What does a business mileage log need to show?

The elements to record

Table 5-1 in Publication 463 (2025) breaks the proof into elements. For transportation, you need the cost of each separate expense; for car expenses specifically, the cost of the car and any improvements, the date you started using it for business, the mileage for each business use, and the total miles for the year. You need the date of each expense or use, your business destination, and the business purpose. The sample Table 5-2, a daily business mileage and expense log, has columns for date, destination (city, town or area), business purpose, odometer start and stop, miles this trip, and the type and amount of other expenses such as gas, oil and tolls, with weekly and year-to-date totals.

Estimates do not count

The publication is blunt: you cannot deduct amounts that you approximate or estimate. You should keep adequate records to prove your expenses or have sufficient evidence to support your own statement. A written record is generally needed because written evidence is more reliable than oral evidence alone, and a record prepared on a computer is considered adequate, so a spreadsheet or a mileage app qualifies if it captures the elements and you can produce it.

Timely means near the time

You should record the elements at or near the time of the expense or use. You do not need to write down every trip the same day. If you keep a log on a weekly basis that accounts for use during the week, it is considered timely. A record put together months later, from memory, is weak because of the lack of accurate recall. If you give your employer or client an expense statement that you copied from your log or diary, that can also be a timely record.

Business purpose and routine routes

You generally must give a written statement of business purpose, but the degree of proof depends on the circumstances, and if the purpose is clear from the surrounding circumstances you do not need to explain. The publication’s example is a sales representative who calls on customers along an established route: it is enough to record the length of the route once, the date of each trip at or near the time, and the total miles driven during the year. Minimal personal use, such as a stop for lunch between two business stops, does not interrupt business use, and a round trip or uninterrupted business use can be one record.

Sampling, and when you lose records

You may keep an adequate record for part of the year and use it to prove the business share for the whole year, if you can show by other evidence that the sample period is representative. The publication’s example is a person who keeps records during the first week of each month showing 75% business use, and invoices that show the use continues at the same rate in later weeks. If records are lost to fire, flood or other casualties beyond your control, you can reconstruct them. If you only have incomplete records, you can combine your own written or oral statement with other supporting evidence.

Receipts, and the $75 rule

You generally need documentary evidence such as receipts, canceled checks or bills. It is not needed if the expense, other than lodging, is less than $75; if you have a transportation expense for which a receipt is not readily available; or if you account to your employer under an accountable plan using a per diem that includes meals or lodging. Adequate evidence shows the amount, date, place and essential character of the expense. A canceled check alone does not prove a business purpose. Those exceptions waive the receipt, not the log: you still record the elements. See the parking and tolls page for the expenses people most often leave out.

How long to keep them

Keep records for as long as they may be needed to administer any provision of the Internal Revenue Code, which generally means 3 years from the date you file the return on which the deduction is claimed. A return filed early is treated as filed on the due date. Keep records of the business use of your car for each year of the depreciation recovery period. Employees who give records to their employers and are reimbursed generally need not keep copies, unless they claim expenses above reimbursements, are paid under a nonaccountable plan, or are related to the employer.

Worked example

Your log shows 9,450 business miles and the odometer shows 14,000 miles for the year. Business use is 9,450 divided by 14,000, which is 67.5%. At the 2025 standard mileage rate of $0.70, the deduction is $6,615. If you use actual expenses, 67.5% of your car costs is the business share. Rates for other years are on the rate history page, and the gas page compares the two methods.

Sources

• IRS Publication 463, Travel, Gift, and Car Expenses (2025): Chapter 5, How To Prove Expenses; What Are Adequate Records?; Documentary evidence; Timely kept records; Proving business purpose; Sampling; Destroyed records; Car expenses; How Long To Keep Records and Receipts; Table 5-1; Table 5-2. Read November 2, 2026.

Edition read: Publication 463 (2025), for use in preparing 2025 returns. Rates and dollar limits on this page are the 2025 figures printed in that edition; check the current publication, form instructions and GSA.gov per diem tables for your tax year. This page summarizes the publication and does not replace it.