What Is Personal Interest Under Federal Tax Law?

Under federal tax law, the personal interest you pay on everyday debts is not deductible. Credit card balances, most car loans, personal lines of credit, and interest the IRS charges on unpaid taxes all fall into this category, and none of it reduces your taxable income. The personal interest tax deduction that existed before 1987 was phased out by 1991, and today only a handful of borrowing purposes — home mortgages, student loans, investment borrowing, and (for 2025 through 2028) certain new car loans — sit outside the personal category and generate a tax benefit.¹

What Personal Interest Means

Internal Revenue Code Section 163(h) defines personal interest as a catch-all. It is any interest you pay that does not fit one of the named exclusions: trade or business interest, investment interest, passive activity interest, qualified home mortgage interest, certain estate tax interest, qualified education loan interest, and (starting in 2025) qualified passenger vehicle loan interest. If your borrowing doesn’t fit one of those buckets, the interest is personal, and you get no tax benefit from paying it.¹

The classification follows the use of the money, not the type of loan. A home equity line of credit used to renovate your kitchen may qualify as deductible mortgage interest. The same line of credit used to fund a vacation produces personal interest. This “follow the money” approach comes from the IRS interest-tracing regulations and means the name on the loan matters less than what you actually did with the proceeds.²

Debts That Generate Non-Deductible Personal Interest

Credit card debt is the largest source of personal interest for most households. As of early 2026, average credit card APRs sit around 24%, with offers ranging from roughly 20% for borrowers with strong credit to 27% or higher for weaker profiles. Because cards fund groceries, clothing, travel, and other consumption, nearly all interest charged on them is personal.³

Other typical sources:

Auto loans on personal vehicles. Interest on a car you drive for commuting and errands has historically been fully personal, though a temporary carve-out now applies to certain new vehicle loans.³
Personal lines of credit used for furniture, appliances, vacations, or emergency household expenses.
Interest the IRS charges on unpaid income taxes. Treasury regulations treat underpayment interest on individual income taxes as non-deductible personal interest, even when the underlying income came from your business.
Life insurance policy loans used for personal purposes. A separate provision of the tax code also restricts interest deductions on loans used to carry life insurance policies in many circumstances.⁴

Interest That Escapes the Personal Category

Several kinds of interest that individuals pay are specifically excluded from the personal classification, which is why they can reduce your tax bill.

Home Mortgage Interest

Mortgage interest on your primary home or a second home is treated as qualified residence interest rather than personal interest. You can deduct interest on up to $750,000 of mortgage debt taken out after December 15, 2017 ($375,000 if married filing separately). Mortgages originating before that date have a higher cap of $1 million.⁵ This is by far the largest interest-related tax benefit available to most individuals.

Student Loan Interest

Interest on qualified education loans is treated as an adjustment to income, so you can deduct up to $2,500 per year without itemizing.⁶ The deduction phases out between $85,000 and $100,000 of modified adjusted gross income for single filers, and between $170,000 and $200,000 for joint filers. Above those upper limits, no deduction is available.

Investment Interest

When you borrow to buy stocks, bonds, or other income-producing assets, the interest is investment interest, not personal interest. You report it on Form 4952, and the deduction is capped at your net investment income for the year, with any excess carrying forward.⁷ The borrowed money must actually go toward assets expected to produce taxable income. Borrow against a brokerage account to buy a boat, and the interest is personal.

The Temporary New Car Loan Deduction for 2025 Through 2028

For tax years 2025 through 2028, a new provision lets you deduct up to $10,000 per year in interest on a qualifying new vehicle loan. This is the first time since 1990 that car loan interest has been partially deductible for personal use.⁸

The requirements are specific. The vehicle must be new, meaning original use starts with you. It must be manufactured primarily for public road use, and its final assembly must take place in the United States. The loan must be secured by a first lien on the vehicle, and you must include the vehicle identification number on your return. Fleet purchases, commercial vehicles, lease financing, and vehicles with salvage titles do not qualify.⁸

Income limits also apply. The deduction begins phasing out once your modified adjusted gross income exceeds $100,000 for single filers or $200,000 for joint filers, dropping by $200 for every $1,000 of income above the threshold. It disappears entirely at $150,000 for single filers and $250,000 for joint filers.⁸ Unlike most interest deductions, this one is available whether or not you itemize.³

Mixed-Use Debt and the Tracing Rule

If you run business and personal charges through the same credit card or line of credit, the IRS applies interest-tracing rules from Treasury Regulation 1.163-8T. Interest is classified based on what the borrowed money actually paid for, not the type of account or what secures it.²

If 60% of a card’s charges in a billing cycle are legitimate business expenses and 40% are personal, then 60% of that month’s interest is potentially deductible as business interest and the other 40% is non-deductible personal interest. You need to run this allocation for every mixed-use billing period, which is why separate cards for business and personal spending save both money and paperwork.

One useful shortcut: if you deposit loan proceeds into an account and make an expenditure from that account within 15 days, you can treat the expenditure as paid from those proceeds.² Outside that window, a more complex ordering rule applies, and clean records become essential.

Penalties for Misclassifying Personal Interest

Passing personal interest off as a business deduction is a common audit trigger, and the penalties scale with intent. If the IRS finds you were careless or ignored the rules, the accuracy-related penalty is 20% of the resulting tax underpayment.⁹ The same 20% applies to a substantial understatement, defined as one exceeding the greater of 10% of the tax you should have reported or $5,000.

If the IRS shows the misclassification was intentional, the penalty rises to 75% of the underpayment attributable to fraud.¹⁰ Once any portion of the underpayment is shown to be fraudulent, the whole underpayment is presumed fraudulent unless you can prove otherwise. Add the back taxes and the accrued interest on top, and the total cost of getting caught can easily exceed the deduction you were trying to claim.

1
Office of the Law Revision Counsel. 26 USC 163 Interest – Section: Disallowance of Deduction for Personal Interest
2
eCFR. 26 CFR 1.163-8T Allocation of Interest Expense Among Expenditures
3
Internal Revenue Service. Topic No. 505 Interest Expense
4
Office of the Law Revision Counsel. 26 USC 264 Certain Amounts Paid in Connection With Insurance Contracts
5
Internal Revenue Service. Publication 936 (2025) Home Mortgage Interest Deduction
6
Internal Revenue Service. Topic No. 456 Student Loan Interest Deduction
7
Internal Revenue Service. Form 4952 Investment Interest Expense Deduction (2025)
8
Office of the Law Revision Counsel. 26 USC 163 Interest – Section: Special Rules for Taxable Years 2025 Through 2028 Relating to Qualified Passenger Vehicle Loan Interest
9
Internal Revenue Service. Accuracy-Related Penalty
10
Office of the Law Revision Counsel. 26 USC 6663 Imposition of Fraud Penalty