Guides / Taxes
What the IRS actually wants in a mileage log.
Almost nobody loses the mileage deduction because they did not drive. They lose it because, a year later, they cannot prove they drove. The rules for what counts as proof are unglamorous, specific, and much easier to satisfy in the moment than to reconstruct afterwards. Here they are.
The four things every entry needs
For car and transportation expenses, you have to be able to establish four elements. Miss one and the entry is weak, however honest it is:
- Amount — how far you drove. Miles, not a dollar figure.
- Time — the date of the trip.
- Place — where you went. A destination, not "around town".
- Business purpose — why. This is the one people skip, and it is the one that gets asked about.
Alongside the trip entries, keep the odometer reading at the start and end of the year. That gives you total miles for the vehicle, which is what business-use percentage is calculated against — and it is the first thing anyone checking your return will want to reconcile your log to.
"Timely kept" is doing a lot of work
The standard is a timely kept record — one made at or near the time of the trip, while you still remember it. A log written in the moment is treated as far more credible than one assembled at tax time, and that difference is the entire reason to bother logging as you go.
You are allowed to write up a log later. But a spreadsheet built in March from memory and map history is exactly the kind of evidence that invites more questions rather than closing them. If your log has to be defended, the date it was created matters almost as much as what it says.
You may not have to log all 12 months
Sampling is permitted: keep a detailed log for a representative part of the year and use it to support the full year, as long as the sample honestly reflects your driving. That is a real convenience — and a trap for anyone whose work is seasonal, lumpy, or growing. A strong November does not prove a quiet February.
If your driving is uneven, log the whole year. It is less work than defending a sample that does not hold up.
Commuting is not business mileage
Driving between home and your regular place of work is commuting, and commuting is not deductible — no matter how far it is or how self-employed you are. Trips between job sites, out to clients, to pick up supplies, or to the bank for the business generally do count. The line matters, because a log that quietly folds the commute in is worse than no log: it makes the rest of the entries look unreliable too.
How good logs go bad
The failures are boringly consistent. Watch for these in your own records:
- Suspiciously round numbers. Every trip 10 or 25 miles is a pattern no real week produces.
- No stated purpose. "Client" is not a purpose. "Site visit — Harper kitchen remodel" is.
- Gaps. Three logged weeks in a twelve-week quarter reads as an estimate wearing a log's clothes.
- Business and personal blended. If the two are not separated, none of it is clean.
- A total with nothing behind it. "14,200 business miles" is a claim, not a record.
What a good entry looks like
Weak
March — client visits — 300 miles
Strong
12 Mar 2026 · 31.4 mi · office → Harper residence, Bellevue · on-site measure for kitchen remodel quote
The second one takes about eight seconds to record at the time, and it answers every question the first one provokes.
Keep it for three years
Three years is the general window for a return to be examined, so that is the floor for keeping mileage records. Hold them longer if you are depreciating the vehicle or carrying anything forward — and keep them somewhere that survives a lost phone, because "it was in an app I deleted" is not a filing position.
One more thing about 2026
2026 has two standard mileage rates, not one: 72.5¢ per mile through 30 June, and 76¢ from 1 July. If you are using the standard rate, your log needs to support a clean split at that date — another reason dated entries beat an annual total. The full rundown of the deduction covers the rest.
This guide is general information, not tax advice. Substantiation rules and rates change; verify current requirements at irs.gov — Publication 463 is the source for the record-keeping rules above — and talk to a tax professional about your own situation.
Four fields, filled in as you drive.
OdometerIQ records the date, distance, destination and purpose on each trip, keeps odometer photos, and exports the year as a PDF and CSV.