A mileage log book for taxes is a written record of every business trip you drive, kept close to the time of travel, showing the date, the miles, where you went, and why. The IRS requires this documentation from anyone claiming a vehicle deduction, and a log that meets the standard is what separates a defensible deduction from one an auditor throws out. For 2026, each properly logged business mile is worth 72.5 cents against your taxes.1Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate at 72.5 Cents Per Mile, Up 2.5 Cents
What Your Log Must Contain
Federal law requires you to substantiate four things for every trip: the amount of the expense, the time, the place, and the business purpose.2Office of the Law Revision Counsel. 26 US Code 274 – Disallowance of Certain Entertainment, Etc., Expenses Translated into log entries, each row needs:
- The date of the trip.
- Odometer readings at the start and end, which establish the actual distance driven.
- The destination, specifically enough to identify it, such as a client’s office address or a supply warehouse.
- The business purpose, described concretely. “Client meeting with ABC Corp regarding Q2 contract” holds up. “Business” does not.
Log parking fees and tolls as separate line items on the same day. Those are deductible on top of the standard mileage rate, but only if you can document them.3Internal Revenue Service. Topic No. 511, Business Travel Expenses If you forget to check the odometer, a mapping tool can supply the distance between the two addresses as a backup. It’s acceptable occasionally. Rely on it habitually and your log weakens.
Timing: The Contemporaneous Rule
The IRS expects records made “at or near the time” of each trip. A weekly log covering that week’s driving qualifies as timely. Sitting down in April to piece together a year of driving from calendar entries does not.4Internal Revenue Service. Publication 463 – Travel, Gift, and Car Expenses
Reconstructed logs aren’t automatically disqualified, but they’re far more vulnerable to challenge, and you’ll need corroborating evidence like emails, invoices, and appointment records to prop them up. The stakes go beyond losing the deduction. If the IRS finds your records inadequate and disallows the mileage, the resulting underpayment can carry an accuracy-related penalty of 20%.5Internal Revenue Service. Accuracy-Related Penalty Keep the log in the vehicle or on your phone so writing entries becomes reflexive.
Which Miles Count
The IRS draws a hard line between business driving and commuting. Your daily trip from home to a regular workplace and back is a commute, and it is never deductible, regardless of distance.4Internal Revenue Service. Publication 463 – Travel, Gift, and Car Expenses Logging those miles as business is the fastest way to poison an otherwise good log.
Business miles include driving between two workplaces the same day, visiting clients or customers, going to a meeting away from your regular office, and running work errands like picking up supplies. Driving from your regular office to a client across town is a business mile. Driving from your house to that same office is not.
Two exceptions matter. If you travel from home to a temporary work location and you have a regular workplace elsewhere, that trip counts as business mileage; the IRS treats a location as temporary if you expect to work there for less than a year. And if your home qualifies as your principal place of business, every trip from your home office to a client, supplier, or coworking space is a business mile rather than a commute.
Odometer Readings at Year Start and End
Record your odometer on January 1 and December 31, or on the first and last days you use the vehicle for business that year. Schedule C asks for total miles driven, not only business miles, and the only way to report that number is to know where the odometer started and ended. Build the reading into your routine the way you would a beginning balance in a checkbook.
Paper, Spreadsheet, or App
The IRS doesn’t mandate a format. A bound notebook with columns for date, odometer readings, destination, and purpose works. So does a spreadsheet, which handles totals automatically. GPS-based smartphone apps go further by detecting when you start and stop driving, logging the route, and letting you tag each trip as business or personal. The main practical problem with mileage logs is remembering to make entries, and apps solve that for most trips.
Whichever format you use, keep supporting documentation alongside it. Publication 463 recommends documentary evidence, such as receipts, for the expenses recorded in your log.4Internal Revenue Service. Publication 463 – Travel, Gift, and Car Expenses Transportation expenses without a readily available receipt are one of the specific exceptions, so you don’t need gas receipts if you’re using the standard mileage rate. Keep toll and parking receipts when you can.
How Long to Keep the Log
The general rule is three years from the date you filed the return claiming the deduction. If you underreport gross income by more than 25%, the window stretches to six years.6Internal Revenue Service. How Long Should I Keep Records
Three years is the floor. Six or seven years as a default costs nothing and removes any risk of destroying something you turn out to need. Back up digital logs in at least one additional location, whether cloud storage or a separate drive. Scan paper logs into a PDF archive once the tax year closes.
Who Can Actually Use the Log for a Deduction
Self-employed people, independent contractors, and sole proprietors are the main group who can claim business mileage. If your income is reported on Schedule C, you’re in this group.
For W-2 employees, the deduction is largely gone. The Tax Cuts and Jobs Act suspended unreimbursed employee business expenses starting in 2018. Through the 2025 tax year, only four narrow categories of employees could still deduct vehicle expenses on Form 2106: Armed Forces reservists, qualified performing artists with adjusted gross income of $16,000 or less, fee-basis state or local government officials, and employees with impairment-related work expenses.7Internal Revenue Service. Instructions for Form 2106 The TCJA provisions were set to expire after 2025, so 2026 rules may shift depending on what Congress does. If you’re a regular employee whose employer doesn’t reimburse mileage, confirm the current law before assuming you can deduct.
Even if your eligibility is uncertain, keep the log. If rules expand mid-year, you’ll need records dating from January, not from the day you learned you qualified.
The 2026 Rate and How the Log Feeds Your Return
For tax year 2026, the standard mileage rate is 72.5 cents per business mile, up from 70 cents in 2025. The rate applies equally to gasoline, diesel, hybrid, and electric vehicles.1Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate at 72.5 Cents Per Mile, Up 2.5 Cents Ten thousand logged business miles produces a $7,250 deduction.
Self-employed taxpayers report vehicle expenses on Schedule C. Part IV asks when the vehicle was placed in service, total miles driven for the year, and how many were business miles.8Internal Revenue Service. Schedule C (Form 1040) – Profit or Loss From Business Your log is the direct source for those numbers. The form also asks whether you have written evidence supporting the deduction and whether that evidence is contemporaneous. Answering no to either doesn’t automatically trigger an audit, but it does raise a flag. The small number of employees still eligible use Form 2106, which separates business miles from commuting miles and applies the standard mileage rate or actual expenses.7Internal Revenue Service. Instructions for Form 2106 The recordkeeping standard is the same on either form.