Your mileage deduction needs two numbers most drivers never write down.

Why business miles aren't enough

Most drivers think of the mileage deduction as one number: business miles times the IRS rate. But IRS Publication 463 lists what you need to prove a car expense, and two mileage figures appear side by side: the miles for each business use and the total miles for the year.

Schedule C asks for the same thing. If you take the standard mileage rate, Part IV asks when you started using the car for business, then has you take your year's total miles and enter how many were:

• business (driving for Uber, Lyft, DoorDash, Instacart and so on)
• commuting
• other (everything personal)

The three have to add up to the total, and the total comes from the odometer. The same part of the form asks whether you have evidence to support the deduction and whether that evidence is written. You want to be able to answer yes to both.

Why the total matters

Your total miles are the check on your business miles. Business divided by total gives your business-use percentage. If you claim 21,000 business miles on a car that only went 19,000 miles that year, something is wrong, and the odometer is how anyone, including an examiner, would find that out.

The percentage matters even more if you use actual expenses instead of the standard rate. Then it decides how much of your gas, insurance, repairs and depreciation you can deduct. Publication 463's own example: 12,000 business miles out of 20,000 total means you can deduct 60% of the car's costs.

Why "about 20,000" doesn't work

For most business expenses, if you can show you spent money but not exactly how much, the Tax Court can sometimes estimate it for you. Cars are an exception. Section 274(d) of the tax code puts vehicles in a stricter group that needs specific records, and since Sanford v. Commissioner (1968) the Tax Court has held that it can't estimate those expenses for you.

In practice that means a deduction without records can be disallowed entirely, not trimmed. Publication 463 says records should be made at or near the time, and that a record kept at the time is worth more than one put together later from memory. A log rebuilt from memory at tax time is exactly the kind of record that loses.

A worked example

A driver works Uber and DoorDash in a 2021 Camry. Their records for the year look like this:

Business use is 80% (18,000 ÷ 22,500). Every line on the form has a source: two dated readings for the total and a trip-by-trip log for the business share. Without the readings, the 22,500 and the 4,500 are guesses, and the 18,000 has nothing to be checked against.

What a good odometer record looks like

The IRS doesn't set a format, but a reading should show the date, the number and which car it's for. A photo of the dashboard, with the date it was taken, is the easiest version to make and the hardest to argue with.

Take a reading:

• on January 1 and December 31 (the first is also the start of next year)
• the day you start using a car for business, if that's partway through the year
• when you buy, sell or trade in a car. Each car needs its own start and end.
• at the start and end of a shift, if you want extra proof. It's optional, but it fences in that shift's business miles on its own.

Paperwork that backs up your readings

You probably already have dated odometer readings you never think about. Keep them with your tax records:

• oil change and repair invoices, which usually print the mileage
• state inspection or emissions reports
• purchase, sale and trade-in paperwork
• rental or lease return forms

None of these replaces a trip log, but they make your readings believable and can fill a gap.

If you missed January 1

Take a reading today and date it. Then look for the paperwork closest to January 1, such as an oil change in early January or a December inspection, and keep it with your records along with a note of how you worked out the year's starting figure. That's weaker than a reading taken on the day, so set a reminder for this December 31 so next year starts clean.

How long to keep it

Publication 463 says to keep the records behind a deduction for at least 3 years from the date you file the return that claims it. If you're depreciating the car under actual expenses, keep its records for as long as you're depreciating it. Photos and PDFs are fine. What matters is that you can still find them.

Quick answers

Do I need odometer readings if I use the standard mileage rate?

Yes. The rate replaces receipts for gas and repairs, but Schedule C still asks for your total miles and how they split. Your total miles come from the odometer.

Does the IRS require a photo of the odometer?

No. A dated written reading is a record. A photo is simply better evidence, because it's hard to fake and records the date by itself.

Is my Uber or DoorDash tax summary enough?

No. It covers only the miles that app saw, and it says nothing about your car's total miles. If you run more than one app, the summaries can also count the same mile twice.

I use two cars. One reading or two?

Two sets: a start and end reading for each car, and each trip logged against the car you drove.

Sources

• IRS Publication 463: Travel, Gift, and Car Expenses (chapter 5, Recordkeeping, and Table 5-1)
• IRS: Instructions for Schedule C (line 9, and Part IV, Information on Your Vehicle)
• IRS: Schedule C (Form 1040)
• 26 U.S.C. § 274(d): substantiation required
• Sanford v. Commissioner, 50 T.C. 823 (1968), aff'd per curiam, 412 F.2d 201 (2d Cir. 1969)

This article is general information, not tax advice. Your situation may differ, so check with a tax professional before you file.