Form 4952, Investment Interest Expense Deduction, works out how much interest on loans taken out to buy investments you can deduct, and how much carries forward. Your deduction is limited to your net investment income, and anything disallowed carries forward to future years. Individuals usually enter the deductible amount on Schedule A (Form 1040), line 9, so you only benefit if you itemize.
The classic case is a margin loan used to buy shares, but it covers any loan, or part of a loan, allocable to property held for investment. Everything below comes from Form 4952 for 2026 and its instructions, and the figures are as of October 2026.
Do you need to file Form 4952?
Individuals, estates and trusts must file it to claim a deduction for investment interest expense. But you don't have to file if all three of these apply:
- Your investment income from interest and ordinary dividends, minus any qualified dividends, is more than your investment interest expense.
- You don't have any other deductible investment expenses.
- You don't have any carryover of disallowed investment interest expense from 2025.
What counts as investment interest, and what doesn't
Investment interest expense is interest paid or accrued on a loan, or part of a loan, allocable to property held for investment, regardless of when you took the loan out. It includes investment interest reported to you on a Schedule K-1 from a partnership or S corporation.
| Counts | Doesn't count |
|---|---|
| Interest on a margin loan used to buy shares | Personal interest, including qualified residence interest |
| Your share of investment interest on a Schedule K-1 | Interest allocable to a passive activity, including rentals |
| Interest on a working interest in oil or gas you held without limited liability and didn't materially participate in | Interest that's capitalized, such as construction interest |
| Interest related to tax-exempt interest income |
If one loan paid for several things, you may have to split the interest between investment, personal, business, mortgage and passive uses, because each follows different rules.
Net investment income, the ceiling on your deduction
Part II works out the limit. Gross income from property held for investment includes interest, ordinary dividends, annuities and royalties not earned in the ordinary course of a trade or business. You enter qualified dividends separately on line 4b, and net gain from selling investment property on line 4d, with the net capital gain part on line 4e.
Here's the trade-off most people don't see coming. Qualified dividends and net capital gain are generally left out of investment income. You can elect on line 4g to include some or all of them, which raises your ceiling and lets you deduct more interest now. But whatever you elect to include loses the lower qualified dividends and capital gains rates and is taxed as ordinary income. Once made, the net capital gain election can be revoked only with IRS consent.
How to fill in Form 4952
- Line 1: investment interest expense paid or accrued in the year, including amounts from a Schedule K-1.
- Line 2: any disallowed investment interest carried over from last year.
- Lines 4a to 4g: gross investment income, qualified dividends, net gains, and any election to include qualified dividends or capital gain.
- Lines 4h to 6: add up investment income on line 4h, subtract investment expenses on line 5, and land on net investment income on line 6.
- Line 7: the amount you carry forward to next year.
- Line 8: your deduction, which individuals generally enter on Schedule A (Form 1040), line 9.
There are two routing exceptions. Interest attributable to royalties goes on Schedule E, and interest for a trade or business that isn't passive goes on the schedule where you report that business's expenses. If you make the line 4g election, use the Schedule D Tax Worksheet in the Schedule D instructions to work out your tax.
Estates, trusts and foreign tax credit filers
Estates and trusts use the same form. They generally enter the line 8 deduction on Form 1041, line 10, again with business interest that isn't passive going on the schedule for that business. Where they make a line 4g election with amounts on line 4e, they use the Schedule D Tax Worksheet in the Schedule D (Form 1041) instructions.
If you file Form 1116 for the foreign tax credit, the instructions flag one more choice. The line 4g amount is normally treated as coming first from net capital gain and then from qualified dividends, because that gives the least tax. You can choose to treat more of it as qualified dividends instead, which can matter for the credit calculation.
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A few traps
- Deducting mortgage interest here. Qualified residence interest is personal interest for this form, and it isn't investment interest.
- Forgetting the carryforward. Disallowed interest doesn't vanish; it waits for a year with enough net investment income.
- Electing on line 4g without checking the tax. The election swaps a deduction now for ordinary rates on gains and dividends that would otherwise be taxed more lightly.
- Ignoring the alternative minimum tax. Deductible interest expense may be an adjustment for AMT, so check Form 6251 too.
- Missing the at-risk rules. If any of the interest relates to an activity where you aren't at risk, Form 6198 comes into play.
The verdict
If you borrow to invest and you itemize, Form 4952 is how that interest becomes a deduction, and the carryforward means none of it's wasted. If you don't itemize, the form won't help this year, but filing to track the carryover can still pay off later. Be slow and deliberate with the line 4g election: run the numbers both ways before you give up the lower rates.
Frequently asked questions
What is Form 4952 used for?
It figures how much investment interest expense you can deduct for the year and how much you carry forward.
What limits the investment interest deduction?
Your deduction is limited to your net investment income. Any disallowed amount carries forward to future years.
Is Form 4952 always required?
Not if your interest and ordinary dividend income minus qualified dividends exceeds your investment interest, you have no other deductible investment expenses, and you have no carryover from 2025.
Where does the Form 4952 deduction go?
Individuals generally enter it on Schedule A (Form 1040), line 9, with exceptions for royalty and non-passive business interest.
Is mortgage interest investment interest?
No. Qualified residence interest is personal interest and isn't included.
What is the line 4g election?
An election to treat qualified dividends or net capital gain as investment income. It raises your limit but those amounts lose the lower tax rates.
