Net Investment Income Tax Guide

What the Net Investment Income Tax Is

The Net Investment Income Tax is a 3.8% tax on investment income for higher-income taxpayers, created by the Affordable Care Act and effective for tax years beginning after December 31, 2012. It lives in IRC §1411, sits outside the regular income tax, and is computed on its own form, Form 8960. It applies to individuals, estates, and trusts, but not to corporations or to nonresident aliens.

The tax is not a flat 3.8% on all investment income. It is 3.8% of the smaller of two numbers: your net investment income, or the amount by which your modified adjusted gross income exceeds a fixed threshold. That lesser-of design is the single most important feature of the tax and the source of most of its surprises. A taxpayer with substantial dividends and gains can owe nothing in a year their MAGI stays under the threshold, then owe thousands in a year a single event lifts MAGI over the line.

Two design choices drive almost every practical problem. First, like the related Additional Medicare Tax, the thresholds are fixed by statute and never adjust for inflation, so wage and portfolio growth pull more taxpayers over the line each year. Second, the tax keys off MAGI, not off investment income alone, so income that is not itself subject to the NIIT - a large IRA withdrawal, a Roth conversion, a one-time bonus - can still trigger it by raising MAGI. The rest of this guide works through both.

The MAGI Thresholds (and Why They Never Change)

The threshold depends only on your filing status:

These amounts are written directly into §1411(b). Unlike tax brackets, the standard deduction, or retirement limits, there is no cost-of-living adjustment, so the figures have not moved since 2013 and will not move unless Congress amends the statute. Note that the qualifying surviving spouse threshold is the full $250,000 joint amount, which differs from the Additional Medicare Tax, where a surviving spouse uses the $200,000 figure.

MAGI for the NIIT is a narrow modification: it is your adjusted gross income (Form 1040, line 11) increased by any foreign earned income you excluded under §911, net of the deductions that exclusion disallowed. For taxpayers with no foreign earned income exclusion, which is most filers, MAGI for the NIIT simply equals AGI. That makes the AGI line the practical control point for the tax.

What Counts as Net Investment Income

Net investment income is built from three categories of gross income under §1411(c), then reduced by allocable deductions. The three categories are:

• Portfolio income: taxable interest, dividends (ordinary and qualified), annuities, royalties, and rents, except amounts earned in the ordinary course of a non-passive trade or business.
• Passive and trading income: income from a trade or business that is a passive activity under §469, and income from a business of trading in financial instruments or commodities.
• Net gain: net gain from the disposition of property, except property held in a non-passive trade or business. This includes capital gains on stocks, bonds, mutual funds, and investment real estate.

Qualified dividends and long-term capital gains keep their preferential income-tax rate under §1(h), but they are still fully net investment income for the 3.8%. That is why a high-income investor effectively pays 18.8% or 23.8% on long-term gains: the 15% or 20% capital-gains rate plus the 3.8% NIIT. The Qualified Dividends & Capital Gains Tax Calculator models the income-tax side of that stack, and this guide's calculator models the 3.8% on top.

Rental income is the most fact-sensitive category. For a typical landlord with a separate full-time job, rental income is passive and counts. A taxpayer who qualifies as a real estate professional under §469 and materially participates may treat the rental as non-passive and keep it out of the base. The Rental Income Tax Calculator covers the income-tax mechanics of rental activity.

The Lesser-Of Rule: How the Tax Is Calculated

The NIIT equals 3.8% of the smaller of two amounts:

• Your net investment income (Form 8960, line 12) - total investment income minus allocable expenses; or
• Your MAGI over the threshold (line 15) - MAGI minus your filing-status threshold, floored at zero.

Whichever is smaller becomes the base on line 16, and 3.8% of it is the tax on line 17. The rule produces three distinct outcomes:

• MAGI under the threshold. Line 15 is zero, so the tax is zero regardless of how much investment income you have. This is the relief valve.
• MAGI just over the threshold. The MAGI excess is small, so you pay only on that thin slice even if your investment income is large. A single filer with $200,000 of investment income but MAGI of $210,000 pays 3.8% of $10,000, which is $380.
• MAGI far over the threshold. The MAGI excess exceeds your investment income, so you pay 3.8% on your full net investment income. A single filer with $60,000 of investment income and MAGI of $400,000 pays 3.8% of $60,000, which is $2,280.

The practical lesson is that the NIIT is really a tax on the interaction between two numbers. Lowering either one - reducing realized investment income, or reducing MAGI through deductions, deferral, or income timing - reduces the tax. The calculator shows which of the two is binding so you know which lever to pull.

What Is Excluded from the NIIT

Several large income types are specifically outside net investment income, and confusing them for included income is the most common error:

• Wages and self-employment income. Earned income is never net investment income (§1411(c)(6)); it faces the separate 0.9% Additional Medicare Tax instead.
• Qualified plan and IRA distributions. Distributions from plans under §401(a), 403(a), 403(b), 408, 408A, and 457(b) are excluded by §1411(c)(5). A 401(k), traditional or Roth IRA, 403(b), or governmental 457(b) distribution is never NIIT income.
• Social Security benefits. The taxable portion of Social Security is ordinary income, not net investment income.
• Tax-exempt interest. Municipal bond interest excluded from income is also outside net investment income (and outside MAGI for this tax).
• Active business income. Income from a trade or business in which you materially participate, and that is not a trading business, is excluded.
• Excluded home-sale gain. Gain on a main home that you exclude under the §121 exclusion ($250,000 single, $500,000 joint) is not net investment income; only the taxable excess counts. The Home Sale Capital Gains Calculator works out that exclusion.

