Most taxpayers know about ordinary income tax rates and capital gains rates. Fewer understand the 3.8% Net Investment Income Tax (NIIT) — a separate surtax that can quietly increase your federal tax bill if your income exceeds certain thresholds.

This tax disproportionately affects:

• Real estate investors
• High-income W-2 earners with brokerage accounts
• Business owners with passive income
• Trusts and estates

Let’s break down what the law actually says.

The Law: IRC § 1411

The Net Investment Income Tax is codified at:

Internal Revenue Code § 1411

Under IRC § 1411(a)(1):

“There is hereby imposed… a tax equal to 3.8 percent of the lesser of—
(A) net investment income for such taxable year, or
(B) the excess (if any) of—
(i) the modified adjusted gross income for such taxable year, over
(ii) the threshold amount.”

This is not a marginal bracket.
It is an additional surtax layered on top of regular income tax.

Who Pays the 3.8% NIIT?

Under IRC § 1411(b), the threshold amounts are:

• $250,000 – Married Filing Jointly
• $200,000 – Single
• $125,000 – Married Filing Separately

If your Modified Adjusted Gross Income (MAGI) exceeds those amounts, NIIT may apply.

Important: These thresholds are not indexed for inflation.

What Counts as “Net Investment Income”?

Under IRC § 1411(c)(1), net investment income generally includes:

1. Interest
2. Dividends
3. Annuities
4. Royalties
5. Rents
6. Passive activity income
7. Net gain from disposition of property (capital gains)

But it does not include:

• W-2 wages
• Self-employment income
• Active business income
• Social Security benefits

Rental Real Estate and NIIT

Here’s where many landlords get surprised.

If rental activity is passive under IRC § 469, then rental income may be subject to NIIT.

However, if you qualify as a Real Estate Professional under IRC § 469(c)(7), your rental income may avoid NIIT because it is treated as non-passive.

This is a strategic planning issue — especially for married couples where one spouse materially participates in real estate.

Capital Gains and NIIT

Selling stock?
Selling rental property?
Selling a business interest?

If your income exceeds the threshold, that gain may be subject to:

• Regular capital gains tax (0%, 15%, or 20%)
• PLUS 3.8% NIIT

That means your effective federal rate on long-term capital gains can reach:

• 23.8% (20% + 3.8%)

Trusts and Estates Get Hit Harder

Under IRC § 1411(a)(2), trusts and estates are also subject to NIIT.

But their threshold is dramatically lower — it begins at the top bracket for trusts (which is reached very quickly).

This makes trust planning extremely important for high-net-worth families.

Planning Opportunities

Strategic planning may include:

• Timing capital gains
• Material participation planning
• Real estate professional election
• Installment sales
• Trust distribution strategies
• Charitable bunching
• Roth conversions in lower-income years

NIIT is not unavoidable — but ignoring it is expensive.

Why This Matters

Many taxpayers believe:

“My capital gains rate is 15%.”

But if your MAGI crosses the threshold, it may actually be:

15% + 3.8% = 18.8%

Or even:

20% + 3.8% = 23.8%

That difference adds up quickly on six- and seven-figure transactions.

Final Thoughts

The Net Investment Income Tax is one of the most misunderstood federal taxes. It affects investors, landlords, business owners, and trusts — often without warning.

If your income is approaching the NIIT threshold, proactive planning can make a significant difference.

At Dino Tax Co, we help clients navigate tax matters ranging from unfiled returns to IRS letters and levies and everything in between with clarity and confidence. If you’d like guidance on your situation, schedule a consultation today. Call or text (713) 397-4678 or email davie@dinotaxco.com. We’re here to help you take the next step.