When Does Net Investment Income Tax Kick In?

The Net Investment Income Tax kicks in the year your modified adjusted gross income crosses $200,000 if you file single, $250,000 if you file jointly, or $125,000 if you file married separately, and you have some form of investment income. The 3.8% rate then applies to whichever number is smaller: your net investment income for the year, or the dollars by which your MAGI exceeds your threshold. So the tax turns on two things at once, and having just one of them (a big salary with no investments, or investment income with a modest MAGI) is not enough to owe anything.¹

The MAGI Thresholds by Filing Status

The tax comes from Internal Revenue Code Section 1411, enacted as part of the Health Care and Education Reconciliation Act of 2010 and effective starting in 2013. It uses modified adjusted gross income to decide whether you’re in range:²

Married filing jointly or qualifying surviving spouse: $250,000
Single or head of household: $200,000
Married filing separately: $125,000

MAGI for this tax is generally the adjusted gross income on your return, with foreign earned income you excluded under Section 911 added back. Holders of interests in controlled foreign corporations or passive foreign investment companies may have further adjustments.¹

These dollar figures are fixed. The IRS does not index them for inflation, and the One Big Beautiful Bill signed in 2025 left both the thresholds and the 3.8% rate alone. Wage growth and rising asset values push more filers past the lines each year, so a household that was clearly under the threshold a few years ago may be crossing it now without any change in real income.¹

What Counts as Investment Income (and What Doesn’t)

Crossing the MAGI line only matters if you actually have net investment income. The categories that count include:³

Interest and dividends from savings accounts, bonds, and stocks
Capital gains from selling stocks, bonds, mutual funds, or real estate, to the extent included in taxable income
Rental and royalty income, including from investment property and mineral or intellectual-property rights
Non-qualified annuity income
Passive business income from an activity you own but don’t materially participate in
Income from a business that trades financial instruments or commodities

Several familiar income streams sit outside the tax entirely. Wages, salaries, and tips are the biggest exclusion. Unemployment benefits, Social Security payments, and alimony are also out. Self-employment income is excluded because it already carries the separate 15.3% self-employment tax. Distributions from 401(k) plans, 403(b) plans, traditional IRAs, Roth IRAs, and 457(b) plans do not count as net investment income either, though a large retirement distribution can still push your MAGI over the threshold and cause your other investment income to be taxed. Tax-exempt municipal bond interest is excluded as well.¹

Rental income sits on a line worth watching. If you own a rental and a manager handles everything, that income is passive and falls under the NIIT. If you’re a real estate professional who materially participates in the activity, the income can be treated as active and excluded. Material participation is measured under a set of IRS tests, the most direct one requiring more than 500 hours in the activity during the year.⁴

You don’t pay 3.8% on gross investment income. You subtract deductions properly allocable to that income first, and the result is net investment income. Investment interest expense is the most common one. Rental expenses like depreciation, repairs, and management fees offset rental income in the calculation.⁵

How the 3.8% Is Actually Calculated

Once you know your MAGI and your net investment income, the tax applies to the smaller of two figures: your net investment income, or the amount your MAGI exceeds the threshold.²

A single filer with $210,000 MAGI and $5,000 in net investment income is $10,000 over the threshold. Investment income is smaller, so the tax is 3.8% of $5,000, or $190. Flip it: if the same filer had $205,000 MAGI and $15,000 in investment income, the excess over the threshold ($5,000) is smaller, and the tax is again 3.8% of $5,000, or $190. The tax always attaches to the narrower slice.

Now take a married couple filing jointly with $240,000 in wages and $30,000 in investment income. MAGI is $270,000, so the excess is $20,000. Net investment income is $30,000. The tax is 3.8% of the smaller number, $20,000, producing $760. They had $30,000 in investment income, but only the portion that corresponds to the MAGI above the threshold gets taxed.

A Home Sale Can Push You Over

Selling a primary residence is where the NIIT surprises people. The Section 121 exclusion protects the first $250,000 of gain, or $500,000 for a married couple filing jointly, and that excluded portion is not investment income for NIIT purposes. Any gain above the exclusion is investment income, and if it also drives your MAGI past the threshold, the 3.8% follows.¹

Say a married couple sells a longtime home for $1.3 million with a $700,000 basis. The $600,000 gain becomes $100,000 of recognized gain after the $500,000 exclusion. Combined with $125,000 of other investment income and a total MAGI of $300,000, their excess over $250,000 is $50,000 and their total net investment income is $225,000. The tax is 3.8% of the smaller figure, $50,000, or $1,900. Homeowners who have never dealt with the NIIT before often don’t see that bill coming.

Trusts and Estates Cross the Line Much Sooner

If you’re reading this for a trust or estate rather than for yourself, the threshold works very differently. A trust or estate hits the NIIT once its adjusted gross income passes the dollar figure where the top ordinary tax bracket begins. For 2026, that is $16,000. The compressed brackets that apply to trusts make the tax far easier to trigger than for an individual.²

The tax applies to undistributed net investment income: total net investment income minus whatever was carried out to beneficiaries in distributions during the year. Distributing income to beneficiaries before year-end shifts the exposure from the trust’s $16,000 threshold to the beneficiary’s much higher individual threshold.

Reporting and Paying During the Year

When your MAGI crosses the threshold, you file Form 8960 with your return. Gross investment income goes on the top half, allocable deductions in the middle, and the resulting tax flows to Schedule 2 of Form 1040, line 12.⁵

The NIIT is covered by the estimated tax rules, so it can’t wait until April. If you expect to owe, build it into quarterly estimates or adjust W-2 withholding. An underpayment produces a penalty calculated as interest on the shortfall, figured quarter by quarter at the federal short-term rate plus three percentage points.¹

The usual safe harbors apply. You’re generally protected if your total payments through withholding and estimates equal at least 90% of the current year’s tax or 100% of last year’s total tax, rising to 110% when your AGI is above $150,000. W-2 withholding counts as paid evenly across the year regardless of when it was actually taken, which gives employees a mid-year fix: if a stock sale or other investment event is going to push you across the threshold, dialing up withholding for the rest of the year can cover the NIIT without setting off quarterly penalty math.

1
Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
2
Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax
3
Internal Revenue Service. Topic No. 559, Net Investment Income Tax
4
Internal Revenue Service. Publication 925 (2025), Passive Activity and At-Risk Rules
5
Internal Revenue Service. Instructions for Form 8960