Is the Interest You Pay Deductible? It Depends Where the Money Went

Borrow money and pay interest — is it deductible? The honest answer from my desk: it depends entirely on what the loan proceeds were used for. The tax code does not care what the loan is called or what collateral secures it nearly as much as it cares where the dollars went. Here is the map, current under post-OBBBA law.

Personal interest — no

Credit cards, personal car loans, appliance financing: not deductible. Full stop.

Investment interest — limited

Interest on debt used to buy investments (stocks, land, mutual funds) is deductible — but only up to your net investment income, and only if you itemize. Interest on debt used to carry tax-exempt investments is not deductible at all. Since miscellaneous itemized deductions were suspended in 2018 and that suspension was made permanent by the 2025 tax law, investment expenses rarely reduce the income figure anymore, so for most people the cap is simply their taxable investment income. Disallowed amounts carry forward.

Home mortgage interest — capped

Interest on your primary home plus one second home is deductible if you itemize, on up to $750,000 of acquisition debt ($1 million for debt incurred before December 16, 2017). The 2025 tax law made the $750,000 cap permanent. Acquisition debt means money used to buy, build, or substantially improve the home, secured by the home. Refinance and pull cash out for anything else, and the interest on the excess is generally not deductible as mortgage interest — though the tracing rules below may salvage it if the cash went to a business or investment use.

Passive activity interest — netted against passive income

Interest on debt for activities you do not materially participate in (most commonly rental real estate) generally only helps to the extent passive income covers passive expenses. Active rental owners get a special allowance of up to $25,000 of losses, phasing out between $100,000 and $150,000 of adjusted gross income.

Trade or business interest — generally fully deductible

Interest on debt for a business you materially participate in is generally deductible in full. Very large businesses — those over an inflation-adjusted gross-receipts threshold in the low tens of millions — face the section 163(j) limitation, but most owner-operated firms are exempt.

Student loan interest — above the line

Up to $2,500 per return, per year, no itemizing required. The deduction phases out at higher incomes (the ranges adjust for inflation), is unavailable to married-filing-separate filers and dependents, and mixed-use loans do not qualify.

The tracing rules: follow the money

Because each category carries different limits, the IRS allocates interest by tracing the loan proceeds to what they actually paid for. Borrow against your house to fund your business, and that interest may be business interest. Borrow from the business to pay off a personal card, and it becomes nondeductible personal interest. The paper trail decides — which is why how you move borrowed money between accounts matters as much as the borrowing itself.

Structuring debt so the interest lands in the right category is planning work, and it pays for itself. Attach your loan picture with the paperclip in the chat — we scope and quote the work in writing after intake — or start with the free Chapter 8 sample of the Guide.