Picture a customer who heard about "no tax on car loan interest" and walked in ready to buy. Their trade-in is underwater, so the balance gets rolled into the new loan. Under the final federal rules, the interest on that rolled-over balance won't count toward the deduction.
A tax break meant to help affordability skips one of the most common ways people finance a new car.
Final IRS Rule on Car-Loan Interest Deduction: Who Qualifies
The IRS and Treasury published the final rule on Sept. 8, setting out how buyers can deduct interest on qualifying new-vehicle loans:
✅ New vehicles with final assembly in the US
✅ Up to $10,000 in interest a year
⚠️ Reduced benefits above $100,000 in income for single filers and $200,000 for joint filers
❌ Interest on rolled-in negative equity
NADA and the American Financial Services Association asked regulators to include negative equity. The IRS and Treasury declined. That matters: nearly 30% of new-vehicle purchases with a trade-in included negative equity in Q2, with an average of $6,884 owed, according to Edmunds.
"For many consumers, there would be no purchase without this arrangement." Greg Evans, NADA vice president for regulatory affairs
The rule also creates new work for lenders, who now have to track how much interest is tied to negative equity. "There's never been a reason to break any of this stuff out," said AFSA General Counsel Philip Bohi. So far, use has been limited: about 1.4 million filers claimed the deduction for 2025, with an average deduction of more than $1,800.
What the Auto-Loan Tax Deduction Means for Dealers and F&I
Remember that a deduction lowers taxable income. It isn't a dollar-for-dollar credit. So an $1,800 deduction is worth only a fraction of that in actual tax savings for most buyers, which makes it hard to build a sales pitch around.
The bigger issue is complexity. Lenders now have to split interest between the vehicle and the negative equity, and customers may be surprised when their year-end statement shows less deductible interest than they expected.
Set honest expectations at the desk. If a customer is rolling in negative equity, tell them up front that part of their interest won't qualify.
The best way to protect a customer's trust is to make sure the tax break they expect is the one they actually get.