Allocable Investment Expenses

Net investment income is net of expenses properly allocable to that income. On Form 8960, Part II, the deductible expenses are:

• Investment interest expense (line 9a). Interest on debt allocable to property held for investment, the same amount allowed on Form 4952. Our Investment Interest Expense Calculator works through that limitation.
• State, local, and foreign income tax (line 9b). The portion of those income taxes allocable to your net investment income, subject to the overall SALT limit on Schedule A.
• Miscellaneous investment expenses (line 9c). Items such as investment advisory fees once went here, but they are suspended under IRC §67(g) and are not deductible. The 2025 One Big Beautiful Bill Act made that suspension permanent, so line 9c stays at zero going forward.

Because advisory fees and similar costs are no longer deductible, the realistic deductions for most investors are investment interest expense and allocable state income tax. The smaller your deductible expenses, the closer net investment income sits to gross investment income.

Form 8960 Walkthrough: Where It Goes on Your Return

You must file Form 8960 if you have any net investment income and your MAGI exceeds your threshold. The form has three parts:

• Part I - Investment Income (lines 1-8). Taxable interest (line 1), dividends (line 2), annuities (line 3), net rental, royalty, partnership, and S corporation income (line 4a, adjusted on 4b), net gain from disposition of property (line 5a, adjusted on 5b-5d), other modifications (line 7), and the total on line 8.
• Part II - Investment Expenses (lines 9-11). Investment interest expense (9a), state, local, and foreign income tax allocable to NII (9b), miscellaneous investment expenses (9c, currently suspended), and the total deductions on line 11.
• Part III - Tax Computation (lines 12-17). Net investment income (line 12 = line 8 minus line 11), MAGI (line 13), threshold (line 14), MAGI over threshold (line 15), the smaller of line 12 or 15 (line 16), and the NIIT at 3.8% (line 17).

Line 17 carries to Schedule 2 (Form 1040), line 12 and joins your total tax. There is no withholding line and no reconciliation: the entire tax is settled on the return. Estates and trusts use the same form but compare undistributed net investment income against AGI over the top trust bracket under §1(e), a far lower threshold (about $15,650 for 2025). The calculator labels its breakdown with these line numbers so you can trace each figure onto the form.

The 3.8% NIIT vs the 0.9% Additional Medicare Tax

The NIIT is one of two ACA-era surtaxes that share the same dollar thresholds, and they are constantly confused:

A high earner can owe both in one year, but never both on the same dollar: portfolio dollars face the 3.8%, salary dollars the 0.9%. An executive with a $400,000 salary and a $50,000 capital gain files both Form 8960 (on the gain) and Form 8959 (on the wages). The wage surtax is modeled in our Additional Medicare Tax Calculator; the Additional Medicare Tax Guide covers the earned-income side in full.

Planning Moves and Estimated Payments

Because the tax keys off the interaction of net investment income and MAGI, the levers are on both sides:

• Manage MAGI. Maximizing pre-tax retirement contributions, harvesting capital losses, and timing income can keep MAGI under the threshold in years you are close. Even partial relief helps because the tax is on the excess, not a cliff.
• Spread one-time events. A large Roth conversion, a property sale, or an inherited-account drawdown can be split across two tax years so neither year clears the threshold by much. Confirm the MAGI impact first with the AGI and MAGI Calculator.
• Use tax-exempt and tax-deferred vehicles. Municipal bond interest is outside both net investment income and MAGI; tax-deferred growth inside a retirement account is not NIIT income when it grows, only AGI when distributed.
• Cover it with estimates. Nothing is withheld for the NIIT. If you expect to owe it, build it into quarterly estimated payments or add extra income tax withholding on Form W-4, line 4c, so a correct-but-unpaid balance does not generate a §6654 penalty. The Quarterly Tax Calculator handles the safe-harbor math.

The 2025 One Big Beautiful Bill Act did not change §1411, so the 3.8% rate, the thresholds, and the definition of net investment income carry forward unchanged. For most taxpayers this remains a tax to anticipate around income events, not a tax to permanently avoid.

Practitioner Insight (LMN Tax Inc.)

Real-World Scenarios

When the General Rules Do Not Apply

• Estates and trusts. A trust or estate owes the NIIT on the lesser of undistributed net investment income or AGI over the top §1(e) trust bracket (about $15,650 for 2025), a much lower threshold than the individual amounts, which makes accumulating trusts highly exposed.
• Real estate professionals. A materially-participating real estate professional under §469 may treat rental income as non-passive and exclude it from net investment income; the determination is fact-specific and contested in audits.
• Sale of a passthrough interest. Gain on selling a partnership interest or S corporation stock is adjusted on Form 8960, line 5c to the portion attributable to the entity's net investment property, a basis computation outside a single-figure estimate.
• Section 1411 NOL and special modifications. Line 7 carries §1411 net operating losses, Form 8814 child-income elections, and CFC/PFIC adjustments that simple estimates miss.
• Nonresident aliens. A nonresident alien is not subject to the NIIT, with special rules for a dual-status year and for a §6013(g) or (h) election to treat a nonresident spouse as a resident.
• Installment sales. Gain reported under the installment method spreads the net gain across years, so the NIIT can apply in each year the installment is collected rather than all at once.
• State surtaxes. The 3.8% is federal. Most states have no parallel tax, but check your state return, as a few reach the same income through their own high brackets.

Frequently Asked Questions

What to Do Next