IRS mileage log requirements come from Section 274(d) of the Internal Revenue Code, which demands that every taxpayer claiming a vehicle deduction record four pieces of information for each business trip: the date, the destination, the business purpose, and the miles driven.1Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses You also need odometer readings at the start and end of the year. Entries should be made at or near the time of each trip. If the log is missing or incomplete, the IRS can deny the deduction in full.
The Four Elements Each Trip Must Capture
IRS Publication 463 translates the statute into four specific fields that every entry needs.2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses
Date. The specific day you used the vehicle for business. Weekly totals or lumped multi-day entries will not 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 to verify.
Mileage. The number of miles driven for that business segment. This figure is what feeds your deduction, and it has to be consistent with the route between the locations you recorded.
One practical allowance: multiple stops on a single continuous business trip can go into one entry. A round trip to a client with a brief lunch stop in between counts as one use, not three.
Odometer Readings and Business-Use Percentage
Beyond the per-trip entries, your records need to show your vehicle’s odometer reading at the start 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.2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses That percentage controls how much of your actual vehicle costs you can deduct, and it lets an auditor sanity-check the business miles you claim under the standard rate.
If your annual mileage and claimed business miles don’t line up with how the vehicle is actually used, the gap draws scrutiny. Driving 18,000 miles for the year and claiming 15,000 as business leaves a 3,000-mile personal total that has to be plausible for your household.
When Entries Must Be Made
Publication 463 says written records are more reliable than oral statements, and a log reconstructed weeks or months after the fact is exactly what auditors challenge.2Internal Revenue Service. Publication 463 (2025), Travel, Gift, and Car Expenses There is no bright-line deadline in the regulations, but same-day or next-day entries carry the most weight. The longer you wait, the harder it is to recall destinations and purposes with any precision, and the less credit an auditor gives the record.
The practical consequence is that a log you build at tax time from calendar entries and credit card statements is weaker evidence than one maintained throughout the year, even if the end numbers are identical.
Which Miles Count
Your log should capture miles the IRS actually allows as business driving. That means trips that are ordinary and necessary for your trade or business: driving to a client’s office, between two worksites, to a temporary job location, or to pick up supplies for a project.
Commuting does not count. The drive from home to your regular workplace and back is personal mileage, however long the commute. The main exception runs through the home office: if your home qualifies as your principal place of business, trips from there to client sites and temporary work locations are deductible business travel rather than commuting.3Internal Revenue Service. Topic No. 510, Business Use of Car
You don’t need to log every personal errand in detail, but personal driving has to be excluded from your business total, and the gap between business miles and total miles still needs to make sense against your year-end odometer reading.
Acceptable Formats for the Log
The IRS does not require any particular format. A paper notebook, a spreadsheet, or a smartphone app all satisfy the rules so long as the output captures the four required elements and the entries are made close to when the trips happen.
Paper Logs
A notebook or printed log template works. Nothing to sync, nothing to crash, and the handwritten dates have their own credibility. The weakness is neglect: a week of missed entries easily becomes a month of estimates, and estimates are the kind of reconstruction the IRS will push back on.
Electronic Tracking
GPS-enabled apps and vehicle telematics systems can record trips automatically, logging the date, route, and miles without manual input. They satisfy IRS requirements as long as the exported report includes all four elements. Because GPS alone cannot know why you drove somewhere, most apps prompt you to classify each trip and add a business purpose. Keep backups and make sure the data is exportable in a readable format.
Sampling for a Regular Route
If you drive a repeating route on a fixed schedule, the IRS allows you to log a representative sample period and extrapolate to the full year. You have to show the sample reflects your typical driving pattern, and if the route changes mid-year, the sample has to be updated. This option fits delivery drivers and service professionals with predictable weekly circuits.
What a Missing or Weak Log Costs You
Vehicle expenses sit in an unforgiving corner of tax law. For most deductions, a taxpayer with imperfect records can still claim 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 An inadequate log means no deduction, not a reduced one.
The fallout extends past the lost write-off. The underpayment of tax can trigger an accuracy-related penalty of 20% on top of the additional tax owed.5Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments The statute treats failure to make a reasonable attempt to comply as negligence, and failing to keep adequate records is a textbook example. Interest runs on the unpaid balance from the original due date of the return.
A taxpayer who acted in good faith and had reasonable cause for the shortfall may avoid the penalty, but not knowing about the log requirement is a weak argument when it appears 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 depreciate the vehicle under the actual expense method, keep the mileage logs and related records until three years after the year you stop claiming depreciation, whether the vehicle is fully depreciated, sold, or taken out of service. Because passenger automobile depreciation can run five or more years, that often means holding first-year records for 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, and your records need to survive the full window.
You don’t file the log with your return. You keep it and produce it if the IRS asks.
A Note on Who Can Use the Deduction in 2026
Keeping a flawless log only matters if you’re eligible to claim the deduction. Self-employed taxpayers, independent contractors, and sole proprietors deduct vehicle expenses directly on Schedule C with no floor. The Tax Cuts and Jobs Act eliminated the itemized deduction for unreimbursed employee expenses from 2018 through 2025, and that provision expired on December 31, 2025, so W-2 employees who itemize can again deduct unreimbursed vehicle expenses for 2026, subject to the 2% of adjusted gross income floor on miscellaneous deductions.8Congress.gov. Expiring Provisions in the Tax Cuts and Jobs Act (TCJA, P.L. 115-97) For most employees with modest driving, that floor absorbs the full deduction.
Four employee categories can file Form 2106 without the 2% threshold: Armed Forces reservists, qualified performing artists, fee-basis state or local government officials, and employees with disabilities claiming impairment-related work expenses.9Internal Revenue Service. Instructions for Form 2106 The logging rules are the same for every one of these filers. What changes is where the deduction lands and whether a floor eats it.