Every January the same thing happens: people who drove for work all year sit down to do their taxes and discover they never kept a mileage log. The honest answer is that a log written from memory in March is the weakest record there is — but a log rebuilt from evidence you already have is a different thing, and it is the only version worth building.
The rule in one sentence: you can't estimate vehicle miles, but you can reconstruct trips from records made at the time — calendars, invoices, receipts, location history — as long as every entry points to the evidence behind it.
Why estimates don't work for car expenses
For most business expenses, courts sometimes accept a reasonable estimate when records are missing. Car expenses are the exception: vehicles are listed property under §274(d), which requires strict substantiation. "About 8,000 business miles" is not a record, and an auditor is not required to accept any part of it.
What §274(d) asks for is proof of each element — date, miles, destination and business purpose — either through adequate records kept at or near the time, or through your own statement backed by sufficient corroborating evidence. A reconstruction lives in that second category: it is only as strong as the evidence each line can point to.
Evidence that can rebuild a trip
- Calendar entries with a client, address or meeting — the best source for business purpose and date.
- Invoices, job tickets and appointment records that name a client site and a date.
- Location history — a Google Maps Timeline export records where the phone actually went, with times.
- Receipts for parking, tolls or fuel that carry a place and a time.
- Odometer readings from service records, inspections or a dealer — the year's total that every reconstructed mile has to fit inside.
How to rebuild it, step by step
- Fix the year's total first. Find an odometer reading near January 1 and one near December 31 (a service invoice is fine). Your business miles can't exceed the difference — and if they come close to all of it, expect questions.
- List trips only where you have evidence. One line per trip: date, from, to, purpose, and the evidence it came from ("calendar: Rivera kitchen bid"). No evidence, no line.
- Measure each distance with a mapping service between the two addresses, and keep it as measured — don't round up.
- Separate commuting. Home to a regular workplace is personal, even on a work day. Leaving it in is the fastest way to lose credibility.
- Label it. Mark the log as reconstructed from records and keep the evidence with it. A reconstruction presented as if it were kept at the time does far more damage than one that says what it is.
When you only have part of the year
Publication 463 lets you substantiate a whole year from an adequate representative portion of it — for example, a complete record for one week of each month — when you can show the sample is representative of the year. That is not permission to extrapolate from a good week; it works when your driving genuinely follows a pattern and the sample proves it.
Doing it in Mile
Mile can turn your Google Maps Timeline export into drives on the phone — every row is marked Imported, never presented as recorded by Mile — and named places, the commute check and Smart Review help you sort business from personal quickly. Every PDF report states how many drives were imported from earlier records, and the year's audit binder carries a verification code that shows exactly that split. Then leave automatic tracking on, so next January the log already exists.
This guide explains IRS record-keeping rules in general terms; it is not tax advice.
Sources
- IRS, Publication 463 — Travel, Gift, and Car Expenses (Chapter 5: Recordkeeping — adequate records, sufficient evidence, sampling)
- IRS, Topic No. 510 — Business use of car
- 26 USC §274(d) — substantiation required for listed property, including vehicles