Key Takeaways
The Net Investment Income Tax is a 3.8% surtax that many investors with higher incomes pay in addition to ordinary capital gains tax, yet it is widely misunderstood — both in terms of who actually owes it and how to reduce exposure to it. Understanding the formula, the thresholds, and the exclusions is the prerequisite for any serious tax-efficiency strategy around investment income.
Direct answer: The NIIT is a 3.8% federal surtax on net investment income for individuals whose MAGI exceeds $200,000 (single) or $250,000 (married filing jointly). It applies to the lesser of your net investment income or the amount your MAGI exceeds the threshold — not to all investment income. These thresholds have not been adjusted for inflation since 2013. The tax is reported on Form 8960 and flows to Form 1040. Capital gains, dividends, interest, rents, and passive business income count as NII; wages, Social Security, and IRA/401(k) distributions do not.
- The NIIT rate is a flat 3.8%, making the combined top federal rate on long-term capital gains 23.8% (20% + 3.8%) and potentially 40.8% on short-term gains (37% + 3.8%).
- NIIT thresholds ($200k single, $250k MFJ) have been fixed since 2013 and are not indexed for inflation — bracket creep is real.
- IRA and 401(k) distributions do not count as net investment income but do raise MAGI, which can pull more other investment income into NIIT territory.
- The NIIT is accompanied by a separate 0.9% Additional Medicare Tax on wages and self-employment income above the same thresholds — the two taxes use the same income trigger but apply to different income types.
- Tax-loss harvesting, Roth conversions, installment sales, qualified opportunity zone investments, and real estate professional status are the most-used tools for reducing NIIT exposure.
Background: What the NIIT Is and Where It Came From
The Net Investment Income Tax was enacted as part of the Health Care and Education Reconciliation Act of 2010, one of the statutes that together make up the Affordable Care Act (ACA). It is codified at Internal Revenue Code Section 1411 and took effect for tax years beginning on or after January 1, 2013. The revenue it generates funds Medicare — it is formally titled the "unearned income Medicare contribution tax" in the IRS regulations — though the amount does not flow into the Medicare trust fund in the same way payroll taxes do.
Congress chose a flat rate (3.8%) and fixed income thresholds rather than a graduated structure, and deliberately declined to index those thresholds to inflation. The result is that the real income level at which the NIIT kicks in has declined steadily since 2013 as nominal incomes have risen. A filer at exactly the threshold in 2013 had meaningful real purchasing power; in 2026, that same $200,000 is worth roughly 30% less in real terms, meaning a taxpayer whose real income has not increased at all could now owe the NIIT simply because nominal wages and portfolio values rose with general price levels. This is one of the reasons NIIT exposure is more common today than it was at inception.
The NIIT Formula: Lesser-Of Calculation
The NIIT applies to the lesser of two amounts:
- Your net investment income (NII) for the tax year, or
- The amount by which your MAGI exceeds the applicable threshold for your filing status.
The tax is then 3.8% of whichever is smaller. This lesser-of design means the NIIT does not necessarily apply to all of your investment income — it is limited by how far above the threshold your income sits. A filer with large NII but MAGI only slightly above the threshold will owe NIIT only on the excess over the threshold, not on all of their investment income.
Filing status thresholds (2026)
| Filing Status | MAGI Threshold | Inflation-Indexed? |
|---|---|---|
| Single | $200,000 | No — unchanged since 2013 |
| Married Filing Jointly (MFJ) | $250,000 | No — unchanged since 2013 |
| Married Filing Separately (MFS) | $125,000 | No — unchanged since 2013 |
| Head of Household | $200,000 | No — unchanged since 2013 |
| Qualifying Surviving Spouse | $250,000 | No — unchanged since 2013 |
Source: IRC §1411; IRS Publication 550 (2025). Thresholds confirmed unchanged for 2026.
