Tax planning
Net Investment Income Tax: The 3.8% Surtax That Surprises High-Earning Business Owners
The 3.8% Net Investment Income Tax (NIIT) applies to investment income for individuals above $200,000 in modified AGI. It's on top of regular income tax and capital gains rates — and it applies to passive business income, rental income, and gains on selling a business.
Written by Matt Reese, CPA · 6 min read · Published April 2026·Share on LinkedIn
Key Takeaways
- The 3.8% NIIT applies to the lesser of: (1) your net investment income, or (2) your MAGI above the threshold ($200,000 for single filers, $250,000 for married filing jointly).
- Net investment income includes interest, dividends, capital gains, rental income, and income from passive activities — including passive S-corp or partnership income.
- Active business income that is not passive is generally not subject to NIIT. An S-corp owner who materially participates avoids NIIT on the business income. A passive investor in an S-corp does not.
- Gains from selling a business or its assets can trigger NIIT, particularly when selling a passive interest or when the transaction includes assets that generate investment income.
What is the Net Investment Income Tax
The Net Investment Income Tax (NIIT) was enacted as part of the Affordable Care Act in 2013. It imposes an additional 3.8% tax on investment income for individuals whose modified adjusted gross income (MAGI) exceeds threshold amounts:
- $200,000 for single filers and head of household
- $250,000 for married filing jointly
- $125,000 for married filing separately
The NIIT thresholds are not indexed for inflation — they have remained the same since 2013. As incomes have risen, more taxpayers have been pulled above the threshold.
NIIT is the difference between a 20% capital gains rate and a 23.8% capital gains rate for high earners — and it applies to gains from selling a business, rental income, and passive business interest.
The calculation: what triggers NIIT
The NIIT is 3.8% on the lesser of: (1) Net investment income, or (2) The excess of MAGI over the applicable threshold.
The NIIT is calculated on the lesser of the two amounts. If NII is smaller than the MAGI excess, NIIT applies to the full NII. If NII is larger, only the MAGI excess gets taxed. The result: reducing NII directly reduces NIIT, as does reducing MAGI below the threshold.
What is and isn’t net investment income
| Income type | Subject to NIIT? | Notes |
|---|---|---|
| Interest income (taxable bonds, bank accounts) | Yes | |
| Dividends (ordinary and qualified) | Yes | Qualified dividends face lower regular rate but still + 3.8% NIIT |
| Capital gains (stocks, real estate, business) | Yes | Long-term gains: 20% + 3.8% = 23.8% federal for top earners |
| Rental income (passive) | Yes | Most individual landlords have passive rental income |
| Passive S-corp/partnership income | Yes | Owner doesn't materially participate |
| Royalties from passive activity | Yes | |
| Active business income (S-corp, partnership) | No | Must materially participate |
| Wages and self-employment income | No | Subject to income tax and FICA/SE tax instead |
| IRA and 401(k) distributions | No | But increases MAGI, potentially exposing other NII |
| Municipal bond interest | No | Tax-exempt at federal level; not NII |
| Social Security benefits | No | |
| Alimony (for agreements before 2019) | No | Gross income but not NII |
NIIT on selling a business
Selling a business or its assets often triggers NIIT — one of the less-discussed components of the business sale tax bill:
- Asset sale: Gains on each asset category (goodwill, equipment, real estate) are generally investment income and subject to NIIT if you’re above the threshold.
- S-corp stock sale: Gain on sale of S-corp stock is a capital gain — and is subject to NIIT.
- Active participation exception: If you materially participated in the business for most of the 5 years preceding the sale, some or all of the gain from selling your interest in an S-corp or partnership may not be subject to NIIT. This is a complex area with specific rules under Treasury regulations.
| Scenario | Federal capital gains rate | NIIT | Combined federal rate |
|---|---|---|---|
| Long-term gain, income below threshold | 15% | 0% | 15% |
| Long-term gain, income above threshold (under $553k) | 20% | 3.8% | 23.8% |
| Short-term gain (held less than 1 year) | 37% (ordinary income) | 3.8% | 40.8% |
| Plus California state tax (if applicable) | +13.3% | N/A | 37.1% (long-term) or 54.1% (short-term) |
Business sellers often underestimate the NIIT impact
Material participation: the key to avoiding NIIT on business income
The most common way active business owners avoid NIIT on their business income is through material participation. If you materially participate in an S-corp or partnership, your share of ordinary income is not passive and not subject to NIIT.
The IRS provides seven tests for material participation — meeting any one qualifies:
- More than 500 hours in the activity during the year (most common for working owners)
- Your participation is substantially all of the participation of all individuals (including non-owners)
- More than 100 hours and at least as much as any other individual
- The activity is a significant participation activity and total hours in all significant participation activities exceeds 500
- Material participation in any 5 of the prior 10 years
- Material participation for any 3 prior years (for personal service activities)
- Based on all the facts and circumstances, you participated on a regular, continuous, and substantial basis
Document your participation hours
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Frequently asked
Questions owners actually ask
- Does the NIIT apply to S-corp income?
- It depends on whether you materially participate in the S-corp. If you work in the business and meet the material participation tests, your share of S-corp ordinary income is not passive and is not subject to NIIT. If you're a passive investor — you own S-corp stock but don't work in the business — your share of income is passive and is subject to NIIT. The distinction is the same one that determines whether losses are passive.
- Is my rental income subject to NIIT?
- Generally yes — rental income is passive activity income for most landlords. The exception is real estate professionals who qualify under the 750-hour test and materially participate in each rental property. For most business owners with a few rental properties on the side, the rental income is passive and adds to the NIIT base.
- When I sell my business, will I owe NIIT on the gain?
- Potentially yes, if the gain pushes your MAGI above the threshold. For an asset sale, the gain flows through like capital gain and is included in net investment income (subject to NIIT). For an S-corp stock sale, the gain is investment income and is subject to NIIT. This is one reason the tax bill on a business sale is higher than people expect — capital gains rate + NIIT + state tax can exceed 30% in California.
- Does NIIT apply to retirement account withdrawals?
- No — distributions from traditional IRAs, 401(k)s, and other qualified plans are not investment income for NIIT purposes. Roth distributions are also not subject to NIIT. However, IRA and 401(k) distributions increase your MAGI, which can push other investment income above the threshold. So while the withdrawal itself isn't NIIT income, it can cause more of your other investment income to be taxed at 3.8%.
- Is there any way to reduce NIIT?
- There are a few legitimate strategies: (1) Increase material participation to convert passive income to non-passive. (2) Move taxable investments into retirement accounts where the income isn't NII. (3) Use tax-exempt bonds — interest on municipal bonds isn't NII. (4) Harvest capital losses to offset capital gains. (5) For business owners near the threshold, timing income into a lower-income year can keep MAGI below the threshold. All of these require coordination between your CPA and financial advisor.
Take the next step
Turn tax questions into a plan. Talk with Matt or see how we work with operating business owners.
Educational content only.This article is for informational purposes and does not constitute tax, legal, or investment advice. Every owner’s facts are different; consult a qualified CPA and advisor before acting. Tax and accounting services are provided through Matt Reese, CPA; investment advisory services are provided through Measured Risk Portfolios, a registered investment adviser. Matt Reese, CPA and Measured Risk Portfolios are separate entities; clients are not required to engage both.