The IRS standard mileage deduction is simple in concept — multiply your business miles by the current rate — and the part people actually get wrong isn't the math. It's the record you're supposed to have before you ever claim the deduction. Here's what IRS Publication 463 actually requires, not what a vague "keep good records" reminder implies.

Source: IRS Publication 463, Travel, Gift, and Car Expenses. Verified October 3, 2026. This article is general information, not tax advice — talk to your accountant about your specific situation.

The 4 things every trip's record needs

Per Publication 463, each business trip needs:

Date of the trip.
Destination — where you went.
Business purpose — why the trip was for business, not just that it happened to be in a work vehicle.
Miles driven for that trip.

On top of the per-trip log, the IRS also expects odometer readings at the start and end of the tax year — the total-mileage bookends that your business-mile log should fit inside.

"Contemporaneous" doesn't mean instant — it means not reconstructed later

Records have to be kept at or near the time of each trip, not pieced together from memory when you file in April. Publication 463 is explicit that a weekly log counts as timely — you don't need to log every single trip the moment it ends, but you shouldn't be rebuilding a year of travel from a blank page either. The practical takeaway: a log you update as you go beats a perfect-looking spreadsheet you built in one sitting months later, because the IRS can tell the difference in an audit and the second one is far more likely to get your deduction disallowed.

What "adequate records" actually means

Adequate records are whatever combination of a log, diary, or trip record — plus receipts or statements where relevant — that together prove the date, place, business purpose, and amount of each expense. The IRS does allow sampling methods for high-volume situations, and there are narrow exceptions if records were genuinely destroyed (fire, theft, and similar), but neither of those is a substitute for keeping a real log in the first place.

What happens if your records fall short

If you can't substantiate a deduction, the IRS can disallow it — not reduce it, disallow it entirely for the trips that aren't backed up. This is the actual cost of a vague log: it's not a smaller deduction, it's none.

One rule that trips people up: you can't mix deduction methods

You have to choose the standard mileage rate or the actual-expense method (gas, maintenance, depreciation, insurance, etc.) for a given vehicle in a given year — not both. If you want the option to use the standard mileage rate, the standard advice is to use it the first year the vehicle is placed in service for your business, since switching methods later has its own restrictions.

How automatic trip logging fits into this

Everything above describes what a manual mileage log needs to contain. A GPS-based system satisfies the same requirements differently: every trip is recorded automatically — date, start and end location (geocoded to an address), and distance — the moment it happens, which is about as "contemporaneous" as a record can get. The one thing a GPS device genuinely cannot know on its own is why the trip happened — business purpose is a judgment call only a person can make, which is why trip classification (tagging a trip as business or personal) is still a step you or a driver does, not something the hardware infers.

See how GPS fleet tracking works for how trips get built from raw position data in the first place, and our 2026 mileage rate guide for the exact rate to apply to whatever your log adds up to this year.

Business vs. Personal Mileage: How to Keep an IRS-Ready Log