A mileage log survives an audit when it was written at the time, records each trip separately, and can say why every business mile was a business mile. That is the whole standard. Everything else — the app you use, the format you export, whether you track in miles or kilometres — is detail. What follows is what auditors actually look at, and the habits that produce a log they accept.
What does a tax authority actually ask a mileage log for?
Four things, per trip: when it happened, how far it was, where it went, and why it was business. A year-end total on its own answers none of them. Auditors do not start from the assumption that your number is wrong — they start from the question of whether the number is supported, and a single figure with nothing behind it is unsupported by definition.
The "why" matters as much as the "how far". A trip record that says 14 kilometres on a Tuesday is a fact about your car; a trip record that says 14 kilometres delivering food orders is a fact about your business. Tax systems differ in wording — the IRS, HMRC and the CRA each publish their own record-keeping guidance — but the shape of what they ask for is remarkably consistent.
- Date and time of each trip
- Distance driven, per trip rather than per week
- Start and end points
- The business purpose of the trip
What does "contemporaneous" mean, and why do auditors care?
It means recorded at or near the time of the trip, and auditors care because memory is the weakest form of evidence there is. A log rebuilt in April from a calendar and a fuel-card statement is a reconstruction, and reconstructions have a familiar signature: round numbers, identical repeated trips, and suspiciously few personal miles. Auditors have read thousands of logs. The signature is easy to spot.
A contemporaneous log looks different because reality looks different. Distances are uneven. Some days have eleven trips and some have two. There are personal drives mixed in, classified as personal. That texture is not noise to be cleaned up — it is exactly what makes the log credible. The practical rule: the closer to the moment of driving a record is made, the more it is worth, which is the strongest argument for recording trips automatically rather than remembering to.
Why do endpoints and routes matter if the distance is right?
Because the distance is only as believable as what sits behind it. A claimed 18 kilometres between two points that are 6 kilometres apart invites a question; a stored route showing the actual roads driven answers it before it is asked. Endpoints and routes are the difference between asserting a number and evidencing one.
Endpoints also police the boundary of the trip itself. A delivery drive ends where the vehicle parked — not at the customer’s door after a walk across a car park and up three flights of stairs. Distance recorded past the parking spot quietly inflates every trip, and a log that is systematically flattering in small ways reads as unreliable in large ones. If your tracking trims the walk and anchors the trip where you parked, that discipline is visible in the data, and it works in your favour.
What sinks a mileage log in practice?
Almost always one of five things, and none of them is arithmetic.
None of these is fatal on its own. Together they describe a log that was produced for the audit rather than kept for the business — and that impression, once formed, colours how everything else you submit is read.
- Gaps: weeks with no entries at all, then a burst of tidy records
- Round numbers everywhere: trips of exactly 10, 15 and 20, day after day
- No personal miles: a car that apparently never drove to a supermarket
- Missing purpose: distances with no note of what the driving was for
- Totals only: a yearly figure with no per-trip records behind it
How do you record a business purpose without writing an essay?
A few words, applied consistently, are enough: "food delivery", "passenger trips", "parcel route", "client visit". The purpose does not need to be unique per trip — most gig work is the same purpose repeated — it needs to be present per trip, so that no auditor has to guess. If you drive for more than one platform, noting which platform a shift served makes the log stronger still, and makes your own per-platform earnings math possible as a side effect.
The trap to avoid is deferring it. "I will add purposes later" produces the reconstruction problem all over again, one field at a time. Capture the purpose when the trip is filed — which, if trips are filed with a swipe at the end of a shift, costs you nothing.
What is the easiest way to keep all of this without thinking about it?
Automate the recording and keep the classifying as a small manual habit. The four fields auditors want are exactly what an automatic GPS tracker captures on its own: date, distance, endpoints and route, recorded contemporaneously because the phone was there when the driving happened. What remains for you is the one judgment a tracker cannot make — was this business? — and that is a swipe, not a spreadsheet session.
For the mechanics of what automatic tracking records and what it deliberately leaves out, see the comparison of automatic and manual tracking elsewhere on this blog; for the judgment calls themselves, the guide to classifying business, commuting and personal drives covers the categories auditors expect you to keep apart.