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Net Investment Income Tax Calculator

A Roth conversion can increase NIIT without being investment income itself. Compare the 3.8% layer before and after an income change.

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Compare an income scenario

Illustrative starting values are prefilled. Replace them with your own inputs.

Use negative changes to test a reduction. A taxable IRA conversion belongs in the MAGI-only field. Enter only gains already included in taxable investment income.

Your calculation

NIIT before scenario
$0.00
NIIT after scenario
$1,140.00
Change in NIIT
$1,140.00
Filing-status threshold
$200,000
Scenario MAGI
$230,000
Scenario net investment income
$30,000
Scenario amount subject to NIIT
$30,000

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Educational estimate, updated September 29, 2026. Educational, not individualized tax advice. Individual taxpayer, entered NII is already classified and net of allocable deductions. Ordinary-income change affects MAGI only; investment-income change affects both MAGI and NII dollar for dollar. Only NIIT is calculated. Regular federal and state income taxes and other phaseouts are excluded.

Worked example

A $40,000 Roth conversion that pulls $30,000 of investment income into NIIT

A single filer with $190,000 of MAGI, including $30,000 of net investment income, converts $40,000 of a traditional IRA to Roth. The conversion is not investment income, but it raises MAGI above the $200,000 threshold.

Inputs

Worked example inputs
Filing statusSingle
Starting MAGI$190,000
Starting net investment income$30,000
Ordinary-income change (Roth conversion)$40,000
Investment-income change$0

Calculator output

Worked example calculator output
NIIT before the conversion$0.00
NIIT after the conversion$1,140.00
Change in NIIT$1,140.00
Scenario MAGI$230,000
Amount subject to NIIT$30,000

MAGI rises to $230,000, so the excess over $200,000 is $30,000. The lesser of that excess and the $30,000 of investment income is taxed at 3.8%. The conversion itself is still taxed as ordinary income, which this calculator does not show.

Methodology

How this calculator works

The calculator applies the individual net investment income tax to a before and after scenario and reports the difference.

Formulas

  • NIIT = 3.8% x the lesser of net investment income or MAGI minus the filing-status threshold (never below zero).
  • Thresholds: $200,000 single and head of household, $250,000 married filing jointly, $125,000 married filing separately.
  • An ordinary-income change moves MAGI only; an investment-income change moves both MAGI and net investment income.

Assumptions

  • You enter net investment income already classified and net of allocable deductions (Form 8960, Part I and II).
  • MAGI is adjusted gross income plus any foreign earned income exclusion, as defined for NIIT.
  • The thresholds are set by statute and are not adjusted for inflation, so they are the same in 2026.

What it ignores

  • Regular income tax and state tax on the same income.
  • Trust and estate NIIT, which uses a different threshold.
  • Investment income exclusions that need a facts review, such as active trade or business income and some real estate professional rental income.

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last reviewed October 20, 2026. Taxstra is a CPA firm serving 1,000+ clients in all 50 states.

Educational, not individualized tax advice.

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last updated October 20, 2026.

Separate investment income from the income threshold

For individuals, NIIT is 3.8% of the smaller of net investment income or MAGI above the filing-status threshold. It is an additional federal tax layer. This tool calculates that layer, then compares a scenario in which the entered income changes affect MAGI dollar for dollar.

  1. STEP 01

    Determine net investment income first

    Common included items are taxable interest, dividends, and taxable investment gains, reduced by properly allocable deductions. Wages, self-employment income, and qualified retirement-plan distributions generally are outside NII. Rental and business income needs careful classification; material participation and special real-estate rules cannot be inferred from a dollar amount.

  2. STEP 02

    Enter NIIT modified adjusted gross income

    MAGI for this tax generally starts with adjusted gross income and includes applicable foreign earned income adjustments. It is not taxable income after the standard or itemized deduction. The supported thresholds are $200,000 for single/head of household, $250,000 joint, and $125,000 married filing separately; they are not indexed annually.

  3. STEP 03

    Compare a clearly defined change

    Enter an ordinary-income change that affects MAGI but not NII, and an investment-income change included in both. This is a simplified sensitivity model: it does not determine whether an expense, loss, sale, or Roth conversion changes MAGI and NII by the same amount in your return. It also excludes ordinary income tax, state taxes, and other phaseouts.

Worked threshold examples

Single-filer illustrations; all investment amounts are already properly classified net investment income.

Swipe horizontally to compare

ScenarioMAGINIINIIT baseNIIT
Starting return$190,000$30,000$0$0
Add $40,000 ordinary income$230,000$30,000$30,000$1,140
NII smaller than excess MAGI$300,000$10,000$10,000$380

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Frequently asked questions

Does a Roth conversion count as investment income?

A taxable IRA conversion generally increases MAGI but is not itself NII. It can expose existing investment income to NIIT by moving MAGI above the threshold. The calculator separates those two inputs.

Is NIIT charged on all income above the threshold?

No. The base is limited to net investment income. A taxpayer with high wages but no NII does not owe this tax solely because wages exceed the threshold.

Does rental income count?

It can, but passive status, trade-or-business treatment, and real-estate-specific rules can change the answer. Enter only NII already classified for Form 8960; this tool does not determine whether a rental qualifies for an exclusion.

Do qualified dividends count?

Generally yes. Preferential regular income-tax treatment does not automatically remove dividends from NIIT. Use net investment income after the applicable Form 8960 adjustments.

Can I use a negative scenario change?

Yes, if the resulting MAGI and NII stay nonnegative and the specified change actually affects each base as stated. This shows sensitivity, not a recommendation to realize a loss or alter a conversion.

Does this calculate the total tax on a sale?

No. Capital-gains tax, depreciation recapture, ordinary income tax, and state tax are separate. Use this result as the NIIT layer after the sale’s taxable income has been classified.

Related services and resources

Capital gains tax guide

Understand the regular federal tax before adding NIIT.

Explore

Rental property and NIIT

Read the rental classification discussion.

Explore

Roth conversion calculator

Explore the separate regular income-tax effects.

Explore

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