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.
Book a free consultationCompare 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.
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.
- 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.
- 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.
- 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
| Scenario | MAGI | NII | NIIT base | NIIT |
|---|---|---|---|---|
| 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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Authoritative Sources
Citations reflect U.S. federal tax law as of the article's last reviewed date.
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.
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