MAGI for NIIT purposes
For most taxpayers, modified adjusted gross income (MAGI) for NIIT purposes equals regular AGI plus any foreign income excluded under IRC §911. For nearly all U.S. residents without foreign income, MAGI equals AGI from the front page of Form 1040. MAGI includes wages, salaries, retirement distributions, capital gains, dividends, interest, and Social Security income — the full income picture before most deductions — which is why it can exceed the NIIT threshold even for taxpayers with modest investment portfolios.
What Counts as Net Investment Income
NII is defined in IRC §1411(c) and the final Treasury regulations (Treas. Reg. §1.1411-4). It covers three broad categories of passive or portfolio income, net of deductions allocable to that income.
Category 1: Passive income
- Interest — taxable interest from bank accounts, bonds, CDs, money market funds, and peer-to-peer lending (tax-exempt municipal bond interest is excluded).
- Dividends — both qualified dividends and ordinary dividends, whether from domestic stocks, foreign stocks held in a taxable account, or mutual funds.
- Annuity income — the taxable portion of annuity distributions, where income is not from a qualified retirement plan.
- Royalties — payments for use of intellectual property, mineral rights, or similar assets where the taxpayer does not materially participate in the related business.
- Rents — rental income net of deductible rental expenses, unless you are a real estate professional who meets the material participation tests of IRC §469(c)(7) (see Planning Strategies below).
Category 2: Capital gains from dispositions
- Short-term capital gains from sales of stocks, bonds, options, mutual funds, and other capital assets held one year or less.
- Long-term capital gains from assets held more than one year, including collectibles (taxed at up to 28% ordinarily).
- Capital gain distributions from mutual funds and ETFs reported on Form 1099-DIV.
- Gains on sale of a primary residence to the extent they exceed the available IRC §121 exclusion ($250,000 for single filers, $500,000 for MFJ). If you sell a home for a gain of $600,000 and qualify for the full $500,000 MFJ exclusion, the remaining $100,000 gain counts as NII.
- Gains from passive activities — any gain from selling property used in a passive trade or business.
Category 3: Passive trade or business income
Income from a trade or business that is a passive activity under the IRC §469 rules — meaning you invest in it but do not materially participate — counts as NII. This includes limited partnership income and S-corporation income from a company in which you hold a passive interest. Active business income, where you materially participate, is excluded.
What Is Excluded from the NIIT
Understanding what is not NII is just as important as knowing what is, both for calculating actual exposure and for identifying planning levers.
- Wages and salaries — earned income from employment is never NII, regardless of amount.
- Self-employment income — income from a trade or business you actively conduct is excluded (though it is subject to the separate 0.9% Additional Medicare Tax above the same thresholds).
- Active business income — income from any trade or business in which you materially participate is excluded, even if it flows through a partnership or S-corporation.
- Social Security benefits — the taxable portion of Social Security income is excluded from NII, though it is included in MAGI and can push you over the threshold.
- Pension and annuity income from qualified plans — distributions from defined benefit pension plans and annuities from qualified plans are excluded.
- IRA and 401(k) distributions — distributions from traditional IRAs, Roth IRAs (qualified distributions), 401(k) plans, 403(b) plans, and similar qualified retirement accounts are not NII. This is a critical planning point: a large IRA distribution does not directly trigger the NIIT, but it increases MAGI and can pull investment income that was below the threshold into NIIT territory.
- Tax-exempt interest — interest from qualifying municipal bonds is explicitly excluded from NII. However, it is included in MAGI, so it can still indirectly raise your exposure.
- Unemployment compensation — excluded from NII.
- Gain from sale of a primary residence up to the exclusion — the §121 exclusion removes the first $250,000 ($500,000 MFJ) of primary residence gain from NII entirely.
Practical checklist
- Run a pre-year-end MAGI estimate before taking any large distributions or realizing large gains.
- Remember that tax-exempt bond interest and IRA distributions both increase MAGI even though they are not NII — they can silently drag other income into NIIT range.
