Vehicle mileage audit: building records for a car deduction

What the exam is about

Vehicle deductions are tested because personal and business driving mix easily. A letter may ask for the number of miles driven for business, the total miles for the year, and support for each. The examiner is trying to confirm that the business portion is real and is documented.

Before you gather anything, read the request closely for the tax year, the vehicle or vehicles named, and whether the examiner is asking about mileage, actual costs or both. Answer what was asked. If two vehicles are involved, or one was replaced during the year, keep their records in separate folders so the totals never blur together.

What the IRS says about records

IRS Publication 463 says that when you travel away from home on business you must keep records of your expenses, and that a log, diary, notebook or other written record can be used. The part of the publication read for this page did not cover every rule on car records, so open the current edition and read the section on adequate records.

The publication states a standard mileage rate for business use of a car, but the rate changes each year. Use the rate for the tax year under audit and check the current IRS page instead of relying on a number from an old return.

A practical way to use that guidance is to treat the log as the backbone and everything else as corroboration. Receipts for fuel or repairs do not by themselves show where you drove or why, while a calendar entry or client invoice can show that a trip happened on a particular day. Each type of record answers a different question, so together they tell a more complete story than any one alone.

Example: a home health aide with a client route

Consider an independent home health aide who drives to several clients each week. Her best record is a running log with the date, starting point, destination, business reason and miles. If she did not keep one, she can rebuild it from her appointment calendar, client billing records and map history, and label it clearly as a reconstruction made later.

Compare that to a sales representative who works a territory. His calendar, customer visit reports and expense reports may already show most of what is needed; his task is to line them up trip by trip.

Building or rebuilding a log

A good log is plain, consistent and tied to other evidence.

When you reconstruct, work from the strongest evidence outward. Start with dated documents you did not create yourself, such as client invoices, delivery records or appointment confirmations, then add map directions for each destination, then fill in the remaining trips from your calendar. Add a short cover note explaining what sources you used and when you prepared the log, so the examiner can see the method rather than guess at it.

• Date, destination and business purpose for each trip
• Odometer readings at the start and end of the year, if you have them
• Calendars, invoices or client records that match the trips
• A note on how you separate commuting and personal use

Mistakes to avoid

Do not round every trip to the same number of miles. Do not claim all driving as business if you also use the car personally. Do not present a log as written at the time if you built it later; label it honestly, because the examiner will compare it with other records.

If you used actual expenses instead of the mileage rate, you will also need receipts for fuel, repairs and insurance, and a way to allocate business use.

Two more problems come up often. A log with a long run of entries in identical handwriting and ink can look manufactured, so type a clean reconstruction instead and say it is one. And a log that covers only the trips that helped the deduction, while leaving out ordinary personal driving, makes totals hard to trust; show the total miles for the year and how you arrived at the business share.

Who can help and how to respond

If vehicle use is a major part of your business, a practitioner can help you decide which method fits. For a straightforward request, you can respond yourself. IRS Audit Defense Pro is software that helps you organize your facts and draft a response letter you review and send yourself; it is not a law firm, CPA or enrolled agent. For this topic, a cover letter that explains your method and attaches the log is a clean way to present it.

Frequently asked questions

Sources

• IRS Publication 463: Travel, Gift, and Car Expenses
• IRS Publication 583: Starting a Business and Keeping Records

Related guides

• Schedule C audit: supporting your business income and expensesA Schedule C audit tests the income and expenses of your sole proprietorship.
• Home office deduction audit: proving the space qualifiesIn a home office exam the IRS wants to see that part of your home is used regularly and exclusively for business, and how you figured the deduction.
• Hobby loss audit: is your activity a business or a hobby?In a hobby loss exam the IRS asks whether an activity is carried on for profit.
• Correspondence audit: how an IRS audit by mail worksA correspondence audit is an IRS audit handled entirely by mail.
• Cover letter for answering an IRS audit document requestAn audit response cover letter references the IRS's request, answers each numbered item in order, lists the photocopies you are sending, asks the examiner to confirm receipt, and gives a contact.
• IRS field audit: what happens when the auditor comes to youA field audit is an in-person IRS examination held at your home, your business, or your representative's office.