Forgot to Track Your Miles? How to Reconstruct a Mileage Log

It is a specific kind of October feeling: you drove all year for work, and the log you meant to keep has four entries, all from January. The deduction is real — at 2026 rates (72.5 cents per mile for January–June trips, 76 cents from July 1), 8,000 undocumented business miles is roughly $5,900 — but the record is not. Rebuilding an earlier year works the same way, priced at the rate that applied then.

Here is what can and cannot be salvaged. The short version: you cannot estimate, but you can reconstruct, and the difference between those two words decides whether the deduction survives.

Why estimating is off the table

For most business expenses, imperfect records are survivable. Courts have long applied the Cohan rule — if the expense clearly happened, a reasonable estimate can be allowed.

Vehicle expenses are the exception, on purpose. IRC Section 274(d) requires specific substantiation for vehicle use: amount, time, place, and business purpose, backed by adequate records or corroborating evidence. Congress wrote that section precisely because travel deductions were where estimates went to inflate. The practical consequence, confirmed in case after Tax Court case: “I drive about 200 miles a week for work” is worth exactly zero without records behind it.

So the task is not to produce a plausible number. It is to produce trips — dated, placed, purposed, measured — from evidence that exists outside your memory.

Step 1: anchor the total with odometer readings

Start with the denominator. Your business-use percentage needs total miles for the year, and total miles hide in paperwork you already have:

• Service records — oil changes, inspections, tire rotations. Every invoice carries an odometer reading and a date.
• State inspection or emissions reports
• Insurance renewals — many insurers record annual mileage
• Purchase or sale paperwork if the vehicle changed hands

Two readings bracketing the year give you the total. Two readings eight months apart still work — pro-rate the gap. Write down where each number came from; the sourcing is part of the record.

Step 2: rebuild the trip list from external sources

Now the numerator. The goal is a list of specific business trips, each attached to a document:

Source	What it proves
Work calendar	Client meetings with dates, names, locations
Invoices and job records	That you were at a client site, and when
Gig platform statements	Dates worked and engaged miles per day
Email threads	Site visits, deliveries, appointments confirmed in writing
Bank and card statements	Fuel stops, parking, tolls — placing you on the road, with dates
Phone location history	Route-level corroboration, if you had it enabled

Work through the year chronologically and let the documents generate the trips. “March 14 — invoice #2141, on-site install at Keller Supply” becomes a trip with a date, destination, and purpose. You are not remembering trips; you are deriving them, which is the property that makes the log defensible.

Recurring patterns help, carefully. If every Tuesday invoice shows the same client for six months, the pattern supports 26 trips — anchored to the invoices, not to “I always went on Tuesdays.”

Step 3: measure the distances

Do not estimate distances; look them up. Map the route from your base to each destination and record the round-trip figure. Use the same tool for every trip and note which one. Consistent, verifiable distances are what separate a reconstruction from a guess — and they remove the round-number pattern that reviewers read as fiction.

Watch the commute boundary while you do this: trips from home to a regular workplace are not business miles no matter how well documented, and the commuting rules decide more edge cases than people expect.

Step 4: assemble it honestly

Put the result in a spreadsheet with the standard columns — date, destination, purpose, miles, source document — and label it what it is: a reconstruction, with a note on method and a folder of the underlying evidence. A structured template gives you the columns.

The labeling is not a formality. A reconstructed log presented as contemporaneous is the single fastest way to lose an examiner’s trust — and with it, the parts of your return that were fine. A reconstruction presented as one, with sources attached, is ordinary and survivable.

Be conservative at the margins. Drop the trips you cannot source. A log that visibly excludes the doubtful cases reads as honest, and reads that way because it is.

What a reconstruction cannot fix

Three hard limits, stated plainly:

1. Trips with no external trace. The site visit that produced no calendar entry, invoice, email, or receipt is gone. This is the real cost of the missing log — typically 10–30% of actual business miles are unrecoverable.
2. The timeliness standard. Publication 463 expects records made at or near the time of the trip. A reconstruction is corroborating evidence doing its best — genuinely adequate contemporaneous records it is not, and an examiner weighs it accordingly.
3. Repeat performance. One reconstructed year with good sourcing is a repair. The same story two years running is a pattern, and patterns invite exactly the scrutiny a thin log cannot survive.

Next year, make this impossible

Every reconstruction ends with the same resolution, so make it structural instead of willpower-based. The fix is capture that happens without you: automatic detection, so the record exists before you think about it.

MileTrack does the capture layer — drives are detected in the background, classified as business, commute, or private with a swipe, and exported as PDF, CSV, or XLSX with per-trip dates, destinations, purposes, and distances. It is free, works without an account, and keeps trip history on your device by default. The Octobers stay calm; the tracking-method guide covers the weekly loop that keeps the log complete.

Related guides

• How to Track Mileage for Taxes: 3 Methods That Hold Up
• Mileage Log Requirements for IRS: What to Record and How to Store It
• Commuting vs. Business Miles: IRS Rules + 5 Worked Examples

Tax note: educational content only, not tax advice. Reconstruction outcomes depend on evidence quality — for a large or contested deduction, involve a tax professional before filing.