What Is NIIT? Net Investment Income Tax Explained
For informational purposes only, not financial advice. Full disclaimer
NIIT stands for Net Investment Income Tax. It is a separate 3.8% federal surtax that can apply when higher-income taxpayers earn investment income such as capital gains, dividends, interest, rental income, and some passive business income.
According to IRS Tax Topic No. 559, NIIT generally applies to the lesser of your net investment income or the amount your modified adjusted gross income (MAGI) exceeds the applicable threshold. That is why not every dollar of investment income is always hit with the surtax.
Use the capital gains calculator to estimate your regular federal gain tax first, then layer NIIT on top if your income crosses the threshold.
Try the Capital Gains Tax CalculatorNIIT Formula
NIIT = 3.8% x lesser of (Net Investment Income) or (MAGI - NIIT threshold)- Single or head of household: threshold is $200,000
- Married filing jointly or qualifying surviving spouse: threshold is $250,000
- Married filing separately: threshold is $125,000
These NIIT thresholds are separate from the ordinary income tax brackets. A taxpayer can be below the top ordinary income bracket and still owe NIIT if enough investment income pushes MAGI over the threshold.
Example Calculation
A single filer has $180,000 of wages and realizes an $80,000 long-term capital gain. MAGI is $260,000.
- MAGI: $260,000
- Single filer NIIT threshold: $200,000
- Excess MAGI over threshold: $260,000 - $200,000 = $60,000
- Net investment income from the sale: $80,000
- Lesser amount: $60,000
- NIIT: $60,000 x 3.8% = $2,280
The taxpayer owes $2,280 of NIIT in addition to any regular long-term capital gains tax. NIIT is not automatically charged on the full $80,000 gain just because the gain exists.
What Counts as Net Investment Income?
- Taxable interest
- Ordinary and qualified dividends
- Capital gains from stocks, funds, ETFs, and many other assets
- Rental and royalty income, unless excluded by an active-business exception
- Passive business income from activities in which you do not materially participate
Wages, unemployment compensation, Social Security benefits, active self-employment income, and distributions from many retirement accounts do not generally count as net investment income for NIIT. The Instructions for Form 8960 walk through the detailed inclusions and exclusions.
How NIIT Interacts With Capital Gains
NIIT often surprises investors after a large stock sale, mutual fund distribution, rental-property sale, or business exit. Regular capital gains tax and NIIT are separate layers. A long-term gain can be taxed at 15% or 20%, and then some or all of that same gain may also trigger the extra 3.8% surtax.
This is one reason high-income investors sometimes talk about a 23.8% federal long-term capital gains rate. That number is the 20% long-term capital gains rate plus 3.8% NIIT when the thresholds are exceeded and the full gain is exposed to NIIT.
Common NIIT Planning Levers
- Harvest capital losses to offset realized gains.
- Use tax-advantaged accounts where investment growth is sheltered from annual capital gains tax.
- Spread realizations across tax years when possible instead of stacking all gains into one sale year.
- Coordinate bonus income, stock sales, and business income so MAGI does not unexpectedly jump above the threshold.
Most investors get a cleaner estimate by calculating regular capital gains tax first and then checking whether NIIT applies based on total income.
NIIT matters most in years with unusually high investment income. If you are selling appreciated assets, exercising concentrated positions, or closing a large business transaction, this surtax can materially change the after-tax result.
Frequently Asked Questions
What does NIIT stand for?+
What is the NIIT threshold?+
Does NIIT apply to wages?+
Does NIIT apply to capital gains?+
Is NIIT the same as capital gains tax?+
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Disclaimer: This article is for informational purposes only and does not constitute financial advice. Consult a qualified financial advisor for decisions about your specific situation.