What Should a Mileage Log Include for Tax Purposes?
A running odometer total tells almost nothing about why a trip was taken, which is exactly the gap a proper mileage log is meant to fill.
The short answer
A mileage log kept for tax purposes generally needs, for each trip, the date, the starting and ending locations, the business purpose, and the number of miles driven. A single lump total of miles for the year, without that supporting detail, is typically not treated as sufficient documentation on its own. The log is also expected to be kept contemporaneously — noted at or close to the time of the trip — rather than reconstructed from memory later.
Why a running total isn’t enough
It’s tempting to jot down one number at the end of the year based on a rough estimate, but that approach leaves no way to distinguish business driving from commuting or personal errands, and no way to verify the total if it’s ever questioned. This level of detail matters most for anyone using a vehicle regularly for work, including self-employed filers reporting business income on Schedule C, where vehicle costs are a common and closely reviewed deduction category.
The core elements each entry needs
A workable mileage log generally records the following for every trip:
- Date of the trip. When the driving occurred, logged individually rather than in batches.
- Starting point and destination. Where the trip began and ended, specific enough to establish the route.
- Business purpose. A short description of why the trip was necessary — a client meeting, a supply run, a job site visit.
- Miles driven. The distance covered, ideally cross-checked against an odometer reading periodically.
Some people also track the odometer reading at the start and end of the year as a way to verify the running total against actual vehicle mileage.
Contemporaneous vs. reconstructed logs
A log kept in real time, updated after or even during each trip, tends to be viewed as far more credible than one reconstructed months later from memory or a calendar. Reconstructed logs aren’t automatically disqualified, but they generally need to be built from other supporting evidence — calendar entries, appointment records, or receipts — to fill in the gaps convincingly. Starting the habit early in the year avoids the scramble of trying to remember driving patterns from many months prior.
Choosing a method that’s easy to maintain
The format matters far less than consistency. A small notebook kept in the glove compartment, a spreadsheet updated weekly, or a mileage-tracking app that logs trips automatically can all satisfy the same underlying requirement, as long as the core details are captured for each trip rather than estimated after the fact. Whichever method is used, it pairs naturally with a broader habit of organizing receipts and records as they’re generated rather than all at once.
The takeaway
The purpose of a mileage log isn’t just to produce a number — it’s to make each trip defensible on its own, with a clear date, route, and reason. This is separate from how the mileage deduction itself is calculated, which involves its own set of rules that can change; the log is simply the record that supports whatever calculation applies. A log built trip by trip, rather than assembled after the fact, tends to hold up far better if it’s ever reviewed, and it fits naturally alongside other tax documents worth tracking throughout the year.