Business-Use Percentage: How to Split Your Car Between Business and Personal (2026)

Q: What is business-use percentage for a car?

Business-use percentage is the share of your vehicle's total annual miles that you drove for business, and it's the number that determines how much of your car's costs you can deduct. The formula is simple: business miles divided by total miles driven for the year. If you drove 24,000 miles total and 9,000 of them were for business, your business-use percentage is 37.5%. That percentage then gets applied to your actual car expenses — gas, insurance, repairs, depreciation, registration — to figure the deductible portion, or it determines how much depreciation and Section 179 you can claim on the vehicle. Commuting miles between home and a regular workplace don't count as business miles, and personal errands never do. The percentage is recalculated every year because your driving mix changes.

Q: How do I calculate the business-use percentage of my vehicle?

Take your business miles for the year and divide by your total miles for the year, then multiply by 100. You get business miles from a mileage log — a record of each business trip's date, destination, purpose, and distance. You get total miles from your odometer: reading at the start of the year subtracted from the reading at the end. So if your odometer went from 40,000 to 64,000 (24,000 total miles) and your log shows 9,000 business miles, your business-use percentage is 9,000 ÷ 24,000 = 37.5%. That's the percentage you apply to actual vehicle costs. The two inputs the IRS wants to see are a contemporaneous business-mileage log and your beginning and ending odometer readings — keep both and the calculation is airtight.

Q: Does business-use percentage matter if I use the standard mileage rate?

Not for the deduction itself, but you still need the numbers behind it. With the standard mileage method you deduct a flat rate per business mile — $0.725 for 2026 — so you multiply business miles by the rate and never explicitly compute a percentage or add up actual car costs. However, you still must track your business miles and your total miles, because the IRS wants to see that your claimed business miles are reasonable relative to total driving, and because you may want to compare methods. Business-use percentage becomes essential when you use the actual-expense method, when you depreciate the vehicle, or when you claim Section 179 or bonus depreciation — all of which require applying the percentage to real dollar costs.

Q: What happens if my vehicle's business use drops below 50%?

Falling under 50% business use has real consequences if you took accelerated write-offs. If you claimed Section 179 expensing or bonus depreciation on the vehicle in an earlier year and your business use later drops to 50% or below, you may have to recapture — add back to income — part of those deductions, because the accelerated benefit assumed predominant business use. Going forward, once business use is 50% or less you also can't use Section 179 or accelerated (MACRS) depreciation; you're limited to the slower straight-line method for the business portion. Below 50% business use, many freelancers find the standard mileage rate simpler and often better. The takeaway: business use above 50% preserves your best depreciation options, and dropping below it can trigger recapture, so track the percentage carefully year to year.

Q: Do commuting miles count in business-use percentage?

No. Commuting — driving between your home and a regular place of business — is a personal expense, and those miles count as personal, not business, in the percentage. This is one of the most common ways freelancers overstate business use. The important exception for freelancers: if your home qualifies as your principal place of business, the trip from your home office to a client site or job isn't commuting — it's deductible business travel. So a home-based freelancer often has few or no true commuting miles, while someone with a separate outside office does. Personal errands, family trips, and the daily commute all land in the personal bucket; only genuine business trips go in the numerator of your business-use percentage.

Published: July 18, 2026 · Reading time: 9 min

TL;DR: Your business-use percentage is business miles ÷ total miles for the year — the share of your car's costs you're allowed to deduct. You get business miles from a mileage log and total miles from your odometer (year-end reading minus start-of-year reading). The percentage matters most under the actual-expense method and for depreciation and Section 179. If you use the standard mileage rate ($0.725/mile for 2026), you skip the percentage but still track the miles. And watch the 50% line — dropping below it can trigger depreciation recapture.

Every freelancer who drives for work eventually hits the same question: my car is part business, part personal — how much of it can I actually deduct? The answer is a single number, the business-use percentage, and it drives everything about your vehicle deduction. Get it right and you claim what you're owed with a record that survives an audit. Get it fuzzy and you either leave money on the table or invite trouble. Here's exactly how it works for 2026.

The formula (it's genuinely this simple)

Business-use % = (Business miles ÷ Total miles) × 100

Business miles — every mile driven for a business purpose (client visits, job sites, supply runs, business errands), pulled from your mileage log.
Total miles — every mile the car was driven all year, business and personal, from your odometer: ending reading minus starting reading.

Example: Your odometer went from 40,000 to 64,000 — that's 24,000 total miles. Your log shows 9,000 business miles. Your business-use percentage is 9,000 ÷ 24,000 = 37.5%. If your total actual car costs for the year were $8,000, your deduction under the actual-expense method is 37.5% × $8,000 = $3,000.

That's the whole concept. The work is in the two inputs — and in knowing when the percentage matters.

