You got a tax bill bigger than expected. You looked for the mistake and found none. The return was correct. What you may have hit is a surcharge that does not announce itself: the net investment income tax.

What it is

Under IRC §1411, the net investment income tax adds 3.8 percent on top of your regular tax on investment income, once your modified adjusted gross income passes $250,000 for joint filers, $200,000 single, or $125,000 married filing separately. It applies to the lesser of your net investment income or the amount your MAGI exceeds the threshold.

Net investment income means interest, dividends, capital gains, rental income, royalties, and passive business income. Wages are not investment income, but they count toward the MAGI that pushes you over the line. So a high salary can put your investment income into the tax even if the salary itself is not subject to it.

The part nobody mentions

Here is the quiet design feature: those thresholds have not changed since the tax took effect in 2013. They are not indexed for inflation.

Every year, raises, portfolio growth, and rising rents push more households over a line that has stayed frozen for more than a decade. A dual-income Northern Virginia couple who sat comfortably under the threshold a few years ago may be over it now with no change in how they earn or invest. The tax did not find them. The frozen threshold did. This is bracket creep, working exactly as a fixed threshold does in an inflationary decade.

What it stacks on

The 3.8 percent rarely arrives alone. For a high earner it rides on top of the 20 percent long-term capital gains rate, making the real top rate on investment gains 23.8 percent. On a rental sale, it can layer onto depreciation recapture as well. People budget for the headline rate and forget the surcharge sitting above it.

If you are selling property, this interacts directly with depreciation recapture, which is its own surprise.

What you can do

The 3.8 percent is plannable, but only before the income lands. Most of the work is managing MAGI and timing income:

• Retirement contributions and other above-the-line items that lower MAGI
• Harvesting losses to reduce net investment income
• Spreading large gains across tax years rather than realizing them in one
• For rental owners, the material participation and real estate professional rules that can move rental income out of the NIIT base

Each is fact-specific and timing-sensitive. The principle is the one that runs through all high-income work: decisions made during the year change the outcome; decisions made at filing only describe it. See our overview of tax planning for high-income earners for how the pieces fit together.

Want this reviewed against your own numbers? Schedule a discovery call at intake.simonsgroup.net to start a focused conversation.

Frequently asked questions

What income triggers the 3.8 percent net investment income tax?

Investment income (interest, dividends, capital gains, rental income, royalties, and passive income) once your MAGI exceeds $250,000 joint, $200,000 single, or $125,000 married filing separately. It applies to the lesser of your net investment income or the excess over the threshold.

Are the NIIT thresholds adjusted for inflation?

No. They have been fixed since 2013, which is why more taxpayers cross them each year as incomes rise.

Do my wages count?

Wages are not investment income and are not directly taxed by the NIIT, but they count toward the MAGI that determines whether your investment income is taxed.