Net Investment Income Tax (NIIT) Calculator (2026)

§1411 imposes a 3.8% surtax on the lesser of (a) your net investment income or (b) your MAGI excess over the threshold. Thresholds are fixed by statute and not inflation-indexed: $200k single, $250k MFJ, $125k MFS.

Guidance, not advice. This calculator runs the rules as published, it doesn't assess your circumstances. Your actual tax may be affected by factors it doesn't cover (deductions, credits, filing status nuances, state-specific adjustments). Always seek financial or tax advice from a qualified CPA, Enrolled Agent, or tax attorney, or contact the IRS. Read our editorial scope →

Not inflation-indexed

The NIIT thresholds ($200k single / $250k MFJ / $125k MFS) are fixed by statute. They do not adjust for inflation. Each year, more taxpayers cross the threshold even without real income growth.

Filing status & MAGI

MAGI = AGI + excluded foreign income. Your MAGI determines the threshold.

Filing status

Modified Adjusted Gross Income (MAGI)

Same as AGI for most filers; add excluded foreign income if applicable.

Net Investment Income (NII) categories

Enter each category of investment income. The sum is your total NII.

Taxable interest

Savings, CDs, bonds

Dividends

Qualified and ordinary

Capital gains

Net gains ( LT + ST )

Passive rental income

Schedule E, not REP

Passive business income

Not materially participated

Annuities

Distributions (excess of basis)

Royalties

Intellectual property

Other NII

Trust/estate income, etc.

Total NII$73,000

What is not NII

These income types do not count toward NII.

W-2 wages and self-employment income (Schedule C)
S-Corp distributions (non-wage portion)
Partnership income where you materially participate
Social Security benefits
IRA / 401(k) distributions
Tax-exempt municipal bond interest
Excluded gain on sale of principal residence (§121)

NIIT owed

3.8% × lesser of NII or MAGI excess over threshold.

$2,774

Binding constraint: NII — the lesser of $73,000 (NII) and $80,000 (MAGI − threshold).

NIIT calculation walkthrough

Net Investment Income (NII)$73,000

MAGI$280,000

− Threshold (SINGLE)−$200,000

= MAGI excess$80,000

Lesser of (a) and (b)$73,000

× NIIT rate× 3.8%

NIIT$2,774

Real estate professional (REP) exclusion

If you qualify as a real estate professional and materially participate in your rental activity, that rental income is excluded from NII. You must meet the 750-hour test and the material participation tests under §469. This can significantly reduce or eliminate NIIT for real estate investors.

Tax year 2026 · USD · OBBBA permanent law

Formula: NIIT = 3.8% × min(NII, MAGI − threshold). Threshold: $200k single, $250k MFJ, $125k MFS.

Assumptions

Uses 2026 NIIT rate of 3.8% and fixed thresholds ($200k single / $250k MFJ / $125k MFS).
Thresholds are not inflation-indexed under current law.
MAGI for NIIT is generally AGI plus excluded foreign income (§911).
Does not model the 3.8% tax on undistributed S-corp or partnership income for passive investors (Regs. §1.1411-7).

Estimates only — not tax advice. Brackets, deductions and thresholds reflect the locked 2026 federal configuration. State amounts use each state's posted 2026 top-line rules and may differ from a full state-form computation. Always confirm complex situations with a qualified CPA, EA, or tax attorney.