Faster than paper. Still requires you to enter every trip yourself, which is the failure point for most people.
• Mileage tracking app. An app that auto-detects trips and timestamps them at the moment they happen. Contemporaneous by construction. More on this in the tracking guide.

How Long to Keep Records

The IRS can audit your taxes for three years from the filing date in normal circumstances, six years if you understated income by more than 25 percent, and indefinitely if there is fraud. Most tax professionals advise keeping mileage records for at least seven years.

What Happens in an Audit

The IRS will ask to see your log. They will look for the four required fields. They will look at trip frequency for plausibility. If you claimed 30,000 miles but your log only documents 8,000, the difference gets disallowed. If your log is reconstructed and obviously so, the entire deduction can be disallowed.

A clean log with the four fields, dated entries spread evenly across the year, and a plausible total against your stated business activity is what holds up. The IRS is not trying to trick you. They are checking whether the deduction matches a real pattern of business driving.

FAQ

Do I need to log personal miles too?

Only if you are using the actual-expense method, in which case you need total annual miles to calculate the business-use percentage. Under the standard mileage rate, you only need to log business miles plus your January 1 and December 31 odometer readings.

Does the IRS accept app-based mileage logs?

Yes. The IRS does not specify a format. An app-generated log is acceptable as long as the four required fields are present and the data is contemporaneous. Most apps export to PDF or CSV for tax filing.

Can I use Google Maps Timeline as my mileage log?

Not by itself. Google Maps Timeline records location history but does not flag trips as business or personal, and it does not record business purpose. You would need to manually annotate every business trip with purpose, which defeats most of the time savings. A purpose-built mileage app is more practical.

What if I forgot to log a trip?

Add it as soon as you remember, with the actual date. A back-fill within a few days is generally fine. A back-fill from months ago is reconstructed and weakens the contemporaneous defense for that entry. Going forward, the goal is to never have gaps.

Is a bank statement enough proof?

No. A bank statement shows you bought gas. It does not show where you drove or why. The mileage log is the primary record. Bank and credit-card statements are corroborating evidence at best.

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