Net Investment Income Tax (NIIT): The 3.8% Surtax on Your Stock Gains and Dividends

NIIT at a Glance

What Is the Net Investment Income Tax?

The Net Investment Income Tax (NIIT) is a 3.8% surtax on investment income, created by the Affordable Care Act in 2013 (IRC §1411) to help fund Medicare. It applies on top of — not instead of — whatever ordinary income tax or capital gains tax you already owe on that income.

The tax applies to the lesser of two numbers: your net investment income for the year, or the amount by which your modified adjusted gross income (MAGI) exceeds the threshold for your filing status. Whichever number is smaller is what gets taxed at 3.8%.

The "lesser of" mechanic means the tax behaves in two distinct phases as your income rises. Just above the threshold, NIIT climbs quickly because your excess MAGI is the smaller number and grows dollar-for-dollar. Once your excess MAGI grows past your total NII, the tax flattens out — from that point forward, the full NII amount is taxed no matter how much higher your income climbs. The chart below shows this kink clearly for a filer with a fixed $50,000 of net investment income.

Below $200,000 MAGI, the line sits flat at zero — no NIIT applies at all. Between $200,000 and $250,000, it climbs steeply as excess MAGI grows. Past $250,000, it flattens permanently at $1,900 (3.8% of the full $50,000 NII) — the tax bill stops growing even as MAGI keeps climbing, because NII is now the smaller of the two numbers in the formula.

Why NIIT Exists — and Who It Was Designed to Hit

Before 2013, investment income (dividends, interest, capital gains) was subject to income tax but never to a Medicare-style payroll tax the way wages are — employees and employers each pay 1.45% Medicare tax on wages, but a retiree living entirely off dividends and bond interest paid nothing toward Medicare on that income. The Affordable Care Act's drafters closed this gap for higher earners by layering the 3.8% NIIT on top of investment income once MAGI crosses the threshold, explicitly modeled to parallel (though not identical to) the 2.9% combined Medicare payroll tax rate on wages.

Because the $200K/$250K thresholds were fixed in 2013 dollars and have never been indexed for inflation, the tax has quietly expanded its reach every year since — a household earning $200,000 in 2013 was solidly upper-middle-class; a household earning the same nominal $200,000 today has meaningfully less real purchasing power, yet faces the identical NIIT exposure. This is sometimes called "bracket creep by omission," and it means more taxpayers cross the threshold each year purely from wage growth and portfolio appreciation, without any change in the law itself.

How Much NIIT Really Adds to Your Top Rate

The 3.8% surtax sounds small in isolation, but it meaningfully raises the effective top marginal rate on every category of investment income once you're exposed to it. Municipal bond interest is entirely unaffected (it's excluded from NII), while ordinary-taxed income — non-qualified dividends and taxable interest — sees the largest absolute jump.

Real-World Scenarios: Who Actually Gets Hit

• The high-earning W-2 employee with a taxable brokerage account: a couple earning $300,000 in combined salary who also hold a $500,000 taxable investment account generating $20,000/year in dividends and gains will owe the full 3.8% on that $20,000 every year, since their wage income alone already exceeds the $250,000 MFJ threshold — this is the most common and least avoidable NIIT scenario.
• The retiree with a pension and dividend portfolio: a retired couple with $180,000 in pension and Social Security plus $90,000 in dividends and capital gains has $270,000 total MAGI — $20,000 over the threshold — so NIIT applies to the lesser of their $90,000 NII or $20,000 excess, meaning only $20,000 is taxed at 3.8% ($760), not the full $90,000.
• The founder or employee selling company stock: an employee who exercises options or sells RSU shares in a liquidity event can see MAGI spike into the millions in a single year purely from the stock sale (a capital gain, which is NII) — in this scenario, NIIT typically applies to the entire gain since excess MAGI will far exceed even a very large NII figure.
• The landlord with several rental properties: rental income and gain on sale of investment property are both NII by default, but a landlord who qualifies as a real estate professional (750+ hours/year materially participating) can reclassify that income as active, removing it from NII entirely — a meaningful planning opportunity for full-time real estate investors.

What Counts as Net Investment Income

Worked Example: NIIT Bill at Different Income Levels

Single filer with $50,000 in net investment income (dividends + capital gains combined) at various total MAGI levels:

Notice the bill caps out once excess MAGI exceeds your NII — beyond that point, the full $50,000 of investment income is taxed at 3.8% regardless of how much higher your total income climbs. The 3.8% is applied on top of whatever ordinary or capital-gains rate already applies, so a high earner's effective top rate on long-term gains becomes 20% + 3.8% = 23.8%, and on non-qualified dividends or interest, 37% + 3.8% = 40.8%.

NIIT and Your Stock Portfolio: What It Means for Asset Location

For most BriMindInvest readers, NII isn't rental income or a business sale — it's the dividends, interest, and capital gains generated by a stock and ETF portfolio. Once you're near or above the threshold, how you structure that portfolio starts to matter as much as what's in it, because different types of stock-market income carry very different combined tax rates once NIIT is added on top.

A few practical takeaways for a taxable brokerage account once you're exposed to NIIT:

• Qualified-dividend blue-chip stocks and Dividend Aristocrats carry the same 23.8% top combined rate as long-term capital gains — the most tax-efficient category of stock-market income for a taxable account.
• REITs and BDCs (see our guides to the best BDC stocks and best dividend growth stocks) typically pay non-qualified, ordinary-rate distributions — a 40.8% top combined rate once NIIT applies. These often make more sense inside an IRA or 401(k) than in a taxable account for investors above the threshold.
• Broad index ETFs (VOO, VTI-style funds) generate very little annual distributed income relative to their total return, deferring most of the tax hit — including NIIT — until shares are actually sold, which itself can be timed.
• Actively managed mutual funds can force out capital gains distributions in years you didn't sell anything and didn't want the income, creating NIIT exposure with no control over timing — a common, underappreciated cost of holding active funds in a taxable account.
• A large single-stock sale (concentrated employer stock, a legacy holding) behaves like the founder scenario above: consider spreading the sale across multiple tax years, or pairing it with tax-loss harvesting on other positions, to keep MAGI from spiking in one year.

Strategies to Reduce NIIT Exposure

• Shift taxable interest into municipal bonds — muni interest is excluded from NII entirely, reducing both your regular tax and your NIIT base
• Max out tax-deferred accounts (401k, traditional IRA, HSA) — contributions lower MAGI directly, and growth inside the account isn't NII until withdrawn as ordinary income (which itself is excluded from NII)
• Use tax-loss harvesting to offset realized gains — every dollar of loss that offsets a gain reduces both the gain itself and the NII it would have generated
• Favor broad index ETFs over actively managed mutual funds in taxable accounts — fewer forced capital gains distributions means less unplanned NII
• Locate REITs, BDCs, and other ordinary-income holdings in tax-advantaged accounts, and keep qualified-dividend stocks and low-turnover index funds in your taxable account — a form of asset location that reduces both ordinary tax and NIIT drag
• Time large gains (Roth conversions, business sales, concentrated stock sales) across multiple tax years to avoid single-year MAGI spikes over the threshold
• Consider qualified charitable distributions (QCDs) from an IRA if you're 70½+ — QCDs satisfy RMDs without raising MAGI the way a taxable withdrawal would
• For real estate investors: material participation (real estate professional status) can convert rental income and gains from passive (NII) to active (not NII) — a high bar, but valuable if you qualify

Frequently Asked Questions

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