- If you own real estate, assess whether you qualify as a real estate professional — that status reclassifies rental income from passive (NII) to active (not NII).
How the NIIT Stacks on Top of Capital Gains Rates
The NIIT is additive. It does not replace the regular capital gains rate or the ordinary income rate on investment income; it piles on top of them. For investors above the threshold, this is what the combined federal tax picture looks like on investment income in 2026:
| Income Type | Regular Rate (top bracket) | NIIT | Combined Top Federal Rate |
|---|---|---|---|
| Long-term capital gains | 20% | 3.8% | 23.8% |
| Qualified dividends | 20% | 3.8% | 23.8% |
| Short-term capital gains | 37% (ordinary income) | 3.8% | 40.8% |
| Ordinary dividends | 37% (ordinary income) | 3.8% | 40.8% |
| Taxable interest | 37% (ordinary income) | 3.8% | 40.8% |
| Net rental income (passive) | 37% (ordinary income) | 3.8% | 40.8% |
State income taxes are additional and vary widely. California and New York City investors face combined marginal rates well above 50% on short-term gains.
The 23.8% combined top rate on long-term capital gains is significant not just in absolute terms but in comparison to alternatives. A taxpayer deciding between holding a position longer (to qualify for long-term treatment) versus selling now faces a 17-percentage-point spread between 23.8% and 40.8% on any gain above the NIIT threshold — one of the largest tax-rate wedges in the federal code for individuals.
Worked Example: Calculating Your NIIT
Illustrative example — for education only. Consult a tax professional for your specific situation.
Scenario
Alex and Jordan file jointly. Alex earns $210,000 in wages. Jordan earns $20,000 in wages. They also received $30,000 in qualified dividends, $15,000 in long-term capital gains from selling index fund shares, and $8,000 in interest income. They have no rental income and no passive business interests.
Step 1: Calculate total MAGI
- Wages: $210,000 + $20,000 = $230,000
- Qualified dividends: $30,000
- Long-term capital gains: $15,000
- Interest income: $8,000
- Total MAGI: $283,000
Step 2: Calculate net investment income
- Qualified dividends: $30,000
- Long-term capital gains: $15,000
- Interest income: $8,000
- Less deductible investment expenses: assume $0 for simplicity
- Total NII: $53,000
Step 3: Apply the lesser-of test
- MAGI ($283,000) minus MFJ threshold ($250,000) = $33,000 excess MAGI
- NII = $53,000
- Lesser of $53,000 and $33,000 = $33,000
Step 4: Calculate NIIT owed
$33,000 × 3.8% = $1,254
Even though Alex and Jordan have $53,000 in investment income, they only owe NIIT on the $33,000 portion that corresponds to their excess MAGI. If their wages were $20,000 lower (total MAGI $263,000), excess MAGI would be just $13,000, and they'd owe $494 in NIIT instead. This is why MAGI management matters as much as NII management.
Form 8960: Reporting the NIIT
The NIIT is calculated on Form 8960, Net Investment Income Tax — Individuals, Estates, and Trusts, which is attached to your Form 1040. The form has three parts:
- Part I (Lines 1–8): Gross investment income. Each category of NII — interest, dividends, annuity distributions, rents, royalties, passive income, capital gains — has its own line. Gains from Schedule D and gains from passive activities feed into this section.
- Part II (Lines 9–12): Deductions for investment expenses. Allocable deductions — investment interest expense from Schedule A, state and local income taxes allocable to NII (subject to the $10,000 SALT cap on Schedule A), miscellaneous investment expenses — are subtracted here to arrive at net investment income on Line 12.
- Part III (Lines 13–17): Tax computation. Line 13 is your MAGI from Form 1040. Line 14 is the applicable threshold for your filing status. Line 15 is the excess (Line 13 minus Line 14, if positive). Line 16 is the lesser of Line 12 (NII) or Line 15 (excess MAGI). Line 17 is the NIIT: 3.8% × Line 16, which flows to Schedule 2 of Form 1040 as an additional tax.
