The Net Investment Income Tax (NIIT): History, Purpose, and How to Avoid It

By Bob Lobclaw · August 10, 2026

NIIT stands for the Net Investment Income Tax — a 3.8% surtax on interest, dividends, capital gains, and other investment income for people above certain income thresholds. It’s officially Internal Revenue Code Section 1411, but people encounter it informally, usually as an unpleasant surprise on a tax return, since nothing about a 1099 warns you it’s coming. It applies on top of whatever ordinary income tax or capital gains tax you already owe on that income — it doesn’t replace anything, it stacks.

Where it came from

The NIIT was created by the Health Care and Education Reconciliation Act of 2010, the reconciliation bill that accompanied the Affordable Care Act, and took effect on January 1, 2013. It’s often nicknamed the “Medicare surtax,” and the 3.8% rate wasn’t arbitrary: it was set to mirror the combined 2.9% employer-plus-employee Medicare payroll tax rate plus the 0.9% Additional Medicare Tax that the same law imposed on wages above similar thresholds. The idea was to close a long-standing gap — wages had always funded Medicare through payroll tax, while investment income never had, letting high earners with large portfolios contribute proportionally less to the program than a wage-earner at the same income. Despite the nickname, the two taxes aren’t administratively identical: the Additional Medicare Tax on wages is credited directly to the Medicare Hospital Insurance Trust Fund, while NIIT revenue instead flows into the federal government’s general fund, where it helped offset the broader cost of the ACA’s coverage expansion rather than Medicare specifically.

How the tax is actually calculated

NIIT applies to the lesser of two numbers: your net investment income for the year, or the amount by which your Modified Adjusted Gross Income exceeds your filing threshold. That “lesser of” structure matters — someone with $400,000 of MAGI and just $10,000 of investment income only owes 3.8% on the $10,000, not on the full amount over the threshold. Conversely, someone with $600,000 of MAGI who is $400,000 over the threshold, but only $50,000 of which is investment income, owes tax on the smaller $50,000 figure.

The individual thresholds are a fixed, unindexed part of the statute — unlike almost every other number in the tax code, they haven’t moved a dollar since 2013. Ordinary income tax brackets, the standard deduction, and IRMAA tiers have all crept upward with inflation over that span; these thresholds haven’t, which means more households cross into NIIT territory every year purely from wage growth and portfolio appreciation, without their real purchasing power having changed at all. Trusts and estates face a far lower threshold that does get a small annual inflation adjustment, which is why many trusts are structured to distribute income out to beneficiaries rather than retain it — shifting the income onto an individual return where the threshold is dramatically higher.

What counts as net investment income

The retirement-account exclusion trips people up because of how it interacts with the MAGI side of the calculation. A traditional IRA or 401(k) distribution is never itself net investment income — it’s excluded outright — but it still raises your MAGI dollar for dollar, which can push you over the threshold and expose other income, like dividends or capital gains sitting in a taxable brokerage account, to the tax. A large Required Minimum Distribution doesn’t get taxed under NIIT itself, but it can be the exact thing that makes your taxable-account dividends taxable under it. See the RMDs article for how those distributions are calculated in the first place.

How to reduce or avoid it

There’s no way to make investment income itself exempt from NIIT once you’re over the threshold, but there are several legitimate ways to manage the two inputs — MAGI and net investment income — that determine whether, and how much, you owe.

• Hold municipal bonds. Interest from most municipal bonds is excluded from both regular taxable income and NIIT, making them one of the few assets that avoid the tax on the income itself rather than just managing around it.
• Harvest capital losses. Realized losses net directly against realized gains before the NIIT calculation runs, so tax-loss harvesting reduces net investment income the same way it reduces your capital gains tax bill.
• Spread large gains across years. An installment sale, or simply timing when you realize a large capital gain, can keep MAGI under the threshold in any single year instead of concentrating the whole gain — and the NIIT exposure that comes with it — into one filing.
• Use Qualified Charitable Distributions. A QCD sends IRA money directly to charity and excludes it from MAGI entirely, rather than including it and then deducting it. Since it can also satisfy an RMD, a QCD keeps that income from ever counting toward the MAGI side of the NIIT test. The QCD article covers the mechanics and dollar limits.
• Time Roth conversions carefully. A Roth conversion itself adds to MAGI in the year you convert and can trigger or increase NIIT exposure that year, but it permanently shrinks the pre-tax balance that would otherwise generate RMDs (and the MAGI that comes with them) for the rest of your life. Converting during lower-income years — the same bracket-filling logic used for IRMAA planning — can reduce lifetime NIIT exposure even though it raises MAGI in the conversion year itself. The Roth conversion strategies article walks through that timing tradeoff in more depth.
• Qualify as a real estate professional. Rental income is passive, and therefore subject to NIIT, by default. Someone who meets the IRS’s real estate professional material-participation tests can convert that income into active trade/business income, which falls outside NIIT entirely — a high bar involving specific hour thresholds, not just owning rental property.
• Use a charitable remainder trust for concentrated gains. Donating a highly appreciated asset to a CRT before selling lets the trust sell without triggering an immediate capital gain to you, replacing a single large MAGI spike with a smaller income stream spread over years.

NIIT vs. IRMAA: two different MAGI tripwires

NIIT is easy to confuse with IRMAA, the Medicare premium surcharge, because both are triggered by crossing a MAGI threshold and both disproportionately affect people with large investment portfolios or big one-time income events like Roth conversions or asset sales. But they’re separate systems: NIIT uses a MAGI definition specific to Section 1411, applies starting the same year the income is earned, and taxes only the investment-income portion of what’s over the threshold. IRMAA uses a different (though similar) MAGI figure, looks back two tax years, and surcharges Medicare Part B and Part D premiums rather than taxing income directly. A single large capital gain or Roth conversion can trigger both in the same filing, which is why managing MAGI broadly — not just for one tax or the other — matters more the closer you are to either threshold.

The bottom line

NIIT is a 3.8% surtax on investment income for higher earners, created in 2010 to help fund the ACA and effective since 2013, with thresholds that have never moved since. It can’t be eliminated once you’re solidly above the threshold, but because it depends on two separate inputs — MAGI and net investment income — there’s real room to manage both: holding tax-exempt bonds, harvesting losses, spacing out large gains, routing charitable IRA giving through QCDs, and timing Roth conversions all shrink either the numerator or the trigger that determines what you owe. The Roth vs. 401(k) comparison tool and the Data & Logic page cover how MAGI-driven thresholds like this one factor into the broader tax modeling on this site.

Educational content, not personalized financial advice — see the disclaimer.