What a Mileage Log Has to Show to Survive an IRS Audit

For most business expenses, if you can show you spent the money and it was for the business, you are in decent shape. Cars are different. Congress put vehicle expenses in a special category with a stricter proof rule, and the IRS enforces it.

That rule is IRC Section 274(d). It is the reason a self-employed driver with an honest 20,000 business miles and no log can lose the entire deduction.

The rule: no records, no deduction

Section 274(d) denies deductions for listed property unless you substantiate them. A passenger automobile is listed property under IRC Section 280F(d)(4). The regulation that implements the rule, Treas. Reg. 1.274-5T(a), is blunt about what that means. It says Section 274(d) contemplates that no deduction will be allowed on the basis of approximations or unsupported testimony of the taxpayer, and it expressly displaces the older court-made approach that let judges estimate a reasonable amount when the exact amount could not be proved.

So "I drive about 300 miles a week for work" is not proof. It is an estimate, and estimates are exactly what this rule was written to reject.

What you have to prove

Treas. Reg. 1.274-5T(b)(6) lists the elements for listed property:

1. Amount. The amount of each business use, measured in miles for a car, and the total use of the car for the year. It also covers the amount of each separate expenditure, if you deduct actual costs.
2. Time. The date of the expenditure or use.
3. Business purpose. The business reason for the use.

Notice "total use." You need total miles for the year, not just business miles, because business use is a percentage. The simplest way to capture it is an odometer reading on January 1 and December 31, or on the day the car goes into and out of service.

How you prove it: adequate records

Under Treas. Reg. 1.274-5T(c)(1), you substantiate each element either by adequate records or by sufficient evidence corroborating your own statement. Adequate records are the safer route by a wide margin.

Treas. Reg. 1.274-5T(c)(2) defines adequate records as an account book, diary, log, statement of expense, trip sheet, or similar record, together with documentary evidence, that in combination establish each element. The log must be kept so that each entry is made at or near the time of the use, when you have full present knowledge of it.

Two details in the regulation help working drivers:

• Weekly is fine. The regulation gives the example that a log maintained on a weekly basis, which accounts for use during the week, is considered made at or near the time of the use.
• Apps count. Under 1.274-5T(c)(2)(ii)(C)(2), an adequate record generally must be written, but a record of business use of a car prepared in a computer memory device with the aid of a logging program is an adequate record.

The regulation also says a contemporaneous log is not strictly required. But it explains why you want one anyway: a record made at or near the time has a high degree of credibility, and evidence prepared later has to have a high degree of probative value to reach the same level. Reconstructing a year of driving the week before an audit is the hard way.

The IRS rarely disputes that you drove. It disputes whether you can prove how far, when, and why, with something you wrote down at the time.

What a good log entry looks like

For each business trip or work shift:

• Date.
• Starting point and destination, or the route or service area.
• Business purpose, such as "rideshare shift" or "client meeting, Smith Co."
• Miles, from odometer readings or a GPS tracking app.

Plus, once a year: beginning and ending odometer readings for total miles.

The regulation allows some shortcuts. Under 1.274-5T(c)(6)(i)(C), uses that are part of a single use, like a round trip or an uninterrupted stretch of business driving, can be accounted for by a single record. A short personal stop between two business stops, such as lunch, does not interrupt the business use. And where business purpose is evident from the surrounding facts, the regulation says a written explanation may not be required, though writing it down costs you three words.

Sampling: when you missed part of the year

Treas. Reg. 1.274-5T(c)(3)(ii) allows sampling. You can keep an adequate record for a portion of the year and use it to substantiate business use for the whole year, if you can show by other evidence that the sampled period is representative.

The examples in the regulation show both sides. A business owner who kept records for the first three months, with invoices showing business continued at the same pace, could use that 75% figure for the year. A salesman who logged only his heavy delivery week each month could not, because that week was not representative.

For gig workers whose driving swings with seasons, sampling is risky. A log from a slow month will understate the year, and one from the holiday rush will look inflated. Log the whole year if you can.

Why the app's mileage is not enough by itself

Platform mileage summaries are useful corroboration. They are not a complete log.

• They usually capture only miles while you are on an active trip or online, depending on the platform.
• They do not know about the other apps you ran at the same time.
• They do not show total miles on the car, which you need for the business-use percentage.
• For 2026, you need to separate miles before and after July 1, because the business standard mileage rate went from 72.5 cents to 76 cents under Announcement 2026-11.

Use a mileage tracking app or a paper log for the full picture, and keep the platform summaries as backup. Our rideshare and delivery guides cover the platform side.

If your records were destroyed

Treas. Reg. 1.274-5T(c)(5) says that if you can show your records were lost through circumstances beyond your control, such as fire, flood, earthquake, or other casualty, you have the right to substantiate by reasonable reconstruction. That is a narrow exception. Losing track of a notebook or a phone is unlikely to fit that description.

The return asks about it

The vehicle questions on Schedule C, Part IV, and Form 4562, Part V, ask for total, business, and commuting miles, and whether you have evidence to support the business use claimed and whether that evidence is written. Treas. Reg. 1.274-5T(d)(2) is the source of those questions. You sign the return under penalties of perjury, so answer accurately.

Which method needs the log?

Both. The standard mileage rate replaces your receipts for gas, repairs, and insurance. It does not replace the mileage log. Actual expenses need the log and the receipts. See standard mileage vs. actual expenses and, for the bigger audit picture, what the IRS examines in a Schedule C audit.