Two owners each pay $18,000 of interest in a year. One deducts all of it against business income and never thinks about it again. The other gets nothing, because the interest went on Schedule A, the standard deduction was bigger, and the loan that paid for the business was secured by the house. Same money, same use, opposite results, and the difference is not the loan. It is which return the interest lands on, which depends on what the borrowed money was used for, and whether anyone can prove it.
This guide is for owners with personal and business borrowing side by side: what makes interest deductible, where each kind of interest is deducted, the tracing rule that decides the answer when a personal loan funds a business, the home equity trap, and how to keep the records that make the deduction survive.
| Interest on | Deductible? | Where | Limit |
|---|---|---|---|
| Home mortgage (buy, build, improve your home) | Yes, if you itemize | Schedule A | Interest on up to $750,000 of acquisition debt ($375,000 married filing separately); the cap is now permanent |
| Business loan, line of credit, equipment financing | Yes | Schedule C, E, F, or the entity's return (1065, 1120-S) | Generally none for businesses under about $32 million of gross receipts |
| Rental property mortgage | Yes | Schedule E, against rental income | Passive loss rules can defer the benefit |
| Loan to buy taxable investments | Yes, limited | Schedule A via Form 4952 | Up to net investment income; excess carries forward |
| Personal: credit cards, personal loans, most car loans | No | Nowhere | Exception: interest on a qualifying new-vehicle loan, up to $10,000 a year, 2025 through 2028 |
Interest on a loan used to buy, build or substantially improve your main or second home is deductible on Schedule A, on up to $750,000 of that acquisition debt. The catch is that Schedule A only helps when your itemized deductions exceed the standard deduction ($32,200 for a married couple filing jointly in 2026; $16,100 single). With state and local taxes now deductible up to $40,400 for 2026 (phasing down above roughly $505,000 of income), more owners in high-tax states itemize than did a few years ago, but a couple with $14,000 of mortgage interest, $12,000 of state taxes and a few thousand of charity may still be below the line, in which case the mortgage interest is worth nothing on the return. The deduction also does not reduce self-employment tax or the income that the qualified business income deduction is computed on; it is the least valuable dollar of interest an owner pays.
Interest on money borrowed for the business is an ordinary expense of the business. For a sole proprietor it reduces Schedule C profit, which reduces income tax and self-employment tax together. For an LLC or S-Corp it is deducted on the entity's return and flows through as lower K-1 income. There is no itemizing threshold, no standard deduction to clear, and for businesses under the gross receipts threshold (about $32 million) no limit on the amount. An owner in the 32% bracket who also pays self-employment tax saves roughly 40 cents on every dollar of Schedule C interest and, depending on state, zero to 32 cents on every dollar of Schedule A interest.
The rule that surprises owners is that the tax character of interest follows what the borrowed money was spent on, not what secures the loan and not whose name is on it. The interest tracing rules allocate each dollar of debt to the expenditure it funded. A personal loan whose proceeds bought equipment for the LLC produces business interest. A business line of credit whose proceeds paid for a family vacation produces personal interest, non-deductible, even though the bank statement says "business". Proceeds deposited into an account are treated as spent on the first expenditures out of that account, with a 30-day window in which you can choose which expenditure to allocate them to, which is why proceeds mixed into a personal checking account are so hard to trace after the fact.
For an owner who borrows personally and puts the money into a pass-through entity, the interest can be allocated according to how the entity used the money, and deducted in the same place as the entity's income. It is not automatic: the allocation has to be documented, the entity's use of the funds has to be identifiable, and the return has to report it in the right place, which for an S-Corp shareholder who borrowed to fund the company is typically Schedule E, with a note that the interest is on debt traced to the entity.
Home equity interest is deductible on Schedule A only when the borrowed money was used to buy, build or improve the home that secures it, and that rule is now permanent. A HELOC used to fund the business is not home mortgage interest at all for tax purposes. That sounds like bad news and is in fact the opposite: under tracing, the interest on the portion of the HELOC that went into the business is business interest, deductible on the business return with no itemizing required. The trap is the owner who does neither, listing the HELOC interest on Schedule A because the lender sent a Form 1098, losing it to the standard deduction, and never claiming it as business interest because nobody traced the draws. Where the same HELOC funded a kitchen and the LLC, the interest splits in proportion to the draws, and the split has to be on paper.
Interest on a mortgage on a rental property is deducted on Schedule E against the rental's income regardless of whether you itemize, and it is not subject to the $750,000 cap. If the rental runs a loss, the passive activity rules can defer the benefit until there is passive income or the property is sold, with an allowance of up to $25,000 of loss for owners who actively participate and have income under $100,000 (phasing out by $150,000). Interest on money borrowed to buy taxable investments (a margin loan, a loan to buy a stake in a business you do not materially participate in) is investment interest, deductible only up to net investment income for the year, with the excess carried forward. Owners with several entities regularly have all five kinds of interest in the same year, and the return is only right if each loan was traced when it was taken.
For each loan, keep the note or agreement, the account the proceeds landed in, the expenditures the proceeds funded with dates, and, where a loan funded more than one use, the allocation. For a loan whose proceeds went into an entity, keep the transfer record and the entity's entry (contribution or loan from member). For a HELOC, keep every draw and what it paid for. The interest each year then allocates itself, and the return can show business interest on the business schedule and home interest on Schedule A without argument. HaraPro records each loan as an instrument with the payments linked to it and the entity it belongs to, so the interest on the LLC's equipment loan, the mortgage on the rental and the HELOC draw that funded the company are already separated by use when the year closes; the personal finance page shows the owner's view, and our guide on quarterly estimated tax across multiple LLCs covers where the interest lands in the forecast.
Yes. Interest on money borrowed for the business is an ordinary business expense, deducted on Schedule C, E or the entity's return, with no itemizing required and no limit for businesses under about $32 million of gross receipts.
Yes, on up to $750,000 of debt used to buy, build or improve your main or second home, but only as an itemized deduction on Schedule A, so it helps only when your itemized deductions exceed the standard deduction ($32,200 joint, $16,100 single for 2026).
Not as home mortgage interest, since the money did not improve the home. Under the interest tracing rules the interest on the portion used for the business is business interest, deductible on the business return, provided you can document which draws went to the business.
For the character of the interest, no; tracing follows the use of the proceeds. It matters for who deducts it and where, and for the records: a personal loan whose proceeds funded an entity needs a documented contribution or member loan to the entity.
For a personal vehicle, no, except that interest on a qualifying loan for a new vehicle assembled in the United States is deductible up to $10,000 a year for 2025 through 2028, with income phase-outs. For a vehicle used in the business, the business-use share of the interest is a business expense.