The Net Investment Income Tax is a 3.8% surtax on investment earnings for higher-income taxpayers, and it applies to the smaller of two numbers: your net investment income for the year, or the amount your modified adjusted gross income exceeds the threshold for your filing status.1Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax The thresholds are $200,000 for single filers and heads of household, $250,000 for married couples filing jointly, and $125,000 for married filing separately. If your MAGI sits below the threshold for your status, you owe nothing regardless of how much investment income you had.
The Formula in Practice
Work the calculation in three steps. First, total your net investment income. Second, subtract your filing-status threshold from your MAGI to find the excess (if any). Third, multiply the smaller of those two figures by 3.8%.2Internal Revenue Service. Net Investment Income Tax
The “lesser of” structure has a useful consequence. Someone earning well above the threshold on wages but holding little investment income pays only on the investment income. Someone barely over the threshold with a large investment gain pays only on the MAGI excess. The tax always hits the smaller target.
What Counts as Net Investment Income
The categories pulled into net investment income are the ones you’d generally expect: interest, dividends, capital gains, rental and royalty income, non-qualified annuities, and income from passive business activities.2Internal Revenue Service. Net Investment Income Tax Capital gains from selling stocks, bonds, mutual funds, and real estate all count to the extent they’re included in your taxable income.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax
Business income is where it gets more nuanced. If you own a stake in a partnership or S corporation but don’t materially participate in daily operations, the income counts. If you materially participate, it doesn’t. Gains from selling those passive ownership interests generally count too, subject to a special rule limiting the includible gain to the portion attributable to certain assets.1Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax Trading in financial instruments or commodities is pulled in by the statute regardless of whether you’d otherwise call it active.
What the Tax Doesn’t Touch
Several common income types stay entirely outside the calculation: wages, unemployment compensation, Social Security benefits, alimony, and most self-employment income.2Internal Revenue Service. Net Investment Income Tax Tax-exempt municipal bond interest, VA benefits, and income from a business where you materially participate are also excluded.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax
The Section 121 home-sale exclusion carries through. The first $250,000 of gain on a primary residence ($500,000 for joint filers) that’s excluded from regular income tax is also excluded from net investment income. Only gain above the exclusion amount enters the calculation.4Internal Revenue Service. Questions and Answers on the Net Investment Income Tax Nonresident aliens don’t owe the tax at all.
Filing Status Thresholds and MAGI
The threshold that triggers the tax depends entirely on filing status:
- Single or head of household: $200,000
- Married filing jointly or qualifying surviving spouse: $250,000
- Married filing separately: $125,000
These figures have never been indexed for inflation, and nothing in the statute provides for future adjustment.4Internal Revenue Service. Questions and Answers on the Net Investment Income Tax More households cross them every year as wages and returns rise.
For most taxpayers, MAGI for this purpose equals the adjusted gross income on your return. It only diverges if you claim the foreign earned income exclusion under Section 911, which gets added back, or if you have certain income from controlled foreign corporations or passive foreign investment companies.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax
Deductions That Reduce the Base
You don’t pay 3.8% on gross investment income. The statute lets you subtract deductions properly allocable to that income.1Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax The IRS lists several categories: investment interest expense, investment advisory and brokerage fees, expenses tied to rental and royalty income, tax preparation fees, fiduciary expenses for estates and trusts, and state and local income taxes.4Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
The word “allocable” does real work. State income taxes paid on a mix of wages and investment income only reduce net investment income to the extent they trace to the investment portion. Advisory or preparation fees covering both sides get split the same way. If you deduct foreign income taxes instead of taking the foreign tax credit, some or all of that deduction may also reduce your net investment income.
Two Worked Examples
A single filer has $240,000 in MAGI and $60,000 of net investment income. The MAGI excess is $40,000 ($240,000 minus $200,000). Since $40,000 is smaller than $60,000, the tax applies to $40,000. The bill is $40,000 × 3.8% = $1,520.
Flip the numbers. A single filer has $240,000 in MAGI but only $15,000 in NII. The MAGI excess is still $40,000, but the NII is only $15,000. The tax applies to the smaller: $15,000 × 3.8% = $570.2Internal Revenue Service. Net Investment Income Tax
Home sales trip people up. A single filer earns $210,000 in wages and sells a home she’s lived in for a decade, with $400,000 of gain. The Section 121 exclusion removes $250,000, leaving $150,000 of recognized gain that counts as NII. Her MAGI is $360,000, so the MAGI excess is $160,000. The tax applies to the smaller: $150,000 × 3.8% = $5,700. Had her MAGI landed at $195,000 after the exclusion, she’d owe nothing because she’d be under the $200,000 threshold.4Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
The Real Estate Professional Exception
Rental income is normally passive, and passive income counts. If you qualify as a real estate professional for the year, though, your rental activities aren’t passive, and that income leaves the NIIT base.
Two tests must be met. More than half the personal services you performed across all businesses during the year must have been in real property trades or businesses where you materially participated, and you must have logged more than 750 hours in those activities. Hours worked as an employee in real estate don’t count unless you owned more than 5% of the employer. On a joint return, only one spouse needs to independently satisfy the professional requirements, though both spouses’ hours count toward material participation in a specific activity.5Internal Revenue Service. Publication 925 (2025), Passive Activity and At-Risk Rules
The IRS scrutinizes these claims closely. Contemporaneous logs of hours are essentially required if the classification is ever questioned.
Trusts and Estates
Trusts and estates owe the same 3.8% but at a much lower entry point. The tax kicks in once adjusted gross income exceeds the dollar amount where the highest income tax bracket starts, which for 2026 is $16,000.6Internal Revenue Service. 2026 Form 1041-ES Estimated Income Tax for Estates and Trusts The tax applies to the lesser of undistributed net investment income or that AGI excess.1Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax Income distributed to beneficiaries leaves the trust’s calculation and enters theirs. Estates and trusts report on Form 1041.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax
Reporting and Paying
Individuals calculate the tax on Form 8960. Part I lists gross investment income, Part II lists allocable deductions, and Part III applies the 3.8% rate to the taxable amount.7Internal Revenue Service. Form 8960 Net Investment Income Tax – Individuals, Estates, and Trusts The resulting tax flows to Schedule 2, Line 12, and from there to Form 1040, Line 23.8Internal Revenue Service. 2025 Instructions for Form 8960 – Net Investment Income Tax
Investment income usually isn’t withheld against, so a taxpayer who first learns about the NIIT at filing time may face an underpayment penalty on top of the tax. Two ways to cover it in advance: raise wage withholding by adding an amount in Step 4(c) of a new Form W-4 (the W-4 instructions specifically name the NIIT as a reason to run the IRS withholding estimator),9Internal Revenue Service. Form W-4 – Employee’s Withholding Certificate (2026) or make quarterly estimated payments using Form 1040-ES, whose worksheet directs taxpayers to include the NIIT.10Internal Revenue Service. 2026 Form 1040-ES Estimated Tax for Individuals
You avoid an underpayment penalty if the total balance at filing is under $1,000, or if withholding and estimated payments together cover at least 90% of the current year’s tax or 100% of last year’s (110% if last year’s AGI topped $150,000, or $75,000 if married filing separately).11Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty Most people subject to the NIIT already sit above the $150,000 line, so the 110% safe harbor is the practical benchmark. Paying 110% of last year’s total tax through withholding or estimates keeps you penalty-free no matter how the current year’s investment income lands.