What the Big Beautiful Bill did to car interest deductions

The Tax Cuts and Jobs Act of 2017, often called the "Big Beautiful Bill," eliminated the deduction for interest paid on personal car loans. If you borrowed money to buy a car for personal use — commuting, errands, family trips — you can no longer deduct that interest on your federal tax return. This change took effect in 2018 and remains in place.

However, the rule is different if you use the car for business. If you own a business and borrow money to buy a vehicle used primarily for work, you may still deduct the interest as a business expense. The key word is business use: the car must be used to generate income, not for personal transportation.

This distinction matters because many people use the same vehicle for both purposes. The IRS requires you to track what percentage of your driving is business-related and what percentage is personal. You can only deduct the interest that corresponds to the business portion.

Key Takeaways

  • Personal car loans no longer produce a tax deduction under the 2017 tax law, even if you itemize deductions.
  • Business car loans may still be deductible if the vehicle is used primarily for work and you can document that business use.
  • You must track the percentage of miles driven for business versus personal use to calculate the deductible portion of interest.
  • Self-employed people and business owners should keep mileage logs and loan documents to support any business vehicle interest deduction.

The difference between personal and business vehicle loans

A personal car loan is one where you borrow money to buy a car you drive for everyday life. You use it to get to work, pick up groceries, visit friends, or take vacations. Before 2018, you could deduct the interest on your tax return. That deduction is now gone.

A business car loan is one where you borrow money to buy a vehicle that your business uses to generate revenue. A plumber who finances a work truck, a real estate agent who buys a car for client meetings, or a delivery driver who finances a van are all examples. If the vehicle is used for business, the interest may be deductible.

The IRS does not care what you call the loan. It cares how you use the car. If you drive a financed vehicle 80% for business and 20% for personal errands, only 80% of the interest is deductible. You must keep records to prove those percentages.

How to track business use and calculate your deduction

The IRS expects you to maintain a mileage log that shows the date, destination, business purpose, and miles driven for each trip. You do not need to write down every single trip, but you should record enough trips throughout the year to establish a pattern. Many business owners keep a small notebook in the car or use a mileage tracking app.

At the end of the year, add up your total business miles and divide by your total miles driven (business plus personal). That percentage is what you can deduct. For example, if you drove 12,000 business miles and 3,000 personal miles out of 15,000 total, your business use is 80%. You would deduct 80% of the interest you paid that year.

Keep your loan documents, payment records, and mileage logs together. If the IRS ever questions your deduction, these records are your proof that the vehicle was used for business. Without them, the IRS will disallow the deduction entirely.

Self-employed people and business owners: what changed for you

If you are self-employed or own a business, the 2017 tax law did not eliminate your ability to deduct vehicle interest — it just narrowed it. You can still deduct interest on a business vehicle, but you must prove the business use. This is stricter than before, when some taxpayers could deduct interest more loosely.

The law also changed how you can deduct vehicle expenses overall. You can choose between two methods: the standard mileage rate or actual expense method. Under the standard mileage rate, you deduct a set amount per business mile (the rate changes each year). Under the actual expense method, you deduct a percentage of all your vehicle costs, including interest, insurance, fuel, and repairs. You cannot use both methods in the same year, and switching between them has rules.

If you use the actual expense method, the interest deduction is part of your overall vehicle deduction. If you use the standard mileage rate, you do not deduct interest separately — it is built into the per-mile rate. Choose the method that gives you the larger deduction, but be prepared to document your choice and your business use.

What the law says about mixed-use vehicles

The tax code does not prohibit deducting interest on a vehicle you use for both business and personal purposes. It requires you to deduct only the business portion. This is called apportionment, and it applies to all vehicle expenses, not just interest.

The IRS is strict about this. If you claim 100% business use on a vehicle you clearly drive home at night, you risk an audit. Conversely, if you underestimate your business use, you are leaving money on the table. The safest approach is to keep honest records and deduct what those records support.

Some taxpayers try to avoid this by buying a second vehicle used only for business. That is a valid strategy, but it costs money upfront. Whether it makes sense depends on your situation and how much you drive for business.

Vehicles you cannot deduct interest on, even for business

Certain vehicles have limits on how much you can deduct. Luxury vehicles — generally defined as cars with a basis (purchase price) over a certain amount — are subject to depreciation caps. These caps limit how much of your vehicle cost you can deduct each year, which indirectly limits your interest deduction if you are using the actual expense method.

Vehicles weighing over 6,000 pounds, such as large SUVs and trucks, have different rules and may allow larger deductions. However, the interest deduction itself is not affected by vehicle weight. The weight rule applies mainly to depreciation.

If you use a vehicle for business only part of the time, you can deduct interest only on the business portion, as described above. There is no special exception or workaround.

Frequently Asked Questions

Can I deduct car loan interest if I use the car to drive to my job?

No. Driving to and from work is considered personal use, not business use, even if you work for someone else. The deduction applies only to self-employed people and business owners who use a vehicle to generate income — such as making client visits, deliveries, or sales calls as part of running a business.

What if I have a car loan from before 2018?

The 2017 tax law applies to all car loans, regardless of when you took them out. If your loan is personal use, you cannot deduct the interest, even if you could have before 2018. If your loan is for a business vehicle, you can deduct the business portion of the interest.

Do I need to deduct interest, or can I deduct the whole car payment?

A car payment includes both principal (the amount borrowed) and interest (the cost of borrowing). Only the interest portion is deductible. The principal is not. Your loan statement should show how much of each payment goes to interest and how much to principal.

What happens if I cannot prove my business mileage?

Without mileage records, the IRS will not allow your deduction. You cannot estimate or guess. If audited, you must show contemporaneous records — a log kept at or near the time you drove. Reconstructing records after the fact is not accepted.

Can I deduct interest on a business line of credit used to buy a car?

Yes, if the line of credit was used to purchase a business vehicle and you can document the business use. The type of loan does not matter; what matters is what the money was used for and how the vehicle is used.