The Net Investment Income Tax (NIIT) — the 3.8% surtax created by the Affordable Care Act — has been in effect since 2013, yet it still catches taxpayers by surprise. Unlike most taxes that are triggered by crossing a threshold, the NIIT sits on top of your regular income tax and capital gains tax, effectively raising the top long-term capital gains rate from 20% to 23.8%, the top short-term/ordinary rate from 37% to 40.8%, and the tax on rental and passive income by an additional 3.8 percentage points.
Understanding what triggers the NIIT — and what you can do about it — is essential for investors, retirees with significant investment income, and anyone approaching the income thresholds.
How the NIIT Works
The NIIT is 3.8% of the lesser of:
- Your net investment income for the year, or
- The amount by which your modified adjusted gross income (MAGI) exceeds the threshold:
- $200,000 for single filers and head of household
- $250,000 for married filing jointly
- $125,000 for married filing separately
The tax is calculated on Form 8960 and reported on your Form 1040.
What Counts as Net Investment Income
Net investment income includes three categories, reduced by deductions properly allocable to each:
Category 1 — Interest, dividends, annuities, royalties, and rents:
- Taxable interest (bank accounts, bonds, CDs)
- Tax-exempt interest is not included (municipal bond interest does not trigger NIIT)
- Ordinary dividends and qualified dividends (both count)
- Short-term capital gains (taxed at ordinary rates plus the 3.8% NIIT on top)
- Long-term capital gains (taxed at 0%/15%/20% plus the 3.8% NIIT on top — effectively making the top federal rate 23.8%)
- Rental income from property where the activity is passive or the property is triple-net-leased
- Royalty income
- Annuity income (the taxable portion)
Category 2 — Passive activity income:
- Income from a trade or business in which you do not materially participate
- Income from rental real estate where you are not a real estate professional
- Income from limited partnerships and certain LLCs where you are a passive investor
Category 3 — Gains from the disposition of property:
- Capital gains from selling stocks, bonds, mutual funds, ETFs, crypto, second homes, investment real estate
- Gains from selling a business or business assets (the portion attributable to investment, not active business)
- Gain from selling your primary residence above the exclusion amount ($250,000 single / $500,000 MFJ) is included
What Does NOT Count as Net Investment Income
- Wages, salaries, bonuses (subject to FICA and Medicare surtax separately, but not NIIT)
- Self-employment income from a trade or business in which you materially participate
- Social Security benefits
- Tax-exempt municipal bond interest
- Distributions from qualified retirement plans (401(k), Traditional IRA, 403(b)) — but note: those distributions increase your MAGI, which can push you over the threshold and cause your other investment income to become subject to NIIT
- Roth IRA distributions (qualified) — both excluded from NII and from MAGI
- Alimony received (for pre-2019 divorce agreements)
- Unemployment compensation
Thresholds and MAGI Calculation
Your MAGI for NIIT purposes is your adjusted gross income (AGI) with certain modifications — but for most taxpayers, AGI and NIIT MAGI are the same or very close. The primary difference is that foreign earned income excluded under the Foreign Earned Income Exclusion (Form 2555) is added back to AGI for NIIT purposes, so expats with excluded foreign income may owe NIIT even with a low US AGI.
Threshold examples:
| Filing Status | MAGI Threshold | Scenario | NIIT Applies? |
|---|---|---|---|
| Single | $200,000 | $180,000 MAGI, $50,000 NII | No — below threshold |
| Single | $200,000 | $220,000 MAGI, $50,000 NII | Yes — 3.8% × $20,000 = $760 |
| Single | $200,000 | $220,000 MAGI, $10,000 NII | Yes — 3.8% × $10,000 = $380 |
| MFJ | $250,000 | $300,000 MAGI, $80,000 NII | Yes — 3.8% × $50,000 = $1,900 |
| MFJ | $250,000 | $240,000 MAGI, $100,000 NII | No — below threshold |
In the third example, the NIIT is on $10,000 (the NII) rather than $20,000 (the excess MAGI) because the NIIT applies to the lesser of NII and excess MAGI. If most of your income is from wages, only the investment income portion above the threshold is subject to the surtax.