You are required to file Form 8960 if your MAGI exceeds the applicable threshold and you have net investment income. There is no estimated-tax safe harbor specific to the NIIT — it is subject to the same estimated-tax and withholding rules as regular income tax, and underpayment can trigger penalties.
The 0.9% Additional Medicare Tax: The NIIT's Companion
The Affordable Care Act created two distinct high-income surtaxes that share the same income thresholds but apply to completely different types of income. The NIIT (3.8%) applies to net investment income. The Additional Medicare Tax (AMT) — sometimes confusingly abbreviated the same way as the Alternative Minimum Tax — applies at 0.9% to wages, salaries, and self-employment income above the same thresholds.
The key distinctions:
- Rate: The Additional Medicare Tax is 0.9%, less than half the NIIT rate.
- Income type: It applies to earned income (wages, tips, Railroad Retirement Board benefits, and net self-employment income) — precisely the income types excluded from the NIIT.
- Withholding mechanics: Employers are required to withhold the Additional Medicare Tax on wages above $200,000 per employee (not per household), which means a married couple where each spouse earns under $200,000 individually may owe additional tax on their combined wages above $250,000 even though no Additional Medicare Tax was withheld from either paycheck. Checking for under-withholding at filing is important.
- Form: The Additional Medicare Tax is also calculated on Form 8959 (not 8960) and flows to Form 1040 Schedule 2.
A high-income investor may owe both: NIIT on investment income and Additional Medicare Tax on earned income, in the same year, because of the same threshold. The two surtaxes are independent — neither one reduces or offsets the other — but they are reported on different forms and should not be conflated.
Planning Strategies to Reduce NIIT Exposure
NIIT planning operates on two levers: reduce net investment income (so the NII portion of the lesser-of test is smaller) or reduce MAGI (so the excess-MAGI portion is smaller, or the threshold is not crossed at all). The best strategies depend on which lever is binding in your situation.
1. Tax-loss harvesting
Realized capital losses offset realized capital gains dollar-for-dollar. If you have $50,000 in gains and $20,000 in losses, your NII from capital gains is $30,000, not $50,000 — directly reducing the amount subject to NIIT. Losses can also be carried forward to offset future gains. The wash-sale rule (IRC §1091) prohibits repurchasing a substantially identical security within 30 days before or after the sale, but you can immediately buy a similar-but-not-identical replacement to maintain market exposure.
2. Timing of large gain events
If a large capital gain event (selling a business, real estate, or concentrated stock position) can be planned, MAGI management across tax years matters. Recognizing a $500,000 gain in one year produces far more NIIT than spreading it or timing it to a lower-income year (early retirement, a sabbatical, a year with large deductions). Installment sales under IRC §453 allow gain from asset sales to be recognized ratably over several years as payments are received, potentially keeping MAGI below or closer to the threshold in each year.
3. Roth IRA conversions in low-income years
Traditional IRA distributions (required minimum distributions and voluntary withdrawals) are not NII, but they increase MAGI. A large RMD in a year with significant investment income can be the difference between paying NIIT on all of your investment income or none of it. Converting traditional IRA balances to Roth IRA in years when MAGI is below the threshold eliminates future RMDs that would otherwise raise MAGI. The conversion itself raises MAGI in the year it occurs, so the timing requires careful modeling.
4. Qualified Opportunity Zone investments
Investing capital gains in a Qualified Opportunity Fund (QOF) under IRC §1400Z-2 defers recognition of those gains until the earlier of the date the QOF investment is sold or December 31, 2026. For gains deferred past that date under prior law, only the gain on the QOF investment itself remains, and any gain from a QOF investment held at least 10 years is excluded from gross income entirely. This can reduce both NII and MAGI in the year of the original gain event, though the deferral itself eventually triggers NIIT in the year the gain is recognized.
