Short answer
For each business trip the IRS expects the date, the destination, the business purpose and the miles driven, plus your total miles for the year. The record should be made at or near the time of the trip, in a log, diary, spreadsheet or app.
What must each trip entry contain?
Publication 463 lists the elements you must be able to prove for the business use of a car:
| Element | What to write | Example |
|---|---|---|
| Date | The day of the trip | March 4, 2026 |
| Place | Where you went (name or address) | Client office, 410 Congress Ave |
| Business purpose | Why the trip was for business | Kitchen remodel estimate |
| Amount | Miles driven for the trip | 18.4 mi |
For the year you also need the total miles driven, all uses together. Schedule C asks for both, which is why it pays to keep personal and commuting trips in the same record.
To start one today, download our free mileage log template: Excel, CSV or printable PDF.
What does "at or near the time" mean?
The IRS gives more weight to a record made when the trip happened than to a statement written months later. A log filled in the same day or the same week is the norm. A record rebuilt at the end of the year from memory alone is weak; one rebuilt from data recorded at the time, like GPS history, calendar entries or receipts, stands on firmer ground. Our guide to the forgot to track mileage for taxes goes through that case.
Which trips count as business, and which do not?
- Business: driving to a client, a job site, a supplier, between two work locations, or to a temporary work location.
- Commuting: driving between your home and your regular place of work. It is personal and not deductible, even if you work during the drive.
- Personal: everything else.
If your home is your principal place of business, trips from home to other work locations are generally business, not commuting. The rules have nuances: Publication 463 has the full table, and your tax professional can apply it to your case.
Which numbers go on Schedule C?
If you claim car expenses as a sole proprietor and are not filing Form 4562, Part IV of Schedule C asks for the miles you drove in the year, split three ways: line 44a business, line 44b commuting, line 44c other. It then asks whether you have evidence to support the deduction, and whether that evidence is written. A complete log answers yes to both.
What makes a log easy to defend?
- Every trip appears, not only the business ones, so the totals add up.
- The purpose is specific: "estimate for the Garcia remodel", not "business".
- The miles match the route, and the yearly total matches your odometer or service records.
- The log is kept with the rest of your records for the full period the return can be examined.
Common questions
Does a mileage log have to be on paper?
No. Publication 463 accepts an account book, a diary, a log, a trip sheet or a similar record, and electronic records count. What matters is the content and that it was made at or near the time.
Do I need odometer readings?
The IRS asks for the miles of each business trip and your total miles for the year. Odometer readings at the start and end of the year are a common way to prove the total, and Schedule C asks for your total miles, but per-trip odometer readings are not required.
How long should I keep my mileage log?
Keep it as long as the return it supports can be examined: generally three years from the date you filed, longer in some cases described in Publication 583.
Can I log only part of the year?
Publication 463 allows a record covering a representative part of the year when it shows a pattern that holds for the whole year, for example one week each month. You must be able to show the sample is representative.