Does this calculator implement all of the detailed NIIT rules?

No. It uses a simplified formula and thresholds to provide a quick estimate. Actual NIIT calculations can involve detailed classifications of income, adjustments, and interactions with other parts of the tax code. For precise results, use tax software or consult a tax professional.

Are the thresholds and 3.8% rate guaranteed to stay the same?

Tax laws can change. The thresholds and 3.8% rate in this calculator reflect current NIIT rules at the time of design. Always verify against current IRS guidance or professional advice, especially for future‑year planning.

Does this tool account for state or local taxes on investment income?

No. NIIT is a federal tax. States and localities may impose their own taxes on investment income, which are separate from the 3.8% NIIT and are not modeled here.

How should I enter capital gains and losses?

Enter your net investment income after considering capital gains and capital losses in aggregate. For example, if you have $40,000 in gains and $10,000 in losses, you might enter $30,000 as your net investment income for this simplified estimate.

Is the output from this calculator enough to file my taxes?

No. The output is an educational estimate only. Filing NIIT accurately requires following IRS instructions and potentially accounting for many details not captured here. Always rely on official IRS forms, tax software, and/or a qualified tax advisor for actual filing.

finance calculator

Net Investment Income Tax (NIIT) Calculator

Estimate NIIT (3.8%) based on net investment income, AGI, and filing status thresholds.

Results

NIIT threshold: $250,000
AGI above threshold: $0
NIIT base (lesser of NII or excess AGI): $0
Estimated NIIT (3.8%): $0

Overview

For higher‑income taxpayers in the U.S., investment income can be subject to an additional 3.8% Net Investment Income Tax (NIIT) on top of regular income or capital gains taxes. The NIIT applies only when your income exceeds certain thresholds and only to the lesser of your net investment income or the amount by which your adjusted gross income (AGI) exceeds the threshold. This calculator provides a simplified NIIT estimate so you can see whether the tax might apply and roughly how large it could be.

How to use this calculator

Estimate your net investment income for the year, combining interest, dividends, capital gains, and other passive investment income, net of allowable investment expenses in a simplified way.
Enter your adjusted gross income (AGI) from your tax planning software or a projection; this is your income after adjustments but before standard or itemized deductions.
Choose your filing status (Single, Head of Household, or Married Filing Jointly) so the calculator can apply the appropriate NIIT threshold.
Run the calculation to see the threshold amount, how much of your AGI is above that threshold, the NIIT base (lesser of NII and excess AGI), and the resulting estimated NIIT.
Experiment with different NII and AGI values—for example, before and after realizing capital gains or harvesting losses—to see how NIIT might change.

Inputs explained

Net investment income: A simplified total of your investment income subject to NIIT. This can include interest, dividends, annuities, rents and royalties (if not derived in the ordinary course of a trade or business), passive activity income, and net capital gains. In this calculator, you enter a single net figure after capital losses and related adjustments.
Adjusted gross income (AGI): Your AGI as used on your federal tax return, which includes wages, investment income, and other income items after allowable adjustments but before standard or itemized deductions. NIIT thresholds are based on AGI, not taxable income.
Filing status: Your federal filing status—Single, Head of Household, or Married Filing Jointly. Each status has a different NIIT threshold in this simplified model. Other filing statuses are not modeled here.

Outputs explained

NIIT threshold: The income threshold for NIIT based on your filing status (for example, $200,000 for Single or Head of Household and $250,000 for Married Filing Jointly in this simplified setup). Your NIIT exposure generally starts only when AGI exceeds this amount.
AGI above threshold: The amount by which your AGI exceeds the NIIT threshold. If this value is zero or negative, you are below the threshold and the simplified calculation produces a NIIT of $0.
NIIT base (lesser of NII or excess AGI): The amount of income subject to the 3.8% NIIT, defined as the lesser of your net investment income and your AGI above the threshold. This reflects the rule that you only pay NIIT on the smaller of these two amounts.
Estimated NIIT (3.8%): The estimated Net Investment Income Tax, computed as 3.8% of the NIIT base. This is an additional federal tax that sits on top of your regular income and capital gains taxes.

How it works

You enter your net investment income (NII), your adjusted gross income (AGI), and your filing status. Net investment income is a broad category that can include interest, dividends, capital gains, rental income (for non‑real estate professionals), and certain passive income streams.

The calculator uses simplified NIIT thresholds: for example, $200,000 for Single and Head of Household filers and $250,000 for Married Filing Jointly. These thresholds are not indexed for inflation and can differ by filing status.

We compute your excess AGI by subtracting the threshold for your filing status from your AGI. If AGI is at or below the threshold, excess AGI is zero and NIIT does not apply in this simplified model.

The NIIT base is the lesser of your net investment income and your excess AGI. This reflects the rule that the 3.8% tax applies only to the portion of NII that falls above the threshold, not to all of your investment income if AGI barely crosses the line.

Finally, we multiply the NIIT base by 3.8% (0.038) to produce an estimated Net Investment Income Tax amount.

This is a simplified calculation and does not model all subtleties of NIIT law, but it gives you a clear sense of whether NIIT is likely in play and at what approximate scale.