5. Municipal bonds for interest income
Interest from qualifying municipal bonds is excluded from NII and from regular income tax. For investors in high brackets who need fixed-income exposure, munis can effectively yield more on an after-tax basis than taxable bonds once the NIIT saving is included. At a combined 40.8% marginal rate on taxable interest, a muni yielding 3.5% is equivalent to a taxable bond yielding nearly 5.9%.
6. Maximizing tax-deferred retirement contributions
Contributions to 401(k), 403(b), SIMPLE IRA, SEP-IRA, and similar plans reduce AGI directly, which reduces MAGI. A sole proprietor who can contribute $69,000 (2024 combined limit) to a SEP-IRA could reduce MAGI enough to fall below or closer to the NIIT threshold, entirely on the earned-income side of the ledger without touching the investment portfolio.
7. Real estate professional status
Under IRC §469(c)(7), a taxpayer qualifies as a real estate professional if (a) more than half of their personal services during the year are in real property trades or businesses in which they materially participate, and (b) they perform more than 750 hours of services in those activities during the year. If you qualify, rental activities in which you materially participate are reclassified from passive to active, removing rental income from NII entirely. This is a significant benefit for investors with substantial rental income, but the qualification requirements are strict and heavily scrutinized by the IRS.
Practical checklist
- Run a mid-year MAGI projection by June or July to see whether you are likely to owe NIIT and by how much.
- Identify any loss positions that can be harvested to offset realized gains before year-end.
- If MAGI is close to the threshold and you have flexibility, consider deferring income to January or accelerating deductions into the current year.
- Model Roth conversions against the NIIT threshold every few years to decide whether the conversion MAGI cost is worth the future RMD reduction.
- Review installment-sale structures with a tax advisor before closing any large asset sale.
Misconceptions vs. Reality
| Misconception | Reality |
|---|---|
| The NIIT applies to all investment income once you cross the threshold | It applies only to the lesser of your NII or the amount your MAGI exceeds the threshold — the lesser-of formula limits the tax for taxpayers just over the line |
| IRA distributions count as NII | Distributions from qualified retirement accounts (IRAs, 401(k)s) are excluded from NII; they raise MAGI but do not directly generate NIIT |
| The NIIT thresholds adjust for inflation each year like the standard deduction | The $200,000/$250,000 thresholds are fixed by statute and have not changed since 2013; no annual inflation adjustment applies |
| Municipal bond interest is subject to the NIIT | Tax-exempt interest from qualifying municipal bonds is explicitly excluded from NII |
| The NIIT and the Additional Medicare Tax are the same tax | They are two separate ACA surtaxes — the NIIT (3.8%) applies to investment income, while the Additional Medicare Tax (0.9%) applies to wages and self-employment income, each on its own IRS form |
| Real estate rental income is always subject to NIIT | Rental income from a real estate professional who materially participates is active, not passive, and is therefore excluded from NII |
Common Mistakes When Dealing with the NIIT
Ignoring MAGI effects of IRA distributions. The most common planning error is treating a large IRA withdrawal as NIIT-irrelevant simply because distributions are not NII. A $100,000 traditional IRA distribution that lifts MAGI from $220,000 to $320,000 converts $70,000 of investment income from below-threshold to above-threshold, generating $2,660 in NIIT on income that would otherwise have been exempt. Failing to model this interaction produces unpleasant tax surprises at filing.
Assuming the lesser-of formula means the NIIT is capped at a small amount. The lesser-of formula caps the NIIT at the amount corresponding to excess MAGI when excess MAGI is less than NII. But if your MAGI is substantially above the threshold, the excess-MAGI figure quickly becomes larger than NII, and the full NII amount is taxed. A single filer with $400,000 MAGI and $80,000 NII owes 3.8% on the full $80,000 ($3,040) because $200,000 of excess MAGI exceeds the NII.
