Updated October 29, 2026

What a mileage log needs for the IRS

For every business trip, write down the date, where you went, the business reason and the miles. Once a year, write down the car's total miles from the odometer. Do it at or near the time you drive. That's the requirement, from chapter 5 of IRS Publication 463.

For every trip

The date.
Where you went. A business name or an address is enough.
Why. “Estimate for the Ortiz kitchen” works. “Business” doesn't.
The miles. Odometer readings at the start and end are best, because they're hard to argue with.

Publication 463 also says you can't deduct amounts you approximate or estimate. A number you come up with in April for a drive last August is an estimate.

Once a year

The odometer on January 1 and on December 31, which gives you total miles for the year.
The date you started using the car for business.
What the car cost, plus any improvements. The IRS lists this for car expenses, and it matters most if you deduct actual costs instead of the standard rate.

Total miles matter because they show what share of the car's driving was business.

When to write it

The IRS wants a “timely kept” record, written at or near the time. It doesn't have to be the same day. A log you fill in once a week, covering that week, counts. A log rebuilt from memory at tax time is worth a lot less, and the IRS says so.

Paper or phone

Either works. The IRS wants a written record, and it says a record kept on a computer counts as adequate. A notebook in the glovebox is fine if you actually use it. We made a free printable mileage log if you want the columns already drawn.

Shortcuts the IRS allows

If you drive the same route over and over, like a sales or delivery route, you can record the route's length once. Then log the date of each trip and your total miles for the year.
A round trip with several business stops can be one entry. A lunch stop between two of them doesn't break it up.
You can keep a full log for part of the year, like the first week of every month, and use it for the whole year. But you have to be able to show those weeks are typical.

An example

Two trips a contractor logged on March 4:

Where and why	Odometer	Miles
Shop to 112 Elm St in Towson and back Kitchen estimate, Ortiz	18,204 to 18,227	23
Shop to Home Depot in Cockeysville Tile for the Patel job	18,227 to 18,239	12

And at the end of the year: the odometer read 15,880 on January 1 and 29,410 on December 31, so 13,530 miles in all. If 6,210 of those were business, the car was 46% business use.

How long to keep it

Generally 3 years from the date you file the return it supports. Publication 583 has the longer answer.

More mileage guides

Sources

This is general information, not tax advice. Check with a tax professional about your own return.

This is the log Milepost keeps on your iPhone. You tap Start a trip when you leave and End when you get there, and the date and odometer are already filled in. Coming soon to the App Store.