Net Investment Income Tax (NIIT): The 3.8% Surtax Explained

What is the Net Investment Income Tax?

The Net Investment Income Tax (NIIT) is a 3.8% federal surtax imposed on the net investment income (NII) of individuals, estates, and trusts whose income exceeds specific modified adjusted gross income (MAGI) thresholds. It is codified in Internal Revenue Code Section 1411.

The NIIT is not a replacement for the regular capital gains tax — it is an additional tax layered on top of existing income taxes. For a high-income investor realizing long-term capital gains, the federal rate structure works as follows:

• Regular long-term capital gains rate: 0%, 15%, or 20% depending on taxable income
• NIIT surtax (if MAGI exceeds threshold): +3.8%
• Maximum combined federal rate on long-term capital gains: 23.8% (20% + 3.8%)

For short-term capital gains, the NIIT can similarly stack on top of ordinary income rates, though in practice the interaction depends on the specific calculation mechanics described in the How NIIT is Calculated section below.

For full coverage of the regular capital gains rate structure, see our companion article on Capital Gains Tax on Stocks.

Historical Context: The ACA and NIIT

The NIIT was enacted as part of the Health Care and Education Reconciliation Act of 2010, one of the legislative packages comprising the Affordable Care Act (ACA). The tax went into effect on January 1, 2013.

The NIIT was designed to apply an additional Medicare-related tax burden on investment income of higher-income taxpayers, roughly paralleling the additional 0.9% Medicare surtax on wages above the same income thresholds (though the wage-side surtax and the NIIT are separate taxes with separate calculations). Both surtaxes help fund the Medicare Hospital Insurance Trust Fund.

One notable feature of the NIIT thresholds: unlike most other tax provisions, they are not adjusted for inflation. The $200,000 single / $250,000 married filing jointly thresholds enacted in 2010 remain unchanged as of the 2025 tax year. Because wages, investment income, and asset values have generally grown since 2010, a larger portion of the taxpayer population has been drawn into NIIT exposure over time simply through income growth — a phenomenon sometimes called bracket creep.

There have been periodic proposals in Congress to expand, modify, or repeal the NIIT, but as of the 2025 tax year the tax remains in its original form. Because tax law can change, investors benefit from monitoring legislative developments relevant to the NIIT.

Who Pays NIIT: MAGI Thresholds

The NIIT applies when your modified adjusted gross income (MAGI) exceeds a threshold that depends on your filing status. For most taxpayers, MAGI for NIIT purposes is the same as regular adjusted gross income (AGI) with certain additions for foreign income exclusions and other items that are uncommon for most US-based investors.

These thresholds are not indexed for inflation. If your MAGI is below the applicable threshold, you owe no NIIT regardless of how much investment income you have. Once your MAGI exceeds the threshold, the NIIT applies only to the lesser of your net investment income or the amount by which your MAGI exceeds the threshold — not to all of your investment income. This mechanics is explained in detail in the How NIIT is Calculated section.

For estates and trusts, the NIIT threshold is much lower — it applies to the undistributed net investment income of a trust or estate once its income reaches the highest estate/trust tax bracket threshold (approximately $15,200 for the 2025 tax year). This considerably lower threshold makes the NIIT broadly applicable to trusts that accumulate investment income.

What Counts as Net Investment Income

The IRS defines net investment income as gross investment income minus certain deductions allocable to that income. The main categories of income that are included in NII are:

1. Capital Gains

Realized capital gains from the sale of stocks, bonds, mutual funds, ETFs, and other investment property are included in NII. This includes both short-term and long-term gains. Capital gains distributions from mutual funds are also included. Capital losses can offset capital gains in computing NII, similar to how they work for regular income tax purposes.

2. Dividends

Both ordinary dividends and qualified dividends are included in NII. Unlike the regular income tax, which taxes qualified dividends at preferential rates, the NIIT applies to all dividends equally at 3.8%. There is no lower rate for qualified dividends for NIIT purposes — the surtax applies to the full amount if the MAGI threshold is exceeded.

3. Interest Income

Taxable interest income — from bank savings accounts, certificates of deposit, corporate bonds, Treasury notes, and similar instruments — is included in NII. Tax-exempt municipal bond interest is excluded from NII itself (though it can affect MAGI, as discussed in the FAQ section below).

4. Rental Income from Passive Activities

Net rental income from passive rental activities is included in NII. A rental activity is generally considered passive unless the taxpayer qualifies as a real estate professional under IRS rules (discussed in the Real Estate Professionals section). Allowable deductions — such as depreciation, mortgage interest, property taxes, and maintenance — reduce net rental income before the NIIT calculation.

