What this calculator answers
This tool estimates the federal Net Investment Income Tax for an individual after the return-level amounts have been established. It answers one narrow question: how much of the supported net investment income enters the 3.8% calculation when compared with modified adjusted gross income above the filing-status threshold?
It does not decide whether a receipt belongs in net investment income, prepare Form 8960, calculate regular income tax, apply capital-gain rates, determine basis, or project a refund. Keeping those questions separate is important because the same transaction can affect several calculations in different ways.
The individual NIIT formula uses the smaller amount
For an individual, the federal tax equals 3.8% of the smaller of two figures: net investment income, or modified adjusted gross income above the applicable threshold. The calculator first subtracts the threshold from modified AGI, but not below zero. It then compares that excess with net investment income. The smaller non-negative amount is the NIIT base.
For example, a single filer with $230,000 of modified AGI and $100,000 of supported net investment income has $30,000 of modified AGI above the $200,000 threshold. The NIIT base is therefore $30,000, not $100,000, and the estimated tax is $1,140. If the same filer instead has $10,000 of net investment income, the $10,000 amount is smaller and the tax is $380.
2026 NIIT thresholds for individuals
The statutory threshold is $200,000 for single and head-of-household filers. It is $250,000 for married couples filing jointly and qualifying surviving spouses, and $125,000 for married individuals filing separately. These are not the standard deduction, ordinary-income brackets, capital-gain brackets, Medicare IRMAA brackets, or Additional Medicare Tax wage thresholds—even when some dollar amounts happen to match another rule.
Unlike many annual tax amounts, the NIIT thresholds are not automatically indexed for inflation. The calculator labels the estimate 2026 because the entered income and resulting tax belong to that tax year, while applying the current statutory individual formula described by the IRS. Always check the final 2026 Form 8960 and instructions before filing.
Modified adjusted gross income is not taxable income
Taxable income is calculated after deductions and is used in ordinary and preferential tax-rate calculations. NIIT modified AGI begins with adjusted gross income and applies the modifications required by Form 8960. Entering taxable income can understate the amount compared with the statutory threshold because the standard or itemized deduction generally comes later in the return.
For many individuals who do not exclude foreign earned income on Form 2555 and do not own relevant interests in controlled foreign corporations or passive foreign investment companies, Form 8960 modified AGI is the same as Form 1040 adjusted gross income. That common route is why the calculator allows a confirmed equal-to-AGI choice. The choice is a factual confirmation, not permission to assume the amounts are always equal.
What generally can be included in net investment income
Net investment income generally can include taxable interest, ordinary dividends, nonqualified annuity income, royalties, rents, income from passive activities, income from a trade or business of trading financial instruments or commodities, and net gain from certain property dispositions. The exact Form 8960 treatment depends on classifications, exclusions, modifications, related deductions, and how an activity is conducted.
“Net” matters. The final amount is not a brokerage account balance, gross sale proceeds, gross rent received, or a total copied from every Form 1099. Basis, capital-loss netting, activity-level expenses, allowed investment-interest expense, properly allocable deductions, and Form 8960 modifications can change the amount. The tool therefore asks for the supported final or projected net investment income amount instead of presenting a long wall of boxes that only imitates part of the official form.
Income that generally is not net investment income can still raise MAGI
Wages, unemployment compensation, Social Security benefits, tax-exempt interest, and most self-employment income generally are not themselves net investment income. Distributions from many qualified retirement plans and IRAs also are excluded from net investment income. But an excluded item can still increase adjusted gross income or modified AGI and use up threshold room, allowing a separate dollar of net investment income to become subject to NIIT.
A Roth conversion illustrates the distinction. A taxable conversion generally is not itself net investment income, but it can increase modified AGI. If the return also contains interest, dividends, passive income, or taxable capital gain, the higher MAGI can cause more of that separate net investment income to enter the 3.8% base. This is one reason to compare tax components without claiming that the conversion itself was taxed by NIIT.
Home-sale gain requires the exclusion calculation first
Gain from selling a personal residence that is excluded from gross income under the main-home exclusion is not subject to NIIT to the extent it is excluded for regular federal income tax. A potentially taxable remainder may still require Form 8960 analysis. Sale price and cash received are not the amounts to enter here.
