The 3.8% Net Investment Income Tax in 2026: The Surtax That Quietly Taxes Your Gains

The Surtax Hiding in Plain Sight

Everyone knows the long-term capital gains rates: 0%, 15%, 20%. Clean, famous, quotable. And for high earners, quietly wrong — because there's a fourth number nobody puts on the chart, and it's 3.8%.

It's called the Net Investment Income Tax, it lives in Section 1411 of the code, and it's the reason a wealthy investor's "20% rate" is actually 23.8%. It rode in with the Affordable Care Act in 2010, switched on in 2013, and has been silently widening its reach ever since — not because the rate changed, but because the income line that triggers it has been frozen in place for over a decade while everyone's income drifted up toward it.

If you've got investment income and a decent salary, this is the surtax most likely to surprise you on a return. So let's pull it into the open.

§ 01How the 3.8% Actually Calculates

The NIIT is not simply 3.8% of your investment income. It's 3.8% of the smaller of two numbers, and that "lesser-of" rule is the whole game:

• Your net investment income for the year, or
• The amount your modified adjusted gross income (MAGI) exceeds the threshold for your filing status.

Whichever is smaller gets the 3.8%. Two examples make it click.

Case one. You're single, MAGI of $260,000, and $40,000 of that is investment income. Your MAGI clears the $200,000 line by $60,000. The smaller of ($40,000 income) and ($60,000 over the line) is $40,000. So you owe 3.8% × $40,000 = $1,520.

Case two. Same $40,000 of investment income, but now your MAGI is only $210,000. You're just $10,000 over the threshold. The smaller of ($40,000) and ($10,000) is $10,000. You owe 3.8% × $10,000 = $380. Same investments, a quarter of the tax — because the surtax can only reach the income that sits above the line.

That's the lever, and we'll come back to it: you can beat the NIIT by lowering your investment income or your MAGI. You don't have to win on both.

§ 02What Counts (and What Doesn't)

The label "investment income" is broader than dividends and narrower than "everything." Here's the actual map.

Caught by the NIIT: interest, dividends (qualified and ordinary), capital gains — including the gain on selling stocks, funds, crypto, and investment real estate — rental and royalty income, non-qualified annuity income, and income from businesses you're a passive investor in rather than actively running. The taxable overflow above your home-sale exclusion counts too.

Walks free: wages and salary, self-employment income, income from a business you materially participate in, Social Security benefits, distributions from 401(k)s, IRAs, and other qualified retirement plans, tax-exempt municipal bond interest, and any gain you exclude under Section 121 on your primary home.

That last point is the trap nobody sees coming. Retirement-plan distributions and Roth conversions aren't investment income, so they're never directly hit. But they raise your MAGI — and a higher MAGI means more of your dividends and gains poke above the threshold. The NIIT punishes you sideways.

§ 03The Threshold That Never Moves

Here's the quiet scandal of this tax. The trigger lines are:

Notice anything? They're not "2026 thresholds." They're the same numbers that took effect in 2013. The brackets index every year. The standard deduction indexes. The NIIT thresholds were written into statute with no inflation adjustment, and Congress has left them there for thirteen years and counting.

The math of that is relentless. A $200,000 single earner in 2013 was solidly upper-income. After a decade-plus of wage growth and inflation, $200,000 is increasingly a senior engineer, a two-physician marriage filing jointly at $250,000, a successful tradesperson. Each year, the freeze quietly pulls more of the upper-middle class into a tax that was sold as hitting "the wealthy." It's bracket creep, just on a line that was never supposed to creep.

And the married-filing-separately number is brutal on purpose — $125,000 each, with none of the planning flexibility a joint return gives you. Couples who split for other reasons sometimes walk straight into it.

§ 04The Real Top Rate Is 23.8%

Stack the pieces and the famous "20% capital gains rate" disappears. For a top-bracket investor:

Then add your state. In California, that 23.8% federal on a long-term gain becomes something north of 37% all-in. This is exactly why holding for the long term matters so much: the gap between 23.8% and 40.8% is the gap between long- and short-term, and it's enormous at scale.

One clean-up point people get wrong: the NIIT is not the same as the 0.9% Additional Medicare Tax. That 0.9% is the wage-and-self-employment cousin — it hits earned income over the same thresholds. The NIIT hits investment income. You can owe both in the same year, but never on the same dollar. One taxes what you earn working; the other taxes what your money earns sitting still.

§ 05Why Trusts Get Hammered

If you manage a trust, the NIIT is far nastier than it is for individuals. A trust or estate pays the 3.8% on the lesser of its undistributed net investment income or the amount its adjusted gross income exceeds the top trust bracket — which in 2026 starts at roughly $16,000.

Read that again. An individual gets a $200,000 cushion. A trust gets about $16,000. Trusts hit the top of every rate schedule at a level of income that wouldn't even register for a person, and the NIIT is no exception. A trust with $100,000 of retained investment income is paying the full surtax on nearly all of it.

The standard fix is distribution: push the income out to beneficiaries who have their own $200,000-plus thresholds, and the surtax often shrinks or vanishes. It's the single biggest reason trustees watch the year-end distribution decision so closely.

§ 06How to Legally Stay Under It

Because the tax keys off the lesser of two numbers, you've got two doors to work. Lower your investment income, or lower your MAGI — either one caps the damage. The practical moves:

• Harvest losses. Realized capital losses reduce net investment income directly. See tax-loss harvesting — and mind the wash sale rule while you do it.
• Hold municipal bonds. Their interest is excluded from net investment income entirely — and from regular income tax. For a high earner near the line, muni yield can beat a higher taxable yield after the surtax.
• Max pre-tax retirement contributions. 401(k) and traditional IRA deferrals lower your MAGI, pulling you back under the threshold.
• Spread big gains across years. An installment sale on a property or business splits one giant gain into smaller annual slices, each one poking less above the line. So does simply not realizing everything in one tax year.
• Time Roth conversions. Conversions spike MAGI. Do them in lower-income years, or in chunks, so they don't drag your investment income into the surtax.
• Use the home-sale exclusion fully. The gain you exclude under Section 121 never enters the NIIT calculation. Reconstruct your basis so more of the gain stays excluded.

Want to see the surtax land on a specific gain? The capital gains calculator has an optional exact-MAGI field that computes the NIIT alongside the federal and state pieces.

§ 07Key Takeaways

The NIIT is 3.8% on the lesser of your net investment income or your MAGI over the threshold. Beat either number and you shrink the tax.

Thresholds are $200k single, $250k married, $125k MFS — frozen since 2013. Every year the freeze pulls more upper-middle earners in.

The real top capital gains rate is 23.8% federal, not 20% — and 40.8% on short-term gains, before state tax.

Trusts pay it above roughly $16,000. Distributing income to beneficiaries is the usual escape.

For the rates underneath the surtax, read the 2026 capital gains guide, then run your own numbers in the calculator.

Sources: IRC §1411 (Net Investment Income Tax); IRS Form 8960 and instructions; IRS Rev. Proc. 2025-32 (2026 long-term capital gains breakpoints and trust brackets); Affordable Care Act (NIIT enacted 2010, effective 2013). This is general information, not tax advice.