5. Royalties

Royalty income from passive activities — such as licensing intellectual property, mineral rights, or oil and gas royalties where the taxpayer is not actively participating — is generally included in NII.

6. Passive Business Income

Net income from a trade or business that is a passive activity for the taxpayer — meaning the taxpayer does not materially participate in the business — is included in NII. This can include income flowing from passive interests in partnerships, S corporations, and LLCs. Material participation rules under IRC Section 469 determine whether an activity is passive or active for a given taxpayer.

7. Gains from Passive Business Dispositions

Gains from the sale or disposition of property used in a passive trade or business, and gains from the sale of partnership interests or S corporation stock to the extent attributable to passive activities, are generally included in NII.

What Does Not Count as Net Investment Income

Several significant categories of income are specifically excluded from NII and are therefore not subject to the 3.8% surtax:

Wages and Self-Employment Income

Wages, salaries, tips, and other compensation for services rendered are not investment income and are not subject to NIIT. Self-employment income from a business in which the taxpayer materially participates is also excluded from NII. (These income types may, however, be subject to the separate 0.9% additional Medicare tax on wages and self-employment income above the same thresholds.)

Social Security Benefits

Social Security retirement and disability benefits are not included in NII and are not subject to NIIT. A portion of Social Security benefits can be included in regular taxable income for higher earners, but that taxable portion is still excluded from the NIIT calculation.

Active Business Income

Income from a trade or business in which the taxpayer materially participates is excluded from NII. For a business owner who actively works in their business and meets the material participation standards under IRC Section 469, the income flowing from that business is not investment income and is not subject to NIIT.

Distributions from Retirement Accounts

Distributions from traditional IRAs, 401(k) plans, 403(b) plans, 457 plans, SEP-IRAs, SIMPLE IRAs, and other qualified retirement plans are excluded from NII. Similarly, qualified distributions from Roth IRAs and Roth 401(k)s are not included in NII. While these distributions affect MAGI (for traditional accounts) and therefore can influence the NIIT threshold calculation, the distributions themselves are not NII.

Tax-Exempt Interest

Interest from qualifying municipal bonds that is excluded from federal gross income is also excluded from NII. The NIIT does not reach tax-exempt interest.

Gain from the Sale of a Primary Residence (Within the Exclusion)

Gain excluded from income under the Section 121 home sale exclusion ($250,000 for single filers, $500,000 for married filing jointly) is also excluded from NII. However, any gain on a home sale that exceeds the exclusion and is therefore included in gross income is subject to NIIT if the MAGI threshold is also exceeded.

How NIIT is Calculated

The NIIT is calculated as 3.8% multiplied by the lesser of:

1. Your net investment income, or
2. The amount by which your MAGI exceeds the applicable threshold for your filing status

This “lesser of” rule means the NIIT is applied to only the portion of investment income that falls above the threshold, capped at total NII. Three worked examples illustrate how this works:

The NIIT is calculated and reported separately from the regular income tax. It is not reduced by deductions such as the standard deduction, but it is reduced by deductions directly allocable to the production of investment income — such as investment interest expense, state and local taxes allocable to NII, and expenses related to rental income that is included in NII.

Use our Capital Gains Tax Calculator to model NIIT alongside regular capital gains tax for a more complete picture of your potential federal tax liability on investment transactions.

Reporting NIIT: IRS Form 8960

The NIIT is reported on IRS Form 8960 (Net Investment Income Tax — Individuals, Estates, and Trusts). Taxpayers who owe NIIT attach Form 8960 to their federal income tax return (Form 1040) and report the tax on Schedule 2, Line 12.

Form 8960 walks through the calculation in several parts:

• Part I — Net Investment Income: Lists the components of gross NII (interest, ordinary dividends, annuity income, royalties, rents, capital gains, and passive income) and subtracts allowable deductions to arrive at total NII.
• Part II — MAGI: Calculates MAGI and determines how much it exceeds the applicable threshold.
• Part III — Tax Computation: Applies 3.8% to the lesser of NII or the MAGI excess.

If you use tax preparation software, Form 8960 is generally completed automatically based on data entered elsewhere in your return. If your investment income and MAGI are close to the NIIT threshold, reviewing the completed Form 8960 can help you verify the calculation. Tax preparers and CPAs will include Form 8960 as part of a complete federal return for affected taxpayers.

For estimated tax purposes, the NIIT is included in your total estimated federal tax liability. If you regularly have significant investment income and MAGI above the threshold, you may need to include NIIT in quarterly estimated tax payments to avoid underpayment penalties.

