What Counts as a "Contemporaneous" Mileage Log to the IRS

"Contemporaneous" does not mean instant, and it does not mean perfect. It means the log was built at or near the time of each drive, not assembled months later from memory when a client's return is due. That distinction decides whether a preparer can rely on a client's numbers or has to push back on them.

Source: IRS Publication 463, Travel, Gift, and Car Expenses, the substantiation standard under Internal Revenue Code section 274(d).

Where the standard actually comes from

Section 274(d) singles out vehicles as "listed property" and requires adequate records or sufficient evidence to corroborate the taxpayer's own statement, for the amount, time, place, and business purpose of each use. Publication 463 translates that into practice: a log, diary, or similar record made at or near the time of the expense, backed up by documentary evidence like receipts where relevant. The IRS does not require an entry logged the same day. It does require that the record was built close enough to the drive that it reflects the driver's actual memory of it, not a reconstruction built for the audit.

Why Cohan does not rescue a bad mileage log

Every preparer eventually hears about the Cohan rule, from Cohan v. Commissioner (2d Cir. 1930), which lets a court estimate a deductible expense when records are missing but the expense clearly happened. It does not apply here. Congress amended section 274(d) specifically to override Cohan for travel, entertainment, gifts, and listed property, vehicles included. The Tax Court has said this directly in multiple mileage cases: no log, no estimate, no deduction, no matter how plausible the driving sounds. A client who says "I definitely drove 15,000 miles for the business, just trust me" has zero deduction under section 274(d), not a negotiable one.

What a contemporaneous log has to show

• The date of each trip
• Where the driver went (or the odometer reading at start and end)
• The business purpose, specific enough to mean something six months later
• Total miles for the trip

What still counts as contemporaneous, even if it is not daily

A driver who logs each trip in an app the same day, or within a few days, is contemporaneous. A driver who updates a spreadsheet every Sunday night from memory of that week's trips is a closer call but generally accepted in practice, since the gap is short and the record predates any audit. A driver who sits down every March to reconstruct the prior year from bank statements and a general sense of their routes is not contemporaneous, whatever the numbers say. Automatic GPS-based tracking removes the argument entirely, because the record is created by the drive itself.

The preparer's practical test

Before you accept a client's mileage total, ask when the log was created relative to the driving. If the answer is "I built this list last week for our appointment," that is not a contemporaneous log, even if every number in it turns out to be accurate. It is a reconstruction, and it needs the different, higher-risk treatment covered in reconstructing a client's missing mileage log defensibly rather than a clean pass-through onto Schedule C.

How this plays out in an actual examination

An examiner reviewing a mileage claim typically asks for the underlying log before anything else, and the first thing they check is when it was created, not just what it says. A log an app time-stamps entry by entry answers that question automatically. A spreadsheet with no creation history behind it invites a follow-up question the taxpayer may not be able to answer well: prove this was built during the year, not last week. That single follow-up is where a contemporaneous-looking log that is not actually contemporaneous falls apart, and it is why the timing question matters more than the format of the record.

Does a contemporaneous log have to be on paper?

No. A phone app, a spreadsheet updated close to the driving, or a paper notebook all qualify, as long as the record was made at or near the time of the trip. Format does not matter to section 274(d). Timing does.

What if the client only has partial contemporaneous records?

Use what is genuinely contemporaneous as-is, and treat the gaps as a separate reconstruction problem rather than blending the two into one number. Mixing a solid logged period with a guessed period without labeling the difference is how an otherwise defensible log becomes an indefensible one under examination.

Does switching mileage apps mid-year break the contemporaneous chain?

No, as long as each app's export shows entries made close to the actual driving. Keep both exports on file and note the switch date, so the record reads as two contemporaneous periods back to back rather than one confusing file.

Recommend a tool that builds the contemporaneous record automatically, so the question of timing never comes up. Try TruMile →

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