Start with the 2026 Home Sale Capital Gain Calculator to separate amount realized, adjusted basis, gain, the supported Section 121 exclusion, and potentially taxable gain. Then establish the return-specific Form 8960 amount. The separate Home Sale Proceeds Calculator answers a cash-at-closing question and should not be used as a tax input.
Capital gains tax and NIIT are separate calculations
Eligible qualified dividends and net long-term capital gain can be taxed through the federal 0%, 15%, and 20% preferential bands. NIIT is a separate 3.8% tax that can apply in addition to regular income tax. A capital gain can therefore affect both calculations, but the bases and thresholds are not interchangeable.
Use the 2026 Long-Term Capital Gains Tax Calculator for the simplified preferential-rate calculation after basis, holding period, and loss netting are established. Do not add 3.8 percentage points to every capital-gain rate. The NIIT base is limited to the smaller of supported net investment income or excess modified AGI, so the effective incremental amount depends on the whole return.
NIIT and Additional Medicare Tax are not the same tax
The 0.9% Additional Medicare Tax generally concerns wages, Railroad Retirement Tax Act compensation, and self-employment income above applicable thresholds. NIIT concerns net investment income. A person can owe both taxes, but the IRS describes them as separate taxes applying to different types of income.
The standalone Additional Medicare Tax tool handles supported return-level Medicare wages and self-employment income. The 2026 Self-Employment Tax Calculator begins with one person’s supported business profit and reports only the Additional Medicare Tax attributable to that self-employment income. Neither result belongs in the net investment income box. Business income can involve special NIIT rules when an activity is passive, is a trading business, or has items excepted from self-employment income, so complete the applicable Form 8960 analysis.
Investment expenses and modifications require the official worksheet
Form 8960 has specific lines for investment-income categories, modifications, investment expenses, and deduction limitations. An expense being economically related to an investment does not automatically mean it is deductible in the NIIT calculation. Some deductions may already be reflected elsewhere, some require allocation, and some are not allowed for regular income tax or NIIT purposes.
Do not subtract advisory fees, custodial fees, state taxes, investment interest, rental expenses, capital-loss carryovers, or other amounts again merely because they seem investment-related. Use the current form and instructions to prevent double counting. Keep records supporting basis, activity classification, expense allocation, elections, carryovers, and the source of every included or excluded item.
Three useful boundary examples
Modified AGI does not exceed the threshold
A head-of-household filer has $200,000 of modified AGI and $45,000 of net investment income. Modified AGI above the $200,000 threshold is zero, so the NIIT base and estimate are zero. Having investment income by itself does not create tax when the second side of the “smaller of” comparison is zero.
Excess modified AGI is the limiting amount
A married couple filing jointly has $275,000 of modified AGI and $60,000 of net investment income. Modified AGI exceeds the $250,000 threshold by $25,000. The smaller amount is $25,000, producing an estimated $950 NIIT.
Net investment income is the limiting amount
A married-filing-separately taxpayer has $300,000 of modified AGI but only $20,000 of net investment income. The modified-AGI excess is $175,000, yet the NIIT base is limited to $20,000. The estimated tax is $760.
Payment timing can matter before the return is filed
NIIT is part of federal tax liability. The IRS notes that insufficient withholding or estimated payments can lead to an estimated-tax penalty. The NIIT estimate is not itself the quarterly payment because the payment calculation considers broader expected tax, credits, withholding, prior-year safe harbors, payment timing, and other rules.
After adding a supported NIIT amount to the broader projected total tax, use the 2026 Quarterly Estimated Tax Calculator for the standard cumulative safe-harbor comparison. Income received unevenly during the year, annualized-income methods, farmers and fishers, fiscal-year taxpayers, and special penalty exceptions require the official instructions rather than a simple quarterly split.
When this calculator intentionally stops
The simplified individual path stops for estates and trusts because their threshold and distribution rules differ. It also stops for nonresident and dual-status situations, U.S. territory issues, certain elections to file jointly with a nonresident spouse, foreign earned income exclusions, relevant CFC or PFIC interests, and unresolved return classification. Those facts can change whether NIIT applies or how modified AGI and net investment income are determined.
It also stops when the user has only salary, gross income, taxable income, sale proceeds, or an unverified investment total. A clean numeric answer from the wrong source is less useful than a clear next step. Complete or project Form 8960 through the required lines, then return with the supported amounts.