When business-use percentage actually matters

Here's what trips people up: the percentage is critical for some deduction methods and irrelevant for others.

It matters — a lot — when you use:

The actual-expense method — you multiply gas, insurance, repairs, depreciation, registration, and lease payments by the percentage to get your deduction. See standard mileage vs actual expense.
Depreciation — the percentage limits how much of the vehicle's cost you can write off over time.
Section 179 / bonus depreciation — these accelerated write-offs require more than 50% business use and are applied to the business-use share. See Section 179 and bonus depreciation.

It's behind the scenes when you use:

The standard mileage rate — you deduct a flat $0.725/mile (2026) for business miles and never explicitly compute a percentage or total up actual costs. But you still track business and total miles, because the IRS expects your business share to look reasonable. See the 2026 mileage rate.

So a freelancer using standard mileage multiplies business miles by the rate and is done. A freelancer using actual expenses lives and dies by the percentage.

Getting the two inputs right

Business miles — from a contemporaneous log. For every business trip, record the date, destination, business purpose, and miles. "Contemporaneous" means you log it at or near the time of the trip, not reconstructed months later — reconstructed logs are what auditors discount first. See what the IRS requires for a mileage log and track business mileage IRS requirements.

Total miles — from your odometer. Note the reading at the start of the year (or when you place the car in service) and again at year-end. The difference is total miles. Odometer readings are the denominator the IRS wants to see — read more in odometer readings and your mileage log.

With both in hand, the division is trivial and the number is defensible.

What counts as business — and what doesn't

The fastest way to overstate your percentage is to miscount trips:

✅ Business: driving to a client, a job site, a supplier, a business meeting, or between two work locations.
❌ Personal: errands, family trips, and — importantly — your commute between home and a regular workplace. See commuting vs business miles.

The key freelancer exception: if your home is your principal place of business, the drive from your home office to a client or job isn't commuting — it's deductible business travel. That's the home-office mileage rule, and it's why home-based freelancers often have very few personal commuting miles.

Mixed-purpose trips get split by the business portion. Multi-stop and multi-client days have their own logging approach — see multi-stop, multi-client mileage logs.

The 50% line: why it matters

There's a bright line at 50% business use that every freelancer using actual expenses should watch:

Above 50%: you can use Section 179, bonus depreciation, and accelerated (MACRS) depreciation on the business share.
50% or below: you're limited to slower straight-line depreciation, and you lose Section 179 and bonus depreciation going forward.
Dropping below 50% after claiming accelerated write-offs: you may face depreciation recapture — adding part of those earlier deductions back into income. See depreciation recapture.

If your business use is low and bouncing around the 50% mark, the standard mileage rate is often simpler and avoids the recapture trap entirely. Note that the standard rate has a built-in depreciation component that reduces your basis over time, so it's not free of depreciation math — it just hides it.

One car, or more than one?

Your business-use percentage is per vehicle, recalculated each year because your driving mix shifts. If you run more than one car through the business, track each separately — see multi-vehicle mileage tracking and using two vehicles for business. And if you drive a car you don't own or lease, the rules differ.

Frequently Asked Questions

What is business-use percentage for a car?

It's the share of your vehicle's total annual miles driven for business — business miles ÷ total miles. That percentage determines how much of your car's costs (or depreciation) you can deduct. Commuting and personal miles don't count as business.

How do I calculate the business-use percentage of my vehicle?

Divide business miles (from your mileage log) by total miles (year-end odometer minus start-of-year odometer) and multiply by 100. Example: 9,000 business ÷ 24,000 total = 37.5%.

Does business-use percentage matter if I use the standard mileage rate?

Not for the deduction itself — you deduct $0.725 per business mile and skip the percentage. But you still track business and total miles so the IRS can see your business share is reasonable. The percentage is essential for actual expenses, depreciation, and Section 179.

What happens if my vehicle's business use drops below 50%?

You lose Section 179 and accelerated depreciation going forward (straight-line only), and if you took those write-offs earlier you may have to recapture part of them. Below 50%, the standard mileage rate is often simpler.

Do commuting miles count in business-use percentage?

No — commuting between home and a regular workplace is personal. But if your home is your principal place of business, drives to clients and job sites are deductible business travel, not commuting.

Authoritative References

Let the Percentage Calculate Itself

Business-use percentage is only as good as the miles behind it — and hand-logging every trip is exactly where freelancers slip. CentSense records your business drives automatically at the 2026 rate of $0.725/mile, keeps your total-mileage picture straight, and stores each trip's date, destination, and purpose so your business-use percentage is documented and audit-ready. Start free with 10 AI scans a month — no credit card; the Solo plan ($5/month) adds unlimited scanning and mileage tracking.

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This article is educational and not tax advice. Consult a qualified tax professional about your specific situation.

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