Net Investment Income Tax (3.8% Surtax)

The net investment income tax (NIIT), also called the 3.8% surtax, is an additional federal tax on investment income triggered when your modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly). It applies to capital gains, dividends, interest, and rental income—adding a flat 3.8% on top of ordinary income tax and dramatically raising the true cost of selling appreciated assets or collecting passive income.

The 3.8% surtax: what it is and when it applies

The Net Investment Income Tax is a 3.8% surtax enacted in 2013 as part of the Affordable Care Act. It is not part of your ordinary income tax; it is a separate levy that applies only if your modified adjusted gross income (MAGI) exceeds $200,000 (single filers) or $250,000 (married couples filing jointly).

The tax applies to the lesser of:

1. Your net investment income, or
2. The amount by which your MAGI exceeds the threshold.

Example: A single filer with $250,000 MAGI and $80,000 in net investment income pays 3.8% tax on $50,000 (the excess over $200,000 threshold). Tax owed: $1,900. If the same filer had $30,000 in net investment income, the tax would be 3.8% × $30,000 = $1,140 (net investment income is the limiting factor).

What counts as “net investment income”

Net investment income includes:

• Long-term and short-term capital gains from the sale of stocks, bonds, real estate, or other assets.
• Qualified and non-qualified dividends from stocks and mutual funds.
• Interest income from bonds, savings accounts, and CDs.
• Rental and royalty income from leasing property or licensed intellectual property.
• Passive business income from a business in which you do not materially participate (e.g., a silent partnership).
• Commodities and derivatives gains (futures, options, swaps).

Net investment income excludes:

• W-2 wages and salary (active earned income).
• Business income from active businesses you materially participate in (self-employment income from your practice, shop, or consulting).
• Social Security benefits.
• Tax-exempt interest (municipal bonds).
• Insurance proceeds and certain death benefits.
• Qualified 401(k) and IRA distributions (the distribution itself is not subject to NIIT, though it counts toward MAGI, which can trigger the tax on your investment income).

The distinction between active and passive income is crucial. A real estate developer who actively participates in their business avoids NIIT on business profits, but a silent investor in the same deal pays 3.8% tax if thresholds are exceeded.

The cumulative hit: NIIT stacked on top of capital gains tax

A long-term capital gain is taxed twice if MAGI thresholds are exceeded. First, it is taxed at the long-term capital gains rate (0%, 15%, or 20% federally). Second, the 3.8% NIIT applies on top.

Example: A married couple with $300,000 MAGI (including $100,000 in long-term capital gains) in the 15% capital gains bracket pays:

• Capital gains tax: $100,000 × 15% = $15,000.
• NIIT: Lesser of (a) $100,000 net investment income or (b) $50,000 excess over $250,000 threshold = $50,000 × 3.8% = $1,900.
• Total federal tax on the gain: $16,900, or 16.9%.

In a high-tax state like California (13.3% on capital gains), the combined rate reaches 30.2%. The nominal “15% federal rate” obscures the true tax burden.

Modified AGI (MAGI) for NIIT purposes

Your MAGI for NIIT is not exactly the same as your standard tax return AGI. For NIIT, the IRS adds back certain deductions:

• Foreign earned income exclusion.
• Foreign housing exclusion or deduction.
• Exclusion for Puerto Rico bona fide residents.
• Excluded interest on savings bonds used for education.

For most investors, MAGI ≈ AGI. But those with foreign income or complex situations must verify their MAGI calculation.

The threshold—static, not indexed

Unlike tax brackets, the NIIT thresholds are not adjusted annually for inflation. They remain fixed at $200,000 (single) and $250,000 (married) indefinitely (unless Congress changes them). This means that as ordinary income grows with inflation or raises, more middle-class earners cross the threshold over time, expanding the NIIT tax base.

A couple with $250,000 income in 2013 (when NIIT started) was relatively uncommon; by 2024, such incomes are routine for dual-career households and small-business owners. Many middle-class professionals now pay NIIT without realizing it.

NIIT on rental property sales

A major trap: selling a rental property triggers NIIT on the long-term capital gain if MAGI exceeds the threshold. A couple selling a rental home for a $150,000 gain, with total MAGI of $280,000 (salary $130,000 + gain $150,000), owes:

• Long-term capital gains tax: $150,000 × 15% (approx.) = $22,500.
• NIIT: 3.8% × $30,000 (excess over $250,000) = $1,140.
• Total federal tax: $23,640, or 15.76% on the gain alone.

Many investors expect only the 15% rate and are shocked by the NIIT surprise.

NIIT applies despite 0% capital gains bracket

A taxpayer in the 0% long-term capital gains bracket still pays NIIT if MAGI exceeds the threshold. The 0% rate applies only to the income tax on gains; the 3.8% surtax is independent.

Example: A single filer with $150,000 AGI ($35,000 wages + $115,000 capital gains) has taxable income of $135,400 (after $14,600 standard deduction). The gain is taxed at 0% for income tax purposes. But MAGI of $150,000 exceeds the $200,000 threshold… wait, it does not. However, if AGI were $210,000 (via a $75,000 capital gain + $135,000 wages), the $10,000 excess triggers NIIT: 3.8% × $10,000 = $380.

The key: MAGI, not taxable income, triggers NIIT. A large gain raises MAGI even if the gain itself is taxed at 0%.

Planning strategies to avoid or defer NIIT

Defer realization: Do not sell appreciated assets if possible. Hold for estate/step-up in basis, donate to charity, or use 1031 exchanges to defer gains.

Time large gains: Realize gains in years when MAGI is lowest (sabbaticals, early retirement, low-income years). A couple timing a $200,000 asset sale into a year when they have no other income avoids NIIT entirely.

Direct charitable donations of appreciated assets: Donating appreciated securities directly to a charity avoids the capital gains tax and NIIT, while generating a charitable deduction. The donor gets a tax benefit, and the charity gets the full fair-market value without the investor triggering a $200,000+ MAGI from the gain.

Qualified small business stock (QSBS): Under IRC Section 1202, taxpayers may exclude 50–100% of long-term gains on certain small business stock held for five years, effectively dodging both capital gains tax and NIIT. Rare, but valuable for startup founders.

Shift income to lower-MAGI years: Move consulting work, freelance projects, or discretionary income recognition into years when you don’t have large gains.

State NIIT or equivalents

Most states do not have a direct counterpart to the federal NIIT. However, high-tax states like California apply high ordinary income or capital gains tax rates (13.3% on gains in California) that compound with the federal 3.8% NIIT, creating an effective rate above 40% in extreme cases (15% federal capital gains + 3.8% NIIT + 13.3% state).

A few states have their own high-earner surtaxes or net investment income taxes modeled on the federal version, but these are rare.

Checking NIIT on your return

The NIIT is reported on IRS Form 8960, “Net Investment Income Tax—Individuals, Estates, and Trusts.” Most tax software calculates it automatically if you have sufficient net investment income and MAGI exceeds the threshold. Investors with complex situations (passive business income, multiple investment accounts, real estate) should verify the calculation or hire a tax professional.

See also