Supporting Vehicle Expenses in an IRS Audit: How to Use a 90-Day Sample
When it comes to deducting vehicle expenses, everyone loves to reference the 6,000-pound rule — the guideline that allows heavier vehicles to potentially deduct more under Section 179. However, few business owners know how to shortcut documentation for vehicle mileage in case of an IRS audit.
At Velin & Associates, Inc., we help business owners, freelancers, and creators — from YouTubers and TikTokers to doctors, dentists, and Shopify store owners — understand how to maximize vehicle-related tax deductions while staying fully compliant.
This guide explains how you can use IRS regulations to support vehicle expenses even if you don’t have a full year’s mileage log.
IRS Best Practices for Vehicle Deductions
The IRS generally expects you to maintain a mileage log for all business trips. Your log should include:
- Date of the trip
- Purpose of the trip
- Starting point and destination
- Business miles driven
Maintaining a full-year mileage log ensures you can substantiate deductions for both the standard mileage rate and actual vehicle expenses.
But what if you don’t have a complete log? The IRS provides guidance that can help you support your deduction without starting from scratch.
The 90-Day Sample Method
According to Treasury Regulation §1.274-5T(c)(3)(ii)(A), taxpayers may substantiate annual business mileage using a 90-day sample period, provided the sample is representative of typical business use.
Key Points of the Regulation:
- Representative Sample – The 90-day mileage log must reflect your average daily business use.
- Extrapolation – You can multiply the sample by the number of days in the year to estimate total business miles.
- Documentation – Keep detailed records for the 90-day period, including mileage, purpose of trips, and destinations.
This method is especially useful if you forgot to maintain a full-year log but can provide credible evidence of business use.
Example Scenarios:
- Freelancers & Creators
- A YouTuber traveling to shoots for three months can use that period to estimate total annual mileage. If the 90-day sample shows 3,000 business miles, you can reasonably extrapolate 12,000 miles for the year.
- Medical Professionals
- A dentist making regular visits to patient homes or satellite clinics can use a 90-day sample to support business miles driven, even if prior months were not logged.
- Online Commerce & Retail Business Owners
- A Shopify store owner delivering products locally can show a representative 90-day period of trips to clients or suppliers to substantiate vehicle deductions.
Why This Matters for an Audit
Many business owners fear that missing mileage logs will trigger IRS disallowance. Using the 90-day sample method under §1.274-5T(c)(3)(ii)(A) gives you a strong, regulation-backed way to support deductions.
Best practice tips:
- Keep the 90-day period well-documented and representative of normal business activity.
- Include receipts, calendar entries, or digital logs to reinforce your sample.
- Combine with other vehicle expense records (fuel, maintenance, insurance) to strengthen your audit position.
Common Mistakes to Avoid
- Using a 90-day period that is not typical (e.g., unusually high travel month).
- Relying solely on estimates without supporting records.
- Mixing personal and business mileage without a clear method for allocation.
How Velin & Associates, Inc. Can Help
At Velin & Associates, Inc., we help high net worth individuals, business owners, and creators navigate IRS regulations, including vehicle deductions and audit support. We can:
- Set up a compliant mileage tracking system for future tax years.
- Calculate deductions using 90-day samples that meet IRS requirements.
- Review past mileage records to maximize your deduction while minimizing risk.
- Advise Shopify store owners, Amazon sellers, YouTubers, TikTokers, doctors, dentists, and online creators on proper documentation for IRS compliance.
Final Thoughts
Missing a full-year mileage log doesn’t have to mean losing your vehicle deduction. By using a 90-day representative sample, backed by Treasury Regulation §1.274-5T(c)(3)(ii)(A), you can present a credible, IRS-compliant estimate.
Proper preparation is key. The IRS rewards good-faith documentation and reasonable estimates.
For more information about our tax planning services, contact us today: visit our website.
Velin & Associates, Inc
8159 Santa Monica Blvd STE 198/200 West Hollywood, CA 90046
323-902-1000
dmitriy@losangelescpa.org
Our firm provides the information in this e-newsletter for general guidance only, and does not constitute the provision of legal advice, tax advice, accounting services, investment advice, or professional consulting of any kind. The information provided herein should not be used as a substitute for consultation with professional tax, accounting, legal, or other competent advisers. Before making any decision or taking any action, you should consult a professional adviser who has been provided with all pertinent facts relevant to your particular situation. Tax articles in this e-newsletter are not intended to be used, and cannot be used by any taxpayer, for the purpose of avoiding accuracy-related penalties that may be imposed on the taxpayer. The information is provided "as is," with no assurance or guarantee of completeness, accuracy, or timeliness of the information, and without warranty of any kind, express or implied, including but not limited to warranties of performance, merchantability, and fitness for a particular purpose.