Investment Interest Expense Calculator 2026 (and 2025): Form 4952, IRC §163(d), Schedule A

Investment Interest Expense Deduction — IRC §163(d) Parameters
Item	Tax Year 2026	Tax Year 2025
Current-year deduction limit	Net investment income	Net investment income
Carryforward of disallowed interest	Indefinite	Indefinite
Qualified dividends in investment income by default	Excluded	Excluded
Net capital gain in investment income by default	Excluded	Excluded
Election (line 4g) to include QDIV or LTCG	Allowed; elected amount taxed at ordinary rates	Allowed; elected amount taxed at ordinary rates
Interest on debt to buy tax-exempt securities	Not deductible	Not deductible
Qualified residence interest counted as investment interest	No (excluded by §163(d)(3)(B)(i))	No
Passive-activity interest counted as investment interest	No (excluded by §163(d)(3)(B)(ii))	No
Reporting location	Schedule A line 9 (Form 4952 line 8)	Schedule A line 9 (Form 4952 line 8)
Investment advisory fees on line 5	Not deductible (2% misc; OBBBA made permanent)	Not deductible

How much investment interest can I deduct?

Under IRC §163(d), an individual can deduct investment interest only up to net investment income for the year. Margin interest and other interest on debt allocable to investment property go on Form 4952. If your investment interest exceeds your net investment income, the excess is not lost: it carries forward indefinitely as investment interest paid in the next tax year. The allowed amount is reported on Schedule A line 9 and only helps if you itemize.

What counts as investment interest expense?

Investment interest is interest you pay on debt allocable to property held for investment, most commonly margin interest on a brokerage account used to buy stocks or taxable bonds. Personal interest, qualified residence interest, passive-activity interest, capitalized interest, interest on debt to buy tax-exempt securities, and interest on insurance or annuity contracts issued after June 8, 1997 are not investment interest and are not deductible on Form 4952.

What is net investment income for Form 4952?

Net investment income is investment income minus investment expenses. Investment income is portfolio income such as taxable interest, ordinary dividends, annuities, and royalties from property held for investment. Qualified dividends and net long-term capital gain are excluded unless you elect to include them. Investment expenses are deductible expenses other than interest that are directly connected with producing investment income, such as depreciation or depletion on investment property.

Should I elect to include qualified dividends or capital gains?

The election lets you treat qualified dividends and net capital gain as ordinary investment income on Form 4952 line 4g, which raises net investment income and frees up more interest to deduct in the current year. The trade-off is that the amount you elect loses the preferential capital-gain rate and is taxed as ordinary income on Schedule D or the qualified-dividends worksheet. The election usually only pays when you have a large interest carryforward and your ordinary rate is close to the capital-gain rate.

Where does the deduction go on my tax return?

The amount on Form 4952 line 8 is reported on Schedule A (Form 1040) line 9 as investment interest expense, separate from home mortgage interest on line 8a. Because it is an itemized deduction, it reduces your tax only if your total itemized deductions exceed your standard deduction. Estates and trusts report it on Form 1041 line 10 instead.

Does the carryforward expire?

No. Disallowed investment interest from Form 4952 line 7 carries forward indefinitely under IRC §163(d)(2) and is treated as investment interest paid or accrued in the following tax year. There is no time limit, no age limit, and the carryforward survives a change in your investment activity. It is recovered when you have enough net investment income to absorb it, including in years when you elect to include qualified dividends or capital gains.

Is margin interest the same as investment interest?

Margin interest charged by your broker on a loan used to buy stocks or taxable bonds is the most common kind of investment interest. It is deductible on Form 4952 subject to the net-investment-income limit. Margin interest used to carry tax-exempt securities, such as municipal bonds, is not deductible at all. If you used margin for several purposes, you must allocate the interest by the proportion of the loan tied to taxable investments.

Does the OBBBA change the investment interest deduction?

No. The One Big Beautiful Bill Act did not amend IRC §163(d). The rule that investment interest is deductible only up to net investment income, the qualified-dividend and capital-gain election, and the indefinite carryforward are unchanged for 2025 and 2026. The Act made permanent the suspension of miscellaneous itemized deductions that ended the deduction of investment advisory fees as Schedule A line 5 expenses, but those fees were already not investment expenses on Form 4952 line 5.

Investment Interest Expense Calculator

2026 and 2025 Form 4952 Parameters

How the Form 4952 Calculation Works

Step 1: Total Investment Interest (Lines 1-3) Confirmed

Step 2: Investment Income (Lines 4a-4f) Confirmed

Step 3: The Election on Line 4g Confirmed

Step 4: Net Investment Income (Line 6) Confirmed

Step 5: Deduction and Carryforward (Lines 7-8) Confirmed

Real-World Examples

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