Forgot to Keep a Mileage Log? What Reconstruction Can and Can't Do
General information, not tax or legal advice. Talk to your tax preparer about your situation.
You can try to rebuild a mileage log, but a reconstruction carries less weight than a record kept at or near the time (IRS Pub 463). Without adequate records, you have to support each element with your own statement and other evidence, such as calendars, invoices and service records. Logs built from averages often fail. Talk to your preparer.
It's March, the preparer wants business miles, and there is no log. You're not alone; this is one of the most common situations self-employed drivers end up in. Here is what IRS guidance says about records, what a reasonable rebuild draws on, and the limits of what any reconstruction can do.
What the IRS asks for
IRS Publication 463 says you can't deduct car expenses unless you can prove them with adequate records or sufficient evidence that supports your own statement. For car use, the elements are the amount (mileage for each business use and total miles), the time (date), the place (destination) and the business purpose. The Form 2106 instructions describe the same substantiation rules under Internal Revenue Code section 274(d).
Timely-kept records carry the most weight
Pub 463 says a record of the elements made at or near the time of the use, supported by documentary evidence, has more value than a statement prepared later. It also treats a log kept weekly as timely kept.
If you don't have adequate records
Pub 463 says that if you don't have complete records, you must prove each element with your own written or oral statement containing specific information, plus other supporting evidence. A rebuilt log is that statement. Its strength depends on what you can tie it to.
Evidence a rebuild can draw on
- Calendar entries, appointment apps and email confirmations showing where you were and why.
- Invoices, receipts and client records with dates and addresses.
- Service and inspection records showing odometer readings at known dates.
- Your car's own trip history or app data, if it was recorded at the time.
- Platform trip statements for rideshare or delivery work.
- Map distances for each documented trip, not round-number estimates.
Records lost for reasons beyond your control
Pub 463 says that if your records were lost because of circumstances beyond your control, such as fire or flood, you can prove a deduction by reconstructing your records or expenses. That's different from never keeping records.
Why logs built from averages fail
Tax Court cases summarized in professional publications show a pattern: logs reconstructed from typical-day averages, without dates, destinations or purposes for specific trips, are often given little weight, and the deduction is reduced or disallowed (NSTP summary; HR Daily Advisor). Each case turns on its facts, so treat this as a reason to document, not as a prediction.
A careful way to rebuild
- Pull your calendar, invoices and service records for the year.
- List only trips you can tie to a specific document: date, place, purpose.
- Measure each trip's distance with a map rather than estimating.
- Check the total against odometer readings from service records.
- Mark the log as reconstructed and keep every supporting document with it.
- Leave out trips you can't support.
Your preparer decides how to use it. Don't present a rebuilt log as if it were kept at the time.
What it means for the numbers
Whatever method you use, the deduction starts from supported business miles. For 2026 the standard rate is 72.5¢ per mile for January 1 to June 30, 2026 (IR-2025-128 / Notice 2026-10) and 76¢ per mile for July 1 to December 31, 2026 (IR-2026-29 / Announcement 2026-11) (IRS standard mileage rates page).
Example: 1,000 hypothetical, documented business miles in May 2026 × 72.5¢ (IR-2025-128) = $725 at the standard rate. Undocumented miles add nothing you can support. Estimates, not tax advice.
Start a log made at the time, today
The fix for next year is a record kept as you go. CyberDeduct builds the log from the car's telemetry as you drive, with start and end odometer readings from the car, so the record exists at the time of the trip; you confirm the purpose.
CyberDeduct builds a mileage log around IRS Pub 463 from your Tesla's own trip and odometer data. You connect your Tesla account once through Tesla's standard account sign-in (OAuth); CyberDeduct never sees or stores your password. You confirm each trip's purpose and export a PDF or CSV log plus a Form 4562 Part V worksheet for your tax preparer. See how the log is built or see plans.
Frequently asked questions
Can I reconstruct a mileage log after the fact?
You can, but it carries less weight than a timely-kept record. Without adequate records you have to support each element with your own statement and other evidence (IRS Pub 463).
What evidence helps a reconstructed log?
Calendars, invoices, client records, service records with odometer readings, platform statements and car trip data recorded at the time.
What if my records were destroyed?
Pub 463 allows a reasonable reconstruction when records are lost for reasons beyond your control, such as fire or flood.
Can I use an average daily mileage?
Tax Court cases often give little weight to logs built from averages without trip-level details. Talk to your preparer.
How often should I update my log?
Pub 463 treats a log kept weekly as timely kept.
This article is general information, not tax or legal advice. Talk to your tax preparer about your situation.
CyberDeduct is an independent product of LIKE LLC and is not affiliated with or endorsed by Tesla, Inc. Tesla is a trademark of Tesla, Inc.