Records · All four countries
Mileage log requirements: what actually survives an audit
The rate is the easy part. Mileage claims fail in audits over records — missing purposes, logs rebuilt from memory, round numbers that smell invented. Here's what each authority requires, where the rules differ, and the failure patterns auditors look for.
The fields every log needs
| Field | US (IRS) | UK (HMRC) | Canada (CRA) | Australia (ATO) |
|---|---|---|---|---|
| Date of trip | Required | Required | Required | Required |
| Start & end points | Destination required | Required | Required | Required (logbook method) |
| Distance | Required | Required | Required | Required |
| Business purpose | Required | Required | Required | Required |
| Odometer readings | Year start/end recommended | Not required | Year start/end required | Required for logbook method |
| Total annual km/miles | Required (business + total) | Business total required | Required (business + total) | Required for logbook % |
The pattern is obvious once you see it: four columns, one log format. A single record style — date, from, to, distance, purpose — satisfies everyone, which matters if you drive in more than one country or build a template for a team.
United States: "contemporaneous" is the whole game
The IRS doesn't just require a log; it requires one made at or near the time of the trip. That word — contemporaneous — decides cases. A spreadsheet updated weekly from a calendar passes. A log assembled eighteen months later, when the audit letter arrives, generally doesn't, and when it fails, the entire deduction goes with it, not just the sloppy entries. Tax Court mileage cases are a graveyard of reconstructed logs.
Practical standard that holds up: record each trip within a few days, note the business purpose specifically ("client meeting — Hendricks account," not "work"), and capture your odometer on January 1 and December 31 so total mileage is provable. Parking and tolls ride on top of the standard rate — keep those receipts separately.
United Kingdom: journey records, not fuel receipts
HMRC's AMAP system deliberately removes receipts from the picture — the per-mile rate replaces them. What it doesn't remove is the journey record: date, start and end, miles, purpose, for every business trip. Employers paying mileage need these to justify tax-free treatment; employees claiming Mileage Allowance Relief on a shortfall need them to support the claim, especially relevant in 2026/27 with the backdated 45p→55p change generating back-claims.
The trap to document carefully is the commuting boundary. Travel to a permanent workplace never qualifies; travel to a temporary one can — and the 24-month rule that separates them turns on facts your log should capture (where, how often, over what period).
Canada: the full logbook, then the shortcut
The CRA expects a full logbook — every business trip, plus odometer readings at the start and end of the year — and it's the safest evidence for both employees justifying allowances and the self-employed deducting actual costs.
Canada also offers something the other three don't: an official shortcut. After you've kept one complete 12-month logbook (the "base year"), the CRA accepts a three-month sample logbook in later years, scaled up — provided the result stays within 10 percentage points of the base year's business-use proportion. It's the lowest-effort compliant regime of the four, but only after you've earned it with the base year. Skip the base year and the sample means nothing.
Australia: two methods, two record standards
The cents-per-km method advertises "no logbook," which people mishear as "no records." You still need a defensible basis for the kilometres claimed — a diary of trips, an app log, or a documented calculation (the ATO's own style of example: a 20 km weekly round trip × 48 working weeks = 960 km). Round-number claims sitting exactly at the 5,000 km cap with no supporting basis are a known audit flag.
The logbook method demands more and pays more: a continuous 12-week logbook recording every trip, business and private, with odometer readings — which then establishes a business-use percentage you can apply to actual costs for up to five years, as long as usage stays representative. Twelve weeks of discipline, five years of value.
How long to keep everything
| Country | General retention rule |
|---|---|
| United States | About 3 years from filing in ordinary cases; substantially longer where large understatements or fraud are in play. Many advisers say keep vehicle logs 7 years. |
| United Kingdom | Employees: about 22 months after the end of the tax year. Self-employed: about 5 years after the 31 January filing deadline. |
| Canada | 6 years from the end of the tax year the records relate to. |
| Australia | 5 years from the date you lodge the return that relies on them. |
The five ways logs fail audits
Reconstruction. Built after the fact, usually obvious from uniform handwriting, identical round trips, or metadata. Vague purposes. "Errands" and "meeting" don't connect a trip to income. Round numbers. Twelve months of trips that all end in zero reads as estimation. Impossible totals. Claimed business miles that exceed what the odometer says the car drove at all — auditors check service records for odometer history. Commuting smuggled in. The home-to-regular-workplace run claimed as business; every authority tests for it first because it's the most common inflation.
The fix for all five is the same boring habit: log within days, be specific, and let the odometer anchor the totals.
Primary sources
- IRS, Publication 463 (Travel, Gift, and Car Expenses) — record-keeping chapter
- GOV.UK, expenses and benefits: business travel mileage guidance; record-keeping for Self Assessment
- CRA, motor vehicle records guidance (full and simplified logbook), via canada.ca
- ATO, cents per kilometre method and logbook method pages
General information, not tax advice. Audit standards involve judgment and case law beyond any summary — when real money is at stake, involve a professional early.