The IRS mileage log requirements come from Section 274(d) of the Internal Revenue Code, and they are specific: for every business trip, you have to record the date, the destination, the business purpose, and the miles driven, plus your vehicle’s odometer reading at the start and end of the tax year.1Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses Vehicle expenses get no fallback estimation rule. If the log is missing or incomplete, the IRS can deny the entire deduction.
The Four Elements Every Trip Entry Needs
IRS Publication 463 spells out what each log entry has to capture, and the elements map directly to the statutory language in Section 274(d).2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses
- Date. The specific day you used the vehicle for business. A log that lumps multiple days together or records only weekly totals won’t hold up.
- Destination. Where you drove. A client name, office address, or jobsite location is enough. “Downtown” is not.
- Business purpose. Why the trip was necessary. “Met with client to review contract” works. “Business meeting” is too vague.
- Miles. The number of miles driven for that business segment. It needs to match the route between the locations you recorded.
One shortcut the rules do allow: several stops that are part of one continuous business trip can be combined into a single entry. A round trip to a client’s office, or a route with several business stops and a quick lunch break between them, counts as one use.
Odometer Readings
Separate from trip entries, you record your odometer at the beginning and end of each tax year. The IRS uses those two numbers to derive your business-use percentage — total business miles divided by total miles for the year. That percentage matters directly under the actual expense method and works as a plausibility check under the standard mileage rate.2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses If your business miles imply a total-mile figure that doesn’t fit your vehicle’s actual usage, that gap is the first thing an auditor will notice.
When to Record: The Contemporaneous Rule
Publication 463 expects entries to be made at or near the time of each trip, and it emphasizes that written records carry more weight than oral statements.2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses There is no bright-line rule like “within 24 hours,” but the practical standard is same-day or next-day. A log reconstructed weeks or months later is exactly the kind of evidence auditors challenge, and the longer you wait, the less specific you can be about purpose and destination.
Which Trips Belong in the Log
Only driving that’s ordinary and necessary for your trade or business goes in. Driving to a client’s office, between two worksites, or to a temporary job location qualifies. Picking up supplies for a project qualifies.
Commuting does not. The drive from home to your regular workplace and back is personal mileage no matter how far it is. The main exception is when your home qualifies as your principal place of business (you have a dedicated home office); in that case, trips from home to temporary work locations or client sites become deductible business travel rather than commuting.3Internal Revenue Service. Topic No. 510, Business Use of Car
Personal driving — errands, social trips, vacations — must stay out of your business total. You don’t have to log every personal trip in detail, but your odometer readings need to account for the difference between business miles and total miles. If you drove 18,000 miles for the year and claim 15,000 as business, the remaining 3,000 personal miles have to be plausible for your situation.
Acceptable Formats
The IRS doesn’t mandate any particular format. Paper notebooks, spreadsheets, and smartphone apps all work, as long as the result captures the four elements and entries are made close to when the trips happen.
Paper Logs
A simple notebook or printed template is fine. Nothing to sync, nothing to crash, and handwritten dates carry their own credibility. The downside is that paper logs are easy to neglect. A week of missed entries can snowball into a month of estimates, which is exactly the reconstruction problem the IRS pushes back on.
GPS Apps and Telematics
GPS-enabled apps and vehicle telematics can record trips automatically, capturing date, route, and mileage without manual input. The reports they generate satisfy the requirements as long as the output includes all four elements. Since GPS alone can’t tell why you were driving, most apps prompt you to classify each trip and add a business purpose. Electronic records need to be backed up and exportable in a readable format.
The Sampling Method
If you drive a regular, repeating route — visiting the same clients on a fixed schedule, for example — the IRS lets you log a representative sample period and extrapolate across the full year. You have to be able to show the sample reflects your typical driving, and if your route changes mid-year, the sample has to be updated. This is most useful for delivery drivers or service professionals with predictable weekly circuits.
What Happens If Your Log Is Missing or Weak
Vehicle expenses occupy an unusually strict corner of tax law. For most deductions, if your records are imperfect, a court can allow a reasonable estimate under what’s known as the Cohan rule. Section 274(d) was enacted specifically to override that safety net for vehicle expenses, travel, and gifts.4Internal Revenue Service. The Cohan Rule – An IRS Audit Defense Tool No adequate log means no deduction, not a reduced one.
When vehicle deductions are disallowed, the underpayment can trigger a 20% accuracy-related penalty on top of the additional tax.5Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments The statute defines negligence to include any failure to make a reasonable attempt to comply with tax rules, and failing to keep adequate records is a textbook example. Interest accrues from the original due date of the return, so the longer the gap between filing and audit, the larger the bill.
A taxpayer who acted in good faith with reasonable cause can potentially avoid the penalty, but “I didn’t know I needed a log” is a hard argument when the requirement is printed in every set of Schedule C instructions.
How Long to Keep the Log
The general rule is three years from the date you filed the return, or from the return’s due date, whichever is later. Returns filed early are treated as filed on the due date, so a 2026 return filed in February 2027 starts its three-year clock on April 15, 2027.6Internal Revenue Service. Topic No. 305, Recordkeeping
If you’re depreciating your vehicle under the actual expense method, keep the logs and related records until three years after the year you stop claiming depreciation, whether because the vehicle is fully depreciated, sold, or taken out of service. Passenger automobile depreciation can stretch five or more years, so first-year records often need to survive eight years or longer.7Internal Revenue Service. How Long Should I Keep Records
If you underreport income by more than 25%, the IRS has six years to assess additional tax, and your records need to survive that longer window.
Non-Business Mileage Follows the Same Rules
The same substantiation standards apply if you drive for medical care, for a qualified charity, or, for active-duty Armed Forces members and certain intelligence community members starting in 2026, for a qualifying move.8Internal Revenue Service. Topic No. 455, Moving Expenses for Members of the Armed Forces and the Intelligence Community Each trip still needs the date, destination, purpose, and miles. For charitable driving, if the value of your donated driving plus any other contributions to the same organization totals $250 or more, you also need a written acknowledgment from the charity in addition to your log.9Internal Revenue Service. Charitable Contributions: Written Acknowledgments
The log itself doesn’t get submitted with your return. You keep it in your records and produce it if the IRS asks.