If you deduct business mileage or request reimbursement, the IRS expects clear, contemporaneous records. A solid mileage log protects deductions, makes reimbursements non‑taxable, and reduces audit risk.
This guide summarizes what the IRS expects and how to keep records that stand up to scrutiny.
What the IRS requires in a mileage log
The IRS requires adequate records that show the amount, time, place, and business purpose of each trip. These records should be made at or near the time of the expense and kept in a consistent log (paper, spreadsheet, or app).
At a minimum, record:
- Date of the trip
- Start and end location
- Odometer readings (or total miles)
- Business purpose of the trip
- Whether the trip was business or personal
Keep your log up to date
The IRS trusts logs made at the time of the trip. A mileage log you update regularly (daily or weekly) is much stronger than a log rebuilt months later from memory.
Receipts and supporting documents
Mileage logs are the core record, but you should also keep supporting evidence such as calendars, client emails, invoices, or job tickets that show the business purpose and timing of trips. The IRS allows reasonable methods of substantiation, but your records must be specific and consistent.
Common audit issues (and how to avoid them)
- Commuting counted as business mileage: Regular travel between home and your main workplace is commuting, not deductible business mileage.
- Missing purpose: Logs that list only miles without a business reason can be disallowed.
- Inconsistent totals: Large differences between logs, calendar entries, and reported mileage raise questions.
- Reconstructed logs: Backfilled logs are less credible than contemporaneous records.
Practical tips to stay compliant
- Log trips the same day you drive
- Note the business purpose in plain language
- Keep a simple backup trail (calendar, emails, invoices)
- Separate commuting from business miles
- Store your log for at least the tax recordkeeping period
If you want to see how mileage reimbursement is calculated or which rate to use, read our IRS Mileage Reimbursement Guide and Mileage Tracking Guide.