Why the calculator asks for two totals instead of twenty line items
A long list of boxes for interest, dividends, rents, royalties, annuities, business income, partnership income, capital gains, investment interest, state tax, losses, and modifications can look comprehensive while still omitting the rule that matters for a particular return. It can also invite users to copy gross amounts from information returns even when the official form requires netting, allocation, an exclusion, an election, or a value carried from another worksheet. More boxes do not automatically create a more accurate result.
The official Form 8960 is the right place to classify and reconcile those items. This calculator begins only after that work because the last individual computation is simple and useful: compare line 12 net investment income with modified AGI above the line 14 threshold. The four short steps make the source of each number visible, reject unsupported shortcuts, and let the user focus on the actual decision—whether net investment income, excess modified AGI, or neither is limiting the 3.8% base.
This design also makes scenario errors easier to spot. If a proposed transaction changes a brokerage gain by $40,000 but the supported Form 8960 net investment income changes by only $25,000 after loss netting and deductions, the calculator should receive $25,000—not the transaction headline. If the transaction raises modified AGI but the return remains below its threshold, the NIIT estimate remains zero even though regular federal or state income tax may increase.
Compare before-and-after Form 8960 amounts, not isolated transactions
For planning, create a baseline projection using the return as it stands. Then make one proposed change—such as realizing a gain, harvesting a loss, completing a Roth conversion, changing a rental activity, or selling a home—and recompute the applicable return worksheets. Enter the revised modified AGI and revised net investment income here. The difference between the two NIIT results is more informative than multiplying the transaction amount by 3.8%.
Suppose a single filer’s baseline has $195,000 of modified AGI and $30,000 of net investment income. The NIIT estimate is zero because modified AGI does not exceed $200,000. A separate $20,000 taxable retirement distribution might raise modified AGI to $215,000 while leaving net investment income at $30,000. The estimated NIIT becomes $570: 3.8% of the $15,000 MAGI excess. The distribution generally is not itself net investment income, so describing the result as a 3.8% tax on the distribution would be misleading.
Now suppose a supported capital loss reduces net investment income to $8,000 while modified AGI remains $215,000 after all return effects. The smaller amount becomes $8,000 and the estimate becomes $304. This is why a one-line shortcut based only on AGI, gain, or investment account value cannot reproduce the statutory comparison. Preserve both scenario worksheets so the reason for the difference remains auditable.
A practical record checklist
Retain the filed or projected Form 1040 and Form 8960, Forms 1099 and Schedules K-1, brokerage basis records, capital-loss carryovers, property settlement records, rental and passive-activity worksheets, investment-interest records, expense-allocation support, foreign-income and foreign-entity information, and documents supporting any exclusion or modification. Save the exact version of the official instructions used for the projection.
If planning a transaction, record both the facts before the change and the proposed facts after it. Compare supported Form 8960 amounts rather than assuming the transaction’s headline gain or distribution equals the change in NIIT. Rerun the broader tax and payment projection when wages, conversions, gains, losses, filing status, deductions, or other return items change.
Official sources and the 2026 filing caveat
The core formula, individual thresholds, broad income descriptions, home-sale exclusion treatment, and distinction from Additional Medicare Tax come from the IRS Net Investment Income Tax overview and Topic No. 559. The current detailed line definitions and special rules are in the Instructions for Form 8960, and the form landing page is About Form 8960.
As of July 27, 2026, the IRS instructions page available for detailed line guidance is the 2025 revision posted in 2026; the final 2026 revision was not identified. This calculator applies the current statutory individual formula for a 2026 planning scenario but does not predict later legislation, regulatory changes, form revisions, or individual guidance. Check the final 2026 form and instructions before filing.
This calculator provides educational federal arithmetic for a supported individual NIIT scenario. It is not tax preparation, tax, legal, accounting, investment, or financial advice. It does not determine residency, filing status, modified AGI, net investment income, basis, loss netting, activity classification, deductions, elections, regular income tax, capital-gain tax, Additional Medicare Tax, state tax, withholding, estimated payments, penalties, refund, balance due, or filing obligations. Verify every input and result with current IRS forms, instructions, records, software, and qualified guidance before filing, paying, selling, converting, or investing. Official sources were accessed July 27, 2026.