Why It Matters
You pay NIIT when your MAGI exceeds $200,000 (single), $250,000 (married filing jointly), or $125,000 (married filing separately) — and you have investment income like rental profits, dividends, or capital gains. The surtax is 3.8% on the lesser of your net investment income or the amount your MAGI exceeds the threshold. Real estate professionals who materially participate in their rentals can exclude that income from the NIIT base entirely — one of the strongest financial arguments for pursuing RE Pro status.
At a Glance
- What it is: A 3.8% federal surtax on net investment income for taxpayers above the MAGI threshold
- Threshold: $200,000 (single/HOH), $250,000 (married filing jointly), $125,000 (married filing separately)
- What triggers it: Net rental income, dividends, interest, capital gains, passive business income
- What avoids it: W-2 wages, active business income, qualified retirement distributions, RE Pro rental income
- Key leverage: Real estate professional status removes rental income from the NIIT calculation
- Created by: Affordable Care Act, effective January 1, 2013; thresholds are NOT inflation-adjusted
NIIT = 3.8% × lesser of (Net Investment Income OR MAGI − Threshold)
How It Works
The surtax formula. NIIT equals 3.8% multiplied by the lesser of two figures: your net investment income for the year, or the amount by which your MAGI exceeds the threshold. If your excess MAGI is $30,000 but investment income is $45,000, NIIT applies only to $30,000 — the "lesser of" language caps the exposure.
What counts as net investment income. The IRS includes rental income (after deducting allowable expenses), dividends, taxable interest, capital gains, annuity income, and passive business income. "Net" means deductible expenses — mortgage interest, depreciation, property taxes, repairs — are subtracted before applying the 3.8%.
What is excluded. Wages, self-employment income, and active business income are not net investment income. Qualified retirement plan distributions are also excluded — even if they push your MAGI above the threshold.
The real estate professional exemption. Rental activities are passive by default, putting rental income squarely in NIIT territory. But when a taxpayer qualifies under the real estate professional test (750+ hours, majority of working time in real estate), rental income is reclassified as non-passive and excluded from the NIIT base. This is one of the highest-leverage intersections between RE Pro status and passive activity loss rules — for investors with significant rental income, it can eliminate the surtax entirely.
Real-World Example
Jennifer and her spouse file jointly. She earns $230,000 in W-2 income; combined MAGI is $272,000 after adding $42,000 in net rental income. The MFJ threshold is $250,000.
MAGI exceeds the threshold by $22,000; net investment income is $42,000. NIIT applies to the lesser: $22,000.
NIIT owed: $22,000 × 3.8% = $836.
Now consider what changes if Jennifer logs 803 hours this year and qualifies as a real estate professional, her rentals reclassified as non-passive. The $42,000 exits the net investment income bucket entirely. MAGI stays at $272,000, but with zero qualifying investment income, NIIT drops to $0 — a direct $836 saving with no deductions or offsets required. For investors with higher rental income, the exemption scales proportionally.
Pros & Cons
- Applies only to the "lesser of" figure, so exposure is capped when MAGI barely crosses the threshold
- Rental deductions — depreciation, mortgage interest, operating expenses — reduce net investment income before the 3.8% applies
- RE Pro status provides a clean exclusion: once you qualify, rental income leaves the NIIT base entirely
- Fixed thresholds create planning opportunities; investors near the cutoff can often use retirement contributions to stay below it
- The $250,000 MFJ threshold has not changed since 2013 — inflation has pulled more households in without any legislative adjustment
- RE Pro status requires strict hour documentation; investors who come close but fall short owe NIIT on all rental income
- Capital gains from property sales are net investment income — a profitable disposition can trigger NIIT even in a low-rental-income year
- Stacks on top of ordinary income and capital gains tax; investors in the 37% bracket face a 40.8% effective rate on rental income
Watch Out
- Threshold is MAGI, not taxable income. The standard deduction does not reduce MAGI. Retirement contributions to a traditional 401(k) or SEP-IRA do — verify this with your CPA before year-end if you are close to the threshold.
- Short-term capital gains count. Gains from flipping properties held less than one year are included in net investment income, not active business income (unless you are a licensed dealer). NIIT stacks on top of the ordinary income rate.
- RE Pro hours are per-spouse. Only one spouse's hours count toward the 750-hour requirement on a joint return. The other spouse's involvement does not combine toward RE Pro qualification.
- Primary residence gains above the exclusion. The $250,000/$500,000 gain exclusion eliminates NIIT on that portion — but any gain above the cap is net investment income subject to the full 3.8%.
Ask an Investor
The Takeaway
NIIT is a 3.8% surtax that catches high-income investors off guard — it activates at a fixed threshold that has never been adjusted for inflation, pulling more households in every year. If your MAGI exceeds $200,000 (single) or $250,000 (MFJ) and you have rental income or capital gains, you owe it on the smaller of your two exposures. RE Pro status is the most direct path to eliminating it on rental income — and combined with passive activity loss rules, it is one of the strongest tax arguments for investors building a serious portfolio.