Underestimating estimated-tax exposure. The NIIT is subject to estimated-tax requirements. Investors who receive large capital gain distributions late in the year — common with mutual funds and ETFs, which typically distribute in November and December — may find themselves owing NIIT they did not anticipate and did not make estimated payments for, triggering an underpayment penalty on top of the tax itself.
Year-End NIIT Checklist
- Estimate full-year MAGI and compare to threshold for your filing status.
- Calculate year-to-date net investment income (gains minus losses, plus dividends, interest, rents).
- Identify unrealized losses that can be harvested before December 31 without triggering wash-sale rules.
- Check whether any mutual fund or ETF positions are expected to distribute capital gains in November or December and model the NIIT impact.
- Verify that any IRA distributions, Roth conversions, or Social Security income have been included in the MAGI estimate.
- If MAGI is near the threshold, evaluate whether timing any income or deduction into a different year would save more in NIIT than it costs in other ways.
- Make any required estimated-tax payments for projected NIIT before January 15 of the following year to avoid underpayment penalties.
- File Form 8960 with Form 1040 if your MAGI exceeds the threshold and you have any net investment income.
Frequently Asked Questions
What is the Net Investment Income Tax?
The Net Investment Income Tax (NIIT) is a 3.8% surtax imposed by IRC §1411 on the net investment income of individuals, estates, and trusts whose modified adjusted gross income (MAGI) exceeds certain thresholds. It was enacted as part of the Affordable Care Act in 2010 and took effect January 1, 2013. The tax applies to the lesser of (a) your net investment income for the year or (b) the amount by which your MAGI exceeds the applicable threshold — $200,000 for single filers, $250,000 for married filing jointly. That means a taxpayer does not owe NIIT on all investment income, only on the portion that corresponds to the income above the threshold.
Who has to pay the 3.8% NIIT?
The NIIT applies to U.S. citizens and resident aliens whose MAGI exceeds $200,000 for single filers, $250,000 for married filing jointly (MFJ), $125,000 for married filing separately (MFS), or $200,000 for heads of household. Estates and trusts are subject to the NIIT on undistributed net investment income above the top income-tax-bracket threshold for estates and trusts, which is far lower than the individual thresholds. Nonresident aliens are not subject to the NIIT.
What income counts as net investment income for NIIT purposes?
Net investment income includes taxable interest, dividends (both qualified and ordinary), annuity income, capital gains from investments (both short-term and long-term), rental income net of deductions unless you qualify as a real estate professional who materially participates, royalties, passive activity income from businesses in which you do not materially participate, and gains from the sale of passive-activity property. Gains on the sale of a primary residence above the available exclusion ($250,000 single / $500,000 MFJ) also count.
What is excluded from the Net Investment Income Tax?
Wages and salaries, self-employment income, active business income from businesses you materially participate in, Social Security and pension income, alimony under pre-2019 agreements, distributions from tax-qualified retirement accounts (IRAs, 401(k)s, 403(b)s, pension plans), unemployment compensation, and tax-exempt interest from municipal bonds are all excluded from NII. An important nuance: IRA and 401(k) distributions are excluded from NII itself but they do increase your MAGI, which can push more of your other investment income over the threshold.
How does the NIIT interact with capital gains tax rates?
The NIIT stacks directly on top of regular capital gains rates. For 2026, the top long-term capital gains rate is 20% for the highest-income filers. Add the 3.8% NIIT and the effective top federal rate on long-term capital gains becomes 23.8%. Short-term capital gains are taxed as ordinary income — up to 37% at the top bracket — and the NIIT adds another 3.8% on top, for a potential combined federal rate of 40.8% on short-term gains above the NIIT threshold. State income taxes are on top of these federal rates.
Are the NIIT income thresholds adjusted for inflation?
