How to Use This Calculator
- 1
Enter Total Net Investment Income
Input your total income from investments — interest, dividends, capital gains, and passive rental/royalty income.
- 2
Add Modified Adjusted Gross Income (MAGI)
Provide your total adjusted gross income plus any net foreign income, including wages, salaries, and other sources.
- 3
Specify the NIIT Threshold
Enter the income threshold for your filing status: $200,000 for single filers, $250,000 for married filing jointly.
- 4
Input the NIIT Rate
Enter the NIIT rate, currently 3.8%.
- 5
Review Your Results
The calculator displays your NIIT liability, income subject to NIIT, excess MAGI over the threshold, and effective NIIT rate. The insights panel shows a breakdown of taxable vs. non-taxable investment income and threshold gap analysis.
Example Calculation
A single filer with $50,000 in investment income and $240,000 MAGI wants to determine their NIIT liability.
Total Net Investment Income ($)
50,000
Modified Adjusted Gross Income ($)
240,000
NIIT Threshold ($)
200,000
NIIT Rate (%)
3.8
Results
Net Investment Income Tax
$1,520.00
Income Subject to NIIT
$40,000
Excess MAGI Over Threshold
$40,000
Effective NIIT Rate
0.63%
Tips
Use Tax-Advantaged Accounts to Shield Income
Contributions to 401(k)s, IRAs, and HSAs reduce your MAGI and can push you below the NIIT threshold. For example, a $23,000 401(k) contribution could save you up to $874 in NIIT alone.
Time Capital Gains Strategically
Spreading realized gains across tax years or using tax-loss harvesting can keep MAGI below the threshold. Use the NIIT table below to see exactly how different MAGI levels affect your tax.
Review Rental Income Classification
Passive rental income is subject to NIIT, but if you materially participate in a rental activity, it may be excluded. Consult a tax professional to determine your participation level.
Navigating Investment Income Taxes with the NIIT Calculator
The Net Investment Income Tax (NIIT) Calculator helps investors and taxpayers determine their liability under the 3.8% surtax on investment income.
When your Modified Adjusted Gross Income (MAGI) exceeds the statutory threshold, a portion of your investment income becomes subject to this additional tax.
In 2026, with investment portfolios growing and inflation pushing more earners above the fixed thresholds, calculating and planning for NIIT is essential for optimizing after-tax returns.
Why Understanding NIIT is Critical for Investors
For high-income investors, the NIIT represents a 3.8% additional levy on investment earnings that can meaningfully reduce after-tax returns.
The tax applies when MAGI surpasses $200,000 for single filers or $250,000 for married filing jointly.
Because these thresholds are not indexed for inflation, more taxpayers are affected each year.
Understanding your NIIT exposure allows you to strategically time capital gains, choose tax-efficient investment vehicles, and maximize contributions to tax-advantaged accounts — all of which directly impact long-term wealth accumulation and retirement readiness.
How to Calculate Your Net Investment Income Tax
The NIIT calculation compares your net investment income with the amount by which your MAGI exceeds the statutory threshold. The tax applies to the lesser of these two figures.
The calculation steps are:
- Calculate Excess MAGI:
Excess MAGI = MAGI - NIIT Threshold(if positive, otherwise 0) - Determine Income Subject to NIIT:
Income Subject to NIIT = MIN(Total Net Investment Income, Excess MAGI) - Calculate NIIT Owed:
NIIT Owed = Income Subject to NIIT x (NIIT Rate / 100)
`Total Net Investment Income` includes interest, dividends, capital gains, and passive rental/royalty income. `MAGI` is your Adjusted Gross Income with certain modifications. The `NIIT Threshold` is the IRS-defined income level for your filing status.
Worked Example: Determining NIIT Liability
Consider a single filer who wants to calculate their NIIT:
- Total Net Investment Income: $50,000
- Modified Adjusted Gross Income (MAGI): $240,000
- NIIT Threshold for Single Filers: $200,000
- NIIT Rate: 3.8%
Step-by-step calculation:
- Calculate Excess MAGI:
- $240,000 - $200,000 = $40,000
- Determine Income Subject to NIIT: The lesser of $50,000 (investment income) and $40,000 (excess MAGI):
- Income Subject to NIIT = $40,000
- Calculate NIIT Owed:
- $40,000 x 3.8% = $1,520
The individual owes $1,520 in NIIT. Note that only $40,000 of the $50,000 investment income is taxed because the excess MAGI ($40,000) is the limiting factor.
Strategic Tax Planning for Investment Income
Understanding NIIT enables strategic tax planning. Key strategies include using tax-advantaged accounts (401(k), IRA, HSA) to reduce MAGI, tax-loss harvesting to offset capital gains, and investing in municipal bonds whose interest is generally exempt from federal tax including NIIT. In 2026, the NIIT rate remains at 3.8% with thresholds fixed at $200,000 for single filers and $250,000 for married filing jointly. Because these thresholds are not inflation-adjusted, proactive planning is increasingly important for earners near these income levels.
The Affordable Care Act's Role in Net Investment Income Tax
The NIIT was introduced as part of the Affordable Care Act (ACA) in 2010, taking effect in 2013, to help fund healthcare reforms. Codified under IRS Code Section 1411, the tax imposes a 3.8% levy on the lesser of net investment income or excess MAGI above the threshold. The thresholds are fixed (not indexed for inflation), meaning more taxpayers are affected each year. Compliance requires careful tracking of investment income and MAGI, as miscalculations can lead to penalties and underpayment interest.
Frequently Asked Questions
What is the Net Investment Income Tax (NIIT) and who does it affect?
The NIIT is a 3.8% surtax on certain investment income that applies to individuals, estates, and trusts with income above specific thresholds. For single filers, the threshold is $200,000 MAGI; for married filing jointly, it is $250,000. The tax applies to the lesser of your net investment income or the amount by which your MAGI exceeds the applicable threshold.
What types of income are subject to the NIIT?
Income subject to NIIT includes interest, dividends, capital gains, rental and royalty income (if passive), and non-qualified annuity income. It also applies to income from passive business activities. Wages, salaries, unemployment compensation, Social Security benefits, and tax-exempt interest are excluded from NIIT.
How is the NIIT calculated?
The NIIT is calculated in three steps: first, compute the excess of your MAGI over the threshold (e.g., $240,000 - $200,000 = $40,000). Second, determine the lesser of that excess and your total net investment income. Third, multiply that amount by 3.8%. For example, with $50,000 in investment income and $40,000 excess MAGI, the NIIT is $40,000 x 3.8% = $1,520.
How can I reduce or avoid the NIIT?
Strategies include investing in tax-exempt municipal bonds, maximizing contributions to tax-advantaged retirement accounts (401(k), IRA, HSA), using tax-loss harvesting to offset capital gains, and carefully timing income recognition. These approaches can lower either your MAGI or your net investment income, reducing or eliminating NIIT exposure.
Are the NIIT thresholds adjusted for inflation?
No. Unlike many other tax provisions, the NIIT thresholds ($200,000 for single filers, $250,000 for MFJ) are fixed and not indexed for inflation. This means more taxpayers become subject to NIIT each year as incomes rise with inflation.