How to Calculate Business Use Percentage for Vehicle Deductions

To calculate the business use percentage for vehicle deductions, divide the miles you drove for business during the year by the total miles you drove that year, then multiply by 100. If you put 12,000 miles on the car and 8,000 of them were business, your business use percentage is 66.7 percent, and roughly two-thirds of your vehicle costs become deductible. That single ratio drives everything else on the return: the size of your deduction, whether you qualify for accelerated depreciation, and whether the IRS will let the deduction stand at all.

The Formula

Record your odometer on January 1 and again on December 31. The difference is your total annual mileage. Tally every mile driven for business during the year. Divide business miles by total miles, then multiply by 100.¹

A quick example. Suppose the car logged 15,000 miles for the year and 9,000 were business. That’s a 60 percent business use rate. If your total vehicle expenses came to $8,000, you can deduct $4,800. Drop the business miles to 3,000 out of the same 15,000 and the percentage falls to 20 percent, cutting the deduction to $1,600. The formula never changes; the percentage swings with how carefully you separate business from personal driving.

If you bought the vehicle or first used it for business partway through the year, measure from the date you placed it in service rather than January 1. Total mileage runs from that start date through December 31, and business miles are the qualifying trips within that shorter window.

Which Miles Count as Business

Business miles include travel between work locations, trips to meet clients or customers, drives to pick up supplies, and any other travel directly tied to earning income. Leaving your office to visit a job site across town counts as a round trip. Driving from one client meeting to another counts too.²

Commuting Doesn’t Count

Miles between your home and your regular workplace are commuting, and commuting is personal no matter how far you drive or what you do along the way.³ Taking business calls from the car doesn’t convert a commute into a business trip. This is the most common mistake in mileage logs and the first thing an auditor will look for.

The Home Office Exception

If your home office qualifies as your principal place of business, the rule flips. Driving from that home office to a client site or another work location counts as deductible business travel rather than commuting.² The exception can push your business use percentage substantially higher, but only if the home office genuinely meets the IRS test for a principal place of business.

Temporary Work Locations

Travel to a temporary work location is deductible even when you also have a regular office. The catch is duration: the assignment must realistically be expected to last one year or less. Once expected duration crosses that line, the location stops being temporary and travel to it becomes nondeductible commuting. The IRS looks at your realistic expectation at the time, not whether the calendar has actually rolled past 12 months.²

Advertising on the Vehicle

Wrapping your car in logos does not turn personal driving into business miles. The IRS has said so directly: display material on the vehicle doesn’t change its use.² A commute in a branded truck is still a commute.

What You Multiply the Percentage By

Once the percentage is set, you apply it through one of two methods.

Standard Mileage Rate

For 2026, the IRS rate is 72.5 cents per business mile.⁴ Multiply the rate by your business miles. Ten thousand business miles produces a $7,250 deduction. The rate already accounts for gas, oil, repairs, insurance, registration, and depreciation, so those costs don’t get deducted separately. Business-related parking and tolls are deductible on top of it.⁵

One timing rule trips people up. To use the standard mileage rate at all, you must choose it in the first year you use the vehicle for business. Claim actual expenses that first year and the standard rate is off the table for that vehicle permanently. In later years you can switch between methods, but only if you started with the standard rate. For a leased vehicle, choosing the standard rate locks you in for the entire lease, including renewals.⁴

Actual Expense Method

Here you track every vehicle cost for the year and multiply the total by your business use percentage. Deductible costs include gas, oil, repairs, tires, insurance, registration, licenses, and depreciation (or lease payments).⁵ Annual expenses of $10,000 at a 70 percent business use rate produce a $7,000 deduction. This method often wins on expensive vehicles or ones with heavy maintenance costs, but the recordkeeping load is much heavier.

The Five-Vehicle Rule

If you own or lease five or more vehicles used for business simultaneously, the standard mileage rate is unavailable for any of them. You must use the actual expense method across the fleet and calculate business use separately for each vehicle.²

Why the 50 Percent Line Matters

The percentage does more than scale your deduction. It decides whether the most valuable depreciation options are open to you at all. A vehicle is “listed property” under the tax code, and listed property has to be used more than 50 percent for business to qualify for Section 179 expensing or bonus depreciation.⁶

Business use at 50 percent or less in the year you place the vehicle in service limits you to straight-line depreciation over a longer recovery period. That’s a real cut to your early-year deductions.

The risk continues past year one. If you took accelerated depreciation or a Section 179 deduction based on business use above 50 percent, and your percentage later drops to 50 percent or below, you have to recapture the excess. The difference between what you actually deducted and what you would have deducted using straight-line gets added back to income in the year the drop happens.⁶ Recapture can create an unexpected tax bill years after the purchase, which is why checking the percentage each year is worth the effort.

Records That Hold Up in an Audit

None of this survives without documentation. Federal law disallows the deduction outright if you can’t substantiate the amount, time, place, and business purpose of each expense.⁷ For a vehicle deduction, that means recording the business mileage, timing, and purpose of each trip.⁸

Each trip entry should show the date, the starting and ending odometer readings (or total miles), the destination, and the business purpose, phrased specifically enough that someone reading it later can tell why the trip was business (for example, “met with client about project proposal”).

Records must be created at or near the time of the trip. Rebuilding a year of mileage from memory in April is the kind of evidence auditors throw out. Digital mileage apps work well and often beat handwritten logs because they timestamp entries as they go.

The Sampling Shortcut

You don’t necessarily have to log every trip for all 12 months. The IRS allows detailed records for a representative portion of the year, used to establish the percentage for the whole year. You still need other evidence, such as gas receipts or invoices, showing that your driving pattern held steady through the months you didn’t log in detail.² The shortcut works when business driving is steady. It doesn’t work when the work is seasonal or the driving pattern shifts, because the sample stops being representative.

What It Costs to Get It Wrong

If the IRS disallows the deduction, you owe the unpaid tax plus interest. An accuracy-related penalty adds 20 percent of the underpayment when the error results from negligence or careless disregard of the rules.⁹ If the underpayment is due to fraud, the penalty jumps to 75 percent of the fraudulent portion.¹⁰ Keep the records at least three years after filing, the standard IRS audit window for most returns.¹¹

Where the Percentage Goes on Your Return

Self-employed filers report vehicle information in Part IV of Schedule C if they’re claiming the standard mileage rate, leasing the vehicle, or using a fully depreciated vehicle and don’t otherwise need Form 4562. That section asks for total miles, business miles, commuting miles, and other personal miles.¹² If you’re claiming depreciation on the vehicle, or need Form 4562 for any other reason, report vehicle use in Part V of Form 4562 instead.¹³ Using more than one vehicle for business means attaching a separate statement with the same information for each additional vehicle.

1
Internal Revenue Service. Instructions for Form 2106 (2025)
2
Internal Revenue Service. Publication 463, Travel, Gift, and Car Expenses
3
eCFR. 26 CFR 1.162-2 – Traveling Expenses
4
Internal Revenue Service. IRS Sets 2026 Business Standard Mileage Rate at 72.5 Cents Per Mile, Up 2.5 Cents
5
Internal Revenue Service. Topic No. 510, Business Use of Car
6
Office of the Law Revision Counsel. 26 USC 280F – Limitation on Depreciation for Luxury Automobiles
7
Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses
8
eCFR. 26 CFR 1.274-5 – Substantiation Requirements
9
Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
10
Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty
11
Internal Revenue Service. How Long Should I Keep Records
12
Internal Revenue Service. Schedule C (Form 1040) – Profit or Loss From Business
13
Internal Revenue Service. Instructions for Schedule C (Form 1040)