NIIT and Roth Conversions

A Roth IRA conversion — moving funds from a traditional IRA to a Roth IRA — is a taxable event. The converted amount is included in gross income (and MAGI) in the year of the conversion. However, the conversion itself is not classified as net investment income and is not directly subject to NIIT.

The indirect effect, however, is significant. When a Roth conversion increases MAGI, it can:

• Push MAGI above the NIIT threshold for the first time, causing investment income that would otherwise have been NIIT-free to become subject to the 3.8% surtax.
• Increase the amount by which MAGI exceeds the threshold, potentially subjecting more NII to the NIIT (up to the total NII amount).

This interaction illustrates why multi-year tax modeling — including the impact on NIIT — is commonly considered when evaluating the timing and sizing of Roth conversions, particularly for individuals near the MAGI threshold.

NIIT and Real Estate Professionals

Under the general NIIT rules, net rental income from passive real estate activities is included in net investment income and is subject to the 3.8% surtax for above-threshold taxpayers. However, there is an important exception: real estate professionals who materially participate in their rental activities may be able to exclude that rental income from NII.

Qualifying as a Real Estate Professional

To qualify as a real estate professional for tax purposes under IRC Section 469(c)(7), a taxpayer must meet two tests:

1. More than half of the personal services the taxpayer performs in all trades or businesses during the tax year are performed in real property trades or businesses in which the taxpayer materially participates.
2. The taxpayer performs more than 750 hours of services during the tax year in real property trades or businesses in which the taxpayer materially participates.

For a married couple filing jointly, only one spouse needs to qualify as a real estate professional — but the qualifying spouse must satisfy both tests independently.

Material Participation in Each Rental Activity

Qualifying as a real estate professional alone is not sufficient. The taxpayer must also materially participate in each specific rental property (or elect to group all rental properties into a single activity). Material participation requires meeting one of several tests, most commonly spending more than 500 hours in the activity during the year, or performing substantially all of the participation in the activity.

Real estate professional status and its application to NIIT is a complex area with significant documentation requirements (time logs are important). Investors with substantial rental income should work with a qualified tax professional experienced in real estate taxation to evaluate whether and how these rules apply to their specific situation.

NIIT Planning Considerations

The following are general educational concepts that illustrate how the structure of the NIIT interacts with common investment and tax decisions. None of the following constitutes personalized tax guidance. Always consult a qualified tax professional for advice specific to your situation.

Tax-Advantaged Accounts Reduce NII

Investment income earned inside a traditional 401(k), traditional IRA, or Roth account is not subject to NIIT in the year it is earned. Dividends, interest, and capital gains within these accounts grow without triggering NIIT. Traditional account distributions, when taken, increase MAGI and affect the NIIT threshold calculation for that year — but the distributions themselves are not NII. Roth account qualified distributions do not increase MAGI and do not affect the NIIT threshold at all.

Offsetting NII With Losses and Deductions

Capital losses realized in a taxable account reduce NII in the same way they reduce regular capital gains. Harvesting capital losses — selling securities with embedded losses — can reduce NII and therefore NIIT exposure, in addition to offsetting regular capital gains tax. Deductions directly allocable to investment income categories (such as investment interest expense under IRC Section 163(d)) also reduce NII directly.

Material Participation in Business Activities

Income from businesses in which the taxpayer materially participates is excluded from NII. For investors who have ownership interests in operating businesses, increasing material participation — to the extent it reflects genuine business involvement — can shift income from the passive (NII-included) category to the active (NII-excluded) category.

MAGI Management

Because NIIT is triggered by MAGI exceeding the threshold, managing MAGI is relevant to NIIT exposure. Contributions to traditional 401(k) and IRA accounts reduce MAGI (unlike Roth contributions, which do not). Health Savings Account (HSA) contributions also reduce MAGI. For individuals near the NIIT threshold, the above-the-line deductions that reduce MAGI may be relevant to whether and how much NIIT applies.

Municipal Bonds in High-MAGI Portfolios

Tax-exempt interest from municipal bonds is excluded from NII and not subject to NIIT. For taxable accounts of investors well above the MAGI threshold, municipal bonds can offer interest income free of both regular income tax and NIIT — though this benefit must be weighed against the typically lower pre-tax yield of municipal bonds compared to taxable bonds of similar quality. Use our Capital Gains Tax Calculator alongside a tax-equivalent yield calculation to assess relative after-tax value. For more on investment income terminology, see our Investment and Tax Glossary.

Frequently Asked Questions