Formula

Threshold (T) = based on filing status (e.g., $200,000 for Single/HOH, $250,000 for MFJ in this simplified model)\nExcess AGI = max(0, AGI − T)\nNIIT base = min(Net investment income, Excess AGI)\nEstimated NIIT = NIIT base × 3.8% (0.038)

When to use it

Checking whether projected income for the year is likely to trigger NIIT and, if so, roughly how large the additional tax might be.
Evaluating the NIIT impact of realizing additional capital gains, such as selling appreciated stock or property.
Exploring how tax‑loss harvesting or deferring investment income could affect NIIT exposure by reducing net investment income or AGI.
Helping high‑income investors understand how NIIT interacts with their broader tax planning and why some income is taxed at more than just the normal capital gains or ordinary income rates.
Using NIIT estimates alongside capital gains and marginal tax calculators to model total tax on investment scenarios.

Tips & cautions

If your AGI is below the threshold for your filing status, NIIT is typically zero in this simplified framework—regardless of how much investment income you have.
If your AGI is only slightly above the threshold, NIIT may apply to only a portion of your net investment income, not the entire amount.
Consider both levers—net investment income and AGI—when planning: lowering either one can reduce NIIT exposure.
For large transactions (such as selling a business, rental property, or large stock position), projecting NIIT ahead of time can prevent surprise tax bills.
Remember that NIIT is federal; states may have their own taxes on investment income that are separate from the 3.8% NIIT.
This calculator uses simplified NIIT thresholds and does not adjust for all filing statuses, inflation, or potential future law changes.
It treats net investment income and AGI as single summary inputs and does not model detailed line‑item adjustments, exclusions, or special categories (for example, income from certain retirement accounts).
It does not account for interactions between NIIT and other parts of the tax code, such as phaseouts, alternative minimum tax, or specific rules for rental real estate professionals.
The 3.8% rate and thresholds are based on current NIIT rules at the time of design; tax laws may change, and historic years can have different nuances.
The output is an estimate for planning and education, not an official tax calculation suitable for filing or compliance.

Worked examples

$20,000 net investment income, $250,000 AGI, Married Filing Jointly

Threshold for MFJ (simplified) = $250,000.
Excess AGI = max(0, 250,000 − 250,000) = $0.
NIIT base = min($20,000, $0) = $0.
Estimated NIIT = $0 × 0.038 = $0 (no NIIT in this scenario).

$30,000 net investment income, $300,000 AGI, Married Filing Jointly

Threshold for MFJ = $250,000.
Excess AGI = max(0, 300,000 − 250,000) = $50,000.
NIIT base = min($30,000, $50,000) = $30,000.
Estimated NIIT = $30,000 × 0.038 = $1,140.

$50,000 net investment income, $210,000 AGI, Single filer

Threshold for Single = $200,000.
Excess AGI = max(0, 210,000 − 200,000) = $10,000.
NIIT base = min($50,000, $10,000) = $10,000.
Estimated NIIT = $10,000 × 0.038 = $380 (only a portion of NII is subject to NIIT).

Deep dive

This Net Investment Income Tax (NIIT) calculator estimates the 3.8% surtax that can apply to higher‑income taxpayers with investment income. By entering your net investment income, adjusted gross income (AGI), and filing status, you can see the NIIT threshold, how far above it your AGI sits, the portion of income subject to NIIT, and an estimated NIIT amount.

Use it as a planning tool alongside capital gains and marginal tax calculators to understand the full tax impact of investment decisions. While it simplifies complex rules into a clear formula, it helps highlight when NIIT may be in play and motivates deeper conversations with tax professionals before large transactions.

FAQs

Does this calculator implement all of the detailed NIIT rules?: No. It uses a simplified formula and thresholds to provide a quick estimate. Actual NIIT calculations can involve detailed classifications of income, adjustments, and interactions with other parts of the tax code. For precise results, use tax software or consult a tax professional.
Are the thresholds and 3.8% rate guaranteed to stay the same?: Tax laws can change. The thresholds and 3.8% rate in this calculator reflect current NIIT rules at the time of design. Always verify against current IRS guidance or professional advice, especially for future‑year planning.
Does this tool account for state or local taxes on investment income?: No. NIIT is a federal tax. States and localities may impose their own taxes on investment income, which are separate from the 3.8% NIIT and are not modeled here.
How should I enter capital gains and losses?: Enter your net investment income after considering capital gains and capital losses in aggregate. For example, if you have $40,000 in gains and $10,000 in losses, you might enter $30,000 as your net investment income for this simplified estimate.
Is the output from this calculator enough to file my taxes?: No. The output is an educational estimate only. Filing NIIT accurately requires following IRS instructions and potentially accounting for many details not captured here. Always rely on official IRS forms, tax software, and/or a qualified tax advisor for actual filing.

Related calculators

finance

Capital Gains Harvest Calculator

Estimate gain, tax, and net proceeds from harvesting capital gains at your tax rate.

finance

Underpayment Penalty Calculator

Estimate IRS underpayment interest on estimated tax shortfalls using a simple daily rate.

finance

Child Tax Credit Eligibility

Estimate child tax credit eligibility and phaseout based on AGI, filing status, and number of qualifying children.

This Net Investment Income Tax calculator offers a simplified 3.8% NIIT estimate based on user‑supplied net investment income, AGI, and filing status. It does not capture all NIIT rules, income classifications, or interactions with other tax provisions and is not intended as tax, legal, or financial advice. For actual tax filings and detailed planning, consult IRS guidance, tax software, and a qualified tax professional.