What You Can Do About It
There is no single “NIIT loophole.” The surtax is broadly drafted and applies across investment income categories. But there are strategies — all legitimate — that reduce its impact.
1. Manage Your MAGI (Especially Near Thresholds)
If your MAGI is near the threshold, relatively small moves can make the difference:
- Maximise pre-tax retirement contributions: 401(k) contributions ($23,500 in 2026, plus $11,250 catch-up for 60–63), Traditional IRA contributions (deductible if eligible), HSA contributions ($4,300 single / $8,550 family in 2026). All of these reduce MAGI.
- Defer income to a later year: If you are near the threshold and can time the sale of an appreciated asset (or the receipt of a bonus payable in a future year), shifting income can keep you below the NIIT threshold. This is especially relevant for retirees managing RMD timing.
- Harvest tax losses: Realising capital losses reduces capital gains and therefore MAGI. Even if you have no gains to offset, up to $3,000 in net capital losses can offset ordinary income and reduce MAGI.
2. Shift Investments to Tax-Exempt or Tax-Deferred Vehicles
- Municipal bonds: Interest is excluded from NII and from MAGI. For high-income investors in high-tax states, muni bonds in taxable accounts are a direct NIIT-avoidance tool.
- Max out retirement accounts: Investments inside a 401(k) or IRA grow without generating annual NII (no NIIT on undistributed gains or dividends within the account). Distributions are still not NII, though they increase MAGI.
- Roth IRA: Qualified distributions are excluded from both NII and MAGI. A Roth conversion ladder (converting Traditional IRA assets to Roth in lower-income years, below the NIIT threshold) can reduce long-term NIIT exposure.
- Health Savings Account (HSA): Contributions reduce MAGI. Investment growth inside the HSA is not NII. Qualified distributions are tax-free. The HSA is effectively triple-protected against NIIT.
- 529 plans: Growth and qualified distributions are not NII.
3. Structure Rental Real Estate to Avoid Passive Classification
If you materially participate in rental real estate — and can meet the real estate professional rules (750+ hours, more than half your working time in real property trades or businesses) — the rental income is reclassified from passive to non-passive, removing it from the NII base.
Even without full real estate professional status, grouping rental properties into a single activity and meeting the material participation standard for that grouped activity may reclassify the income. This is a facts-and-circumstances determination and requires careful documentation of hours.
Important caveat: The IRS scrutinizes real estate professional claims. The hours log needs to be contemporaneous and credible. A full-time software engineer claiming 750 hours of real estate activity while working a W-2 job is likely to face an audit challenge.
4. Time Capital Gains
The NIIT makes the difference between realising a gain in one year vs spreading across multiple years more valuable. For a married couple with $200,000 in other income:
- Realising a $100,000 long-term gain in a single year: $50,000 above the $250,000 MFJ threshold × 3.8% = $1,900 in NIIT
- Splitting the sale across two tax years ($50,000 each): both years stay below $250,000 MAGI = $0 NIIT (assuming income is consistent)
The 3.8% surtax is smaller than the federal capital gains rate (15% or 20%), so NIIT should not dominate the decision — but it does increase the after-tax cost of bunching gains into a single year.
5. Qualified Dividends, Long-Term Gains, and Bracket Management
Since qualified dividends and long-term capital gains are included in both MAGI and NII, a large long-term capital gain can push your MAGI above the NIIT threshold even if your “ordinary” income is below it. A single filer with $150,000 in wages and $80,000 in long-term capital gains has a MAGI of $230,000 — $30,000 above the threshold. The NIIT applies to $30,000 × 3.8% = $1,140.
Managing the timing and size of long-term gains relative to your ordinary income base is the most effective NIIT planning lever for most investors.
NIIT and Estimated Tax Payments
The NIIT is part of your total tax liability and must be covered by withholding or estimated tax payments. If you expect significant investment income — from a planned stock sale, a large mutual fund capital gains distribution in December, or rental income — factor the NIIT into your quarterly estimated payment calculations to avoid underpayment penalties.