Mileage Substantiation When a Client's Deduction Goes to Deposition

A mileage log that is good enough to file a return is not automatically good enough to survive being questioned under oath. When a client's business mileage becomes an issue in a Tax Court appeal, a divorce proceeding, or a contract dispute over reimbursement, the substantiation standard the record actually has to meet gets a lot higher, and it is worth knowing that gap before a client walks into a deposition unprepared.

Source: IRS Publication 463, on the section 274(d) substantiation standard, and general practice in Tax Court examination of mileage claims.

Why litigation raises the bar past a routine filing

Most mileage logs are never tested by anyone. They sit in a client's file, support a Schedule C number, and are never opened again. In a Tax Court appeal, a divorce case where mileage feeds an income-imputation argument, or a dispute over an employer's reimbursement obligation, the log becomes an exhibit, subject to cross-examination on exactly when each entry was made, what evidence backs the dates, and whether the record was altered after the fact.

The questions a log has to survive under examination

• When was each entry actually created, and can that be proven independently of the client's testimony?
• Does the app or system have a metadata trail showing the entry date, not just the trip date the user typed in?
• Are there gaps, edits, or backdated batches of entries visible in an export history?
• Does the total reconcile against odometer readings, fuel purchases, and other independent records for the same period?

Why an automatic, GPS-based log holds up better in this setting

A manually typed log is only as strong as the client's own testimony about when it was written, which opposing counsel can and will challenge directly. A GPS-based tracking app generates a timestamped record independent of the user's memory, with metadata showing exactly when each trip was captured, not just the date the user later assigned to it. That independence is the difference between a log that supports a client's testimony and a log that is the client's testimony, unverifiable either way.

What a preparer or advisor should flag before a dispute escalates

If you become aware a client's mileage deduction is likely to be contested, litigation, a formal audit, a reimbursement dispute with an employer, pull the underlying record early and assess it against the questions above, before the client is asked about it in a formal setting. A log with genuine gaps or inconsistencies is better identified and explained by the client's own advisor first than discovered by opposing counsel during a deposition.

Expert review, when the stakes justify it

In high-dollar disputes, a forensic review of the underlying app data, export timestamps, GPS breadcrumbs, device logs, can establish authenticity in a way a printed spreadsheet cannot. This is not warranted for a routine return, but it is a real option worth raising when a client's mileage substantiation is central to a contested six-figure claim.

How opposing counsel actually attacks a mileage log

The attack rarely targets the miles themselves first. It targets the log's creation history, when each entry was actually made, whether the export can be edited after the fact without leaving a trace, and whether the client can explain any single entry without looking at the log. A client who can talk through a handful of specific entries from memory, in a way that lines up with what the record shows, is far more credible under questioning than one who can only say "that's what the app says."

Does a reconstructed log ever survive litigation-level scrutiny?

It can, if it is built from strong independent corroboration, calendars, client records, service receipts, per how to reconstruct a client's missing mileage log defensibly, but it starts from a weaker position than a contemporaneous, independently timestamped record and should be presented to the client with that caveat before any dispute begins.

Should every client be told their log might end up in litigation?

No, but every client with a meaningful mileage deduction benefits from a record that would hold up if it ever needed to. Recommending a contemporaneous, GPS-based log serves that purpose without requiring the conversation to be framed around litigation risk specifically.

Who typically requests the underlying app export in these disputes?

Opposing counsel, a court-appointed examiner, or an IRS agent conducting a formal audit can all request the underlying data, not just the summary total the client originally filed with.

Could the preparer themselves be asked to testify about the log?

It happens, especially if the preparer helped reconstruct a gap or advised on which categories of driving to include. Keep your own notes on any reconstruction work performed, dated and specific, in case you're the one being asked to explain the record later.

For any client whose mileage might end up as evidence rather than just a tax-return input, the strongest record is the one nobody has to argue about later. Recommend automatic, timestamped tracking for any client with meaningful mileage at stake. Try TruMile →

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