Car loan interest is tax-deductible only if you use the vehicle for business, and the deduction equals the business-use percentage of the total interest you paid during the tax year. For example, if you paid $1,200 in interest and used the car 60% for business, you can deduct $720. The IRS does not allow deductions for personal-use vehicles, but if you’re self-employed, a small-business owner, or an employee who drives for work (and is not reimbursed), you may qualify. The key is separating business miles from personal miles and applying the correct percentage to your total interest. This article explains how to calculate the deduction, what records you need, and how to use the Car Loan Calculator to estimate your total interest in seconds.
When Car Loan Interest Is Tax-Deductible
The IRS allows a car loan interest deduction only if the vehicle is used for business. Personal use—commuting to a regular job, running errands, or family trips—does not qualify. If you’re self-employed, a freelancer, or a small-business owner, you can deduct interest if you use the car for business purposes like client meetings, deliveries, or travel between job sites. Employees who are not reimbursed for work-related driving may also qualify, but the rules are stricter and require itemizing deductions, which fewer taxpayers do since the 2017 tax law changes.
To claim the deduction, you must own the car (not lease it) and have a loan secured by the vehicle. The deduction is calculated as a percentage of the total interest paid during the tax year, based on the percentage of miles driven for business. For example, if you drove 10,000 miles total and 6,000 were for business, your business-use percentage is 60%. If you paid $1,200 in interest, you can deduct $720.
How to Calculate Your Business-Use Percentage
Your business-use percentage is the ratio of business miles to total miles driven during the tax year. The IRS requires a contemporaneous mileage log—meaning you record each trip’s date, purpose, starting and ending odometer readings, and total miles. You can use a notebook, spreadsheet, or a mileage-tracking app. At the end of the year, add up all business miles and divide by total miles to get your percentage.
For example:
| Category | Miles Driven |
|---|---|
| Business miles | 6,000 |
| Personal miles | 4,000 |
| Total miles | 10,000 |
Business-use percentage = 6,000 ÷ 10,000 = 60%.
If you use the car for both business and personal trips, you must track every mile. The IRS does not accept estimates or round numbers—your log must be detailed and accurate.
Estimate Total Interest Paid with the Car Loan Calculator
To calculate your deduction, you need to know the total interest you paid during the tax year. Your lender may send a Form 1098 showing mortgage interest, but car loans rarely come with this form. Instead, you can estimate your total interest using the Car Loan Calculator. Here’s how it works:
- Enter the vehicle price, your down payment, and any trade-in value.
- Type in the annual percentage rate (APR) your lender offers and select a loan term (36 to 84 months).
- The calculator instantly shows your estimated monthly payment, total interest, and total cost of the loan.
For example, if you financed $25,000 at 5% APR for 60 months, the calculator estimates you’ll pay about $3,300 in total interest. If your business-use percentage is 60%, your deduction would be $1,980.
The calculator is free, private, and works in your browser—no sign-up or personal data required. It’s faster than building a spreadsheet or using a formula, and it gives you a clear picture of your total interest before you file your taxes.
How to Claim the Deduction on Your Tax Return
If you’re self-employed, report the deduction on Schedule C (Form 1040), line 9, labeled “Car and truck expenses.” You’ll enter the business-use percentage of your total interest here. If you’re an employee claiming unreimbursed business expenses (rare since 2018), you’d use Form 2106, but most taxpayers no longer qualify for this deduction.
Keep your mileage log and loan documents for at least three years after filing. The IRS can audit you and ask for proof of business use. If you can’t provide records, they may disallow the deduction and charge penalties.
For more details on IRS rules, see the IRS Topic No. 510: Business Use of Car page.
Compare Your Deduction to Standard Mileage Rate
The IRS offers two ways to deduct car expenses: actual expenses (including interest) or the standard mileage rate. In 2026, the standard mileage rate is 67 cents per business mile. You can choose whichever method gives you a larger deduction, but you must use the same method for the entire year.
For example, if you drove 6,000 business miles, the standard mileage deduction would be $4,020 (6,000 × $0.67). If your actual expenses (including interest) total less than this, the standard mileage rate is better. The Car Loan Calculator helps you estimate your interest, but you’ll need to add other expenses (gas, insurance, maintenance) to compare.
| Method | What’s Included | Best For |
|---|---|---|
| Actual expenses | Interest, gas, insurance, repairs, depreciation | High-mileage drivers with expensive cars |
| Standard mileage rate | 67 cents per business mile (2026) | Low-mileage drivers or those who don’t track expenses |
Most small-business owners with newer cars benefit from actual expenses, while those with older cars or fewer miles often prefer the standard rate. Use the Home Affordability Calculator to see how deductions affect your overall tax picture.
Pitfalls to Watch For
- Deducting interest for personal use: Only business miles count. Commuting to a regular job is personal use.
- Not keeping a mileage log: The IRS requires contemporaneous records. Estimates or guesses won’t hold up in an audit.
- Mixing business and personal trips: If you stop for personal errands on a business trip, only the business portion counts.
- Forgetting to prorate interest: If you sold the car or paid off the loan mid-year, you can only deduct interest for the months you owned it.
- Claiming the deduction as an employee: Since 2018, unreimbursed employee expenses are no longer deductible for most taxpayers.
If you’re unsure whether you qualify, consult a tax professional or use the Retirement Calculator to see how deductions affect your long-term savings.
See also: Calculate Car Loan Interest in Seconds Without Spreadsheets.
For a deeper look, see How to Calculate Compound Interest for a Loan.
For a deeper look, see Calculate Discount Percentage in Excel and Beyond.