The 3.8% surcharge on capital gains tax is the Net Investment Income Tax, an extra federal levy that stacks on top of your regular capital gains rate once your modified adjusted gross income crosses $200,000 for single filers or $250,000 for married couples filing jointly.1Internal Revenue Service. Questions and Answers on the Net Investment Income Tax Because it stacks, the top federal rate on long-term gains reaches 23.8% rather than the 20% figure most people know. The surcharge was created by the Health Care and Education Reconciliation Act of 2010 and lives at 26 U.S.C. § 1411.2Office of the Law Revision Counsel. 26 U.S. Code 1411 – Imposition of Tax It’s often called a Medicare surtax, but the revenue goes to the U.S. General Fund.
Who Owes the Surcharge
The trigger is your modified adjusted gross income, not just your investment earnings. MAGI includes wages, business income, retirement distributions, and investment income together. The statutory thresholds are:1Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
- Married filing jointly or qualifying surviving spouse: $250,000
- Single or head of household: $200,000
- Married filing separately: $125,000
These numbers have never been indexed for inflation. They’ve held at the same dollar amounts since 2013, so wage growth and rising asset values pull more households into the surcharge every year. A salary of $180,000 plus a $30,000 stock gain now puts a single filer above $200,000 and into NIIT territory.
What Income the 3.8% Applies To
Net investment income covers a broad slice of what you earn from assets: capital gains from selling stocks, bonds, mutual funds, and investment real estate, plus interest, dividends, annuity income, royalties, and rents.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax Passive business income counts too, so a limited partnership interest or a rental property you don’t actively manage feeds the calculation.2Office of the Law Revision Counsel. 26 U.S. Code 1411 – Imposition of Tax
Several kinds of income are carved out:
- Tax-exempt interest, such as interest from municipal bonds.3Internal Revenue Service. Topic No. 559, Net Investment Income Tax
- Distributions from 401(k)s, IRAs, 403(b)s, and other qualified retirement plans.1Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
- Active business income where you materially participate in the trade or business.
- Wages and self-employment income, which are subject to payroll taxes instead.
The passive-versus-active line trips up more people than any other part of the rule. Own a rental and hire a manager, and the rent is passive income that counts. Qualify as a real estate professional who materially participates, and the same rent may fall outside the NIIT. The classification turns on your involvement, not the asset.
How the Surcharge Is Calculated
The 3.8% applies to the smaller of two figures: your net investment income for the year, or the amount by which your MAGI exceeds your filing threshold.4Internal Revenue Service. Instructions for Form 8960 The tax can never exceed either number.
Say you’re a single filer with $230,000 MAGI, and $50,000 of it is net investment income. Your MAGI is $30,000 over the $200,000 threshold. Because $30,000 is less than the $50,000 in investment income, the 3.8% applies to $30,000, producing $1,140 in NIIT.
Change the facts. Same $230,000 MAGI, but only $12,000 of net investment income. The threshold excess is still $30,000, but the investment income is smaller. The tax applies to $12,000, producing $456.
You report and calculate the surcharge on Form 8960, filed with your regular 1040.5Internal Revenue Service. Form 8960 – Net Investment Income Tax – Individuals, Estates, and Trusts You can reduce net investment income by properly allocable deductions such as investment interest, margin interest, and rental property expenses. Personal deductions like home mortgage interest or charitable contributions don’t reduce it.
How It Stacks on Capital Gains Rates
Long-term capital gains from assets held more than a year are taxed at 0%, 15%, or 20% depending on your taxable income and filing status.6Internal Revenue Service. Topic No. 409, Capital Gains and Losses Short-term gains, from assets held a year or less, are taxed at your ordinary income rate, which can reach 37%. The NIIT sits on top of whichever rate you owe.
That layering is where the real surprise comes in. A taxpayer in the 15% long-term bracket whose overall income is high enough to trigger the NIIT pays an effective 18.8%. A taxpayer in the 20% bracket pays 23.8%. Short-term gains for a high earner can face ordinary rates plus 3.8% on top.
Home Sales and the Surcharge
Selling your primary residence can pull the NIIT into the picture, but only above the Section 121 exclusion. Under 26 U.S.C. § 121, single filers can exclude up to $250,000 of gain, and married couples filing jointly up to $500,000, if you owned and lived in the home for at least two of the five years before the sale.7Office of the Law Revision Counsel. 26 USC 121 – Exclusion of Gain From Sale of Principal Residence
Excluded gain is not net investment income. Gain above the exclusion is. If a married couple realizes a $700,000 gain on their home, $500,000 is excluded and $200,000 enters the NIIT calculation. Whether they actually owe 3.8% depends on whether their MAGI for that year clears $250,000, which a sale of that size usually pushes them past.
Vacation homes and investment properties don’t qualify for the Section 121 exclusion, so the entire gain counts as net investment income. Selling a second home or a long-held rental is where the stacking hurts most: 20% capital gains plus 3.8% NIIT sends nearly a quarter of the profit to federal tax before any state tax.
Trusts and Estates Face a Much Lower Threshold
If your investments are held through a trust or an estate, the surcharge applies at a far lower income level. Instead of $200,000 or $250,000, trusts and estates become subject to the 3.8% once their adjusted gross income exceeds the point where the top trust bracket begins, roughly $16,000 for 2026.4Internal Revenue Service. Instructions for Form 8960 Most trusts holding investments will owe some NIIT on undistributed investment income.
The 3.8% applies to the lesser of the trust’s undistributed net investment income or the excess of its AGI over that threshold. Income distributed to beneficiaries is taxed at the beneficiary level under the individual thresholds instead. That difference gives trustees a strong reason to distribute investment income rather than let it accumulate. Charitable trusts, grantor trusts, and perpetual care trusts are exempt at the trust level, though grantor trust income still runs through the grantor’s personal return for NIIT purposes.
Estimated Payments and Underpayment Penalties
The NIIT is treated like any other income tax for estimated payment purposes, so it needs to be built into your quarterly payments.1Internal Revenue Service. Questions and Answers on the Net Investment Income Tax Selling a large position in March and not adjusting your payments can leave you with an underpayment penalty at filing.
The penalty is based on how much you underpaid and how long the shortfall sat, using the IRS’s quarterly interest rates.8Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty The standard safe harbor still works: pay at least 110% of your prior year’s tax liability through withholding and estimated payments (100% if your prior-year AGI was under $150,000), and you generally avoid the penalty.
This trips up people most often in years with a one-time event such as selling a business, exercising stock options, or unloading a rental. Withholding that covers a normal year won’t cover a large NIIT bill layered on top of a large capital gains bill. After any major sale, run the numbers and make an estimated payment in the same quarter.