Net Investment Income Tax (NIIT): Definition and How the 3.8% Surtax Works

The Net Investment Income Tax (NIIT) is a 3.8% federal surtax imposed under IRC §1411 on the lesser of (1) a taxpayer's net investment income (NII) or (2) the amount by which the taxpayer's modified adjusted gross income (MAGI) exceeds a statutory threshold. The thresholds are $200,000 for single filers, $250,000 for married filing jointly, $125,000 for married filing separately, and $200,000 for qualifying surviving spouses. These thresholds have never been adjusted for inflation since the tax took effect in tax years beginning after December 31, 2012, under the Health Care and Education Reconciliation Act of 2010 (Pub. L. 111-152). The NIIT is reported on Form 8960 and flows to the taxpayer's Form 1040.

What Income Is Subject to NIIT

Net investment income under IRC §1411(c)(1) consists of three categories:

  1. Gross income from interest, dividends, annuities, royalties, and rents — unless derived from a trade or business that is not passive and is not a trade or business of trading in financial instruments or commodities
  2. Gross income derived from a trade or business that is a passive activity under IRC §469, or from a business of trading in financial instruments or commodities under IRC §475(e)(2)
  3. Net capital gains — from the disposition of property (other than property held in a trade or business that is not passive), reduced by any allowable capital loss deduction

Income categories that are not subject to NIIT include:

  • Wages, salaries, and self-employment income
  • Distributions from qualified retirement plans (401(k), IRA, pension)
  • Tax-exempt municipal bond interest
  • Active business income in which the taxpayer materially participates
  • Social Security benefits, unemployment compensation
  • Income from farming activities

How the NIIT Is Calculated

The tax equals 3.8% × the lesser of:

  • Total net investment income for the year, or
  • The excess of MAGI over the applicable filing-status threshold

Example: A married couple filing jointly has MAGI of $320,000 and net investment income of $60,000. The MAGI excess over $250,000 is $70,000. NIIT applies to the lesser figure — $60,000 — resulting in NIIT of $60,000 × 3.8% = $2,280.

If the same couple has MAGI of $320,000 but NII of $80,000, NIIT applies to the $70,000 MAGI excess: $70,000 × 3.8% = $2,660.

NIIT and Passive Activity Loss Rules

The intersection of NIIT with the passive activity rules under IRC §469 is particularly significant. Income from a passive activity — a business in which the taxpayer does not materially participate, or any rental activity — is generally included in NII. Conversely, losses from passive activities can offset passive income for NIIT purposes, but suspended passive activity losses that have not yet been released do not reduce NII in the year they are generated.

When a passive activity is disposed of in a fully taxable transaction, the released suspended losses reduce NII in that year, potentially eliminating NIIT on the disposition gain. Planning for the timing of passive activity dispositions is therefore a meaningful NIIT reduction strategy.

NIIT and Capital Gains Stacking

Long-term capital gains are included in NII and also increase MAGI, potentially pushing more income above the NIIT threshold. For higher-income taxpayers, the effective federal rate on long-term capital gains subject to NIIT is 23.8% (20% long-term capital gains rate + 3.8% NIIT). For taxpayers in the 15% capital gains bracket who are close to the MAGI threshold, a large capital gain can push MAGI above the threshold and expose part of the gain to NIIT.

See Capital Gains Tax Rates: Short-Term vs Long-Term for the interaction of NIIT with the tiered capital gains rate structure.

How CPAs and Tax Advisors Use This

For CPAs, the NIIT is a regular planning consideration for clients with investment portfolios, rental properties, or passive business interests. Key applications include:

  • Threshold monitoring: Tracking projected MAGI throughout the year to estimate whether the threshold will be crossed and by how much
  • Harvesting and deferral: Timing capital gain realizations to stay under the NIIT threshold, or harvesting capital losses to reduce NII
  • Material participation analysis: Helping clients with passive business interests establish material participation (via the seven tests under Treas. Reg. §1.469-5T) to reclassify income as non-passive and remove it from NII
  • Roth conversion sequencing: Roth conversions add to MAGI and can trigger or increase NIIT exposure; the conversion amount must be modeled against NII before executing
  • Entity-level planning: For S corporation shareholders and partnership interests, NIIT treatment depends on whether the owner materially participates

For a comprehensive guide to reducing NIIT exposure, see Net Investment Income Tax Planning Strategies for 2026.

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