How to keep a mileage log for taxes
What a mileage log needs to contain, the three ways to keep one, and how to make your business-mile deduction survive scrutiny.
Why the log matters (and the contemporaneous rule)
Business-mile deductions are only worth something if you can back them up under scrutiny. IRS Publication 463 requires a "contemporaneous" log — meaning recorded at or near the time of the trip (Treasury Reg. § 1.274-5T). A log recorded in real time beats a reconstructed Excel sheet every time. When audits disallow mileage deductions, the #1 reason is lack of timely, contemporaneous records.
The 4 things IRS Publication 463 requires
Under IRS guidelines, every single business trip record must contain four specific data points:
1. Date: The day the trip occurred.
2. Mileage: The exact distance driven for the business trip, plus your total miles for the year.
3. Destination / Locations: Where you started and where you went (addresses or recognized business locations).
4. Business Purpose: The specific business reason for the drive (e.g., client consultation, job site inspection, parts run).
Missing even one of these four elements turns a deductible mile into an unsubstantiated expense.
Three ways to keep a mileage log
Paper notebook— free, and it works, but only if you remember to write in it after every single drive. Most people don't.
Spreadsheet— more flexible, easy to total up at month's end, but still manual entry for every trip. It survives exactly as long as the habit does. Reconstructing a year of drives into a spreadsheet the week before filing is easily flagged in an audit.
Automatic app — captures the drive automatically via background GPS, which solves the forgetting problem and creates a true contemporaneous record. The trade-off moves elsewhere: now you need a way to sort business drives from personal ones without reviewing every trip by hand.
The classification problem nobody mentions
Capturing drives automatically is the easy part — most apps do that now. The part that actually determines whether you keep the log going is what happens next: sorting each trip into business or personal. Left unclassified, drives pile up into a backlog that gets skipped at tax time, which is the same outcome as never logging them at all.
What to hand your accountant at tax time
A clean export — one row per trip, with the date, start and end locations, distance, classification, mileage rate, and deduction amounts — is enough for most accountants to work from directly. A CSV file opens in Excel, Google Sheets, or tax preparation software.
Frequently asked questions
What does a mileage log need to include?
At minimum, each trip needs a date, a start and end location, the distance driven, and the business purpose. Missing any one of these turns a clean deduction into a guess.
Is a spreadsheet good enough for a mileage log?
A spreadsheet is more flexible than a paper notebook and easy to total up at month's end, but it still requires manual entry for every trip. It survives exactly as long as the habit does.
What should I give my accountant at tax time?
A clean export — one row per trip, with the date, locations, distance, classification, mileage rate, and deduction amounts — is enough for most accountants to work from directly. A CSV file opens in anything they already use.
This is general information, not tax advice. Consult a qualified professional for your specific filing decisions.
Track it automatically instead.
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