No. The NIIT thresholds are not indexed for inflation. The $200,000 (single) and $250,000 (married filing jointly) thresholds have been fixed since the NIIT first took effect in 2013. That means more taxpayers cross the threshold each year through ordinary income growth, even without any real-terms increase in purchasing power. The same thresholds apply for 2026 as for 2013.
What is Form 8960 and how do I use it?
Form 8960, Net Investment Income Tax — Individuals, Estates, and Trusts, is the IRS form used to calculate and report the NIIT. Part I identifies gross investment income items such as interest, dividends, and gains. Part II subtracts allocable deductions to arrive at net investment income. Part III applies the 3.8% rate to the lesser of your NII or your excess MAGI, and that computed tax flows to your Form 1040. You attach Form 8960 to your regular federal income tax return if your MAGI exceeds the applicable threshold.
What are the most effective strategies for reducing NIIT exposure?
Effective NIIT reduction strategies include tax-loss harvesting to offset capital gains and reduce NII, timing large gain recognition to years when MAGI is below the threshold, making Roth IRA conversions in lower-income years to reduce future RMDs that raise MAGI, investing in qualified opportunity zone funds to defer and potentially reduce capital gains, using installment sales to spread gain recognition across multiple years, investing in tax-exempt municipal bonds whose interest is excluded from NII, maximizing contributions to tax-deferred retirement accounts to reduce MAGI, and for real estate investors, qualifying as a real estate professional to reclassify rental income as non-passive. Consult a qualified tax professional before implementing these strategies.
Sources and Methodology
This guide describes the Net Investment Income Tax as enacted in IRC §1411 and interpreted through Treasury Regulation §1.1411 and IRS guidance current through August 2026. Key sources include:
- Internal Revenue Code §1411: The governing statute, as enacted by the Health Care and Education Reconciliation Act of 2010 (Pub. L. 111-152), defines NII, the applicable thresholds, and the lesser-of formula.
- Treasury Regulation §1.1411: The final IRS regulations (T.D. 9644, 2013) provide detailed definitions of NII categories, allocable deductions, and the treatment of passive activity income, and are the basis for the NII categorization in this guide.
- IRS Form 8960 and Instructions: The 2025 form and instructions (current as of August 2026) document the line-by-line calculation described in the Form 8960 section.
- IRS Publication 550, Investment Income and Expenses: Documents the general treatment of interest, dividends, capital gains, and related deductions referenced throughout this guide.
- 2026 NIIT threshold confirmation: Web search conducted August 2026 confirmed that the $200,000/$250,000 thresholds remain unchanged and are not indexed for inflation, consistent with IRC §1411(b)(3).
This content was reviewed by the Swoopr Editorial Team in August 2026 and reflects publicly available information at that time. Tax laws are subject to change; verify current rates, thresholds, and form requirements with the IRS or a qualified tax professional before relying on any specific figure in this guide.
Conclusion
The Net Investment Income Tax is a 3.8% surtax that operates in parallel with ordinary income and capital gains tax rather than replacing them — which is why it's easy to underestimate or overlook. Its mechanics are defined by two things: what counts as NII (capital gains, dividends, interest, rents, and passive income — not wages or retirement distributions) and what the lesser-of formula means for investors near the threshold (the tax is limited by excess MAGI, not total NII, for those just over the line). Its thresholds have not moved in over a decade, which means the population of taxpayers it touches keeps growing. Understanding the formula, tracking MAGI proactively, and applying the right planning strategies — loss harvesting, installment sales, Roth conversions, muni bonds — is what separates investors who manage their NIIT exposure from those who simply pay whatever Form 8960 computes at filing.
Related Reading
- Stock & Investment Taxes — the parent hub for this content group, covering capital gains, wash sales, tax-loss harvesting, and other stock-investor tax topics.
- Short-Term vs. Long-Term Capital Gains — the holding-period rules that determine whether a gain is taxed at ordinary rates or preferential rates, and how each interacts with the NIIT.