NIIT Foreign Tax Credit Optimizer: Claim Your 3.8% Refund Under US Tax Treaties [2026]

What Is the Net Investment Income Tax (NIIT)?

The Net Investment Income Tax (NIIT) is a 3.8% surtax on investment income for high-earning taxpayers. Congress created it in 2010 as part of the Affordable Care Act, and it took effect in 2013. The tax applies to individuals, estates, and trusts with income above specific thresholds.

The 3.8% Surtax Explained

The NIIT is a separate tax from your regular income tax. It is calculated as 3.8% of the lesser of:

• Your net investment income (NII), or
• The amount by which your modified adjusted gross income (MAGI) exceeds the applicable threshold

This means you only pay NIIT if both conditions are met: you have net investment income, and your MAGI is above the threshold. If either condition is not met, you owe no NIIT.

Who Pays NIIT? (Income Thresholds)

The NIIT thresholds depend on your filing status. These thresholds have not changed since 2013 and are not indexed for inflation.

If your MAGI is at or below these thresholds, you owe no NIIT regardless of your investment income. For most high-net-worth taxpayers with foreign investment income, the NIIT adds a significant tax burden beyond ordinary income tax.

What Income Is Subject to NIIT?

Net investment income includes the following categories, less allowable deductions:

• Interest — taxable interest income (excluding municipal bond interest)
• Dividends — both qualified and ordinary dividends
• Capital gains — net gains from the sale of property (excluding gains from active business)
• Rents — rental income, unless derived in the active trade or business of renting
• Royalties — from intellectual property, mineral rights, and similar sources
• Passive business income — income from S-corporations, partnerships, and LLCs where you are not materially participating
• Annuities — unless from qualified retirement plans

Key exclusion: Wages, salaries, self-employment income, Social Security benefits, and tax-exempt interest are not subject to NIIT.

For US expats and cross-border investors, foreign investment income is treated the same as domestic investment income for NIIT purposes. If you have foreign dividends, interest, capital gains, or rental income, the NIIT applies to it just as it would to US-source income.

Form 8960: How NIIT Is Calculated

You calculate and report NIIT on Form 8960, which is filed with your Form 1040. The form walks through:

1. Calculating your total net investment income (Part I)
2. Calculating your MAGI and the excess over the threshold (Part II)
3. Determining the NIIT amount (Part III)

The standard Form 8960 does not include a line for foreign tax credits. This is the core problem that treaty-based FTC claimants must address.

What Is the Foreign Tax Credit (FTC)?

The Foreign Tax Credit (FTC) is a dollar-for-dollar credit against your US income tax for income taxes paid to a foreign country. The purpose is to prevent double taxation — you should not pay tax twice on the same income, once to the foreign country and once to the US.

The FTC is governed by IRC §§27 and 901-909. It applies to individuals, corporations, estates, and trusts that pay foreign income taxes on foreign-source income.

How FTC Works

Unlike a deduction, which reduces your taxable income by your marginal tax rate (around 30-37%), a credit reduces your tax dollar-for-dollar. If you owe $10,000 in foreign taxes, you get a $10,000 credit against your US tax liability — provided certain limitations are met.

The FTC is not automatic. You must calculate it carefully and report it on Form 1116. The credit is limited to the amount of US tax attributable to your foreign-source income.

The FTC formula:

This limitation ensures the credit does not exceed the US tax you would have paid on the foreign income. If the foreign tax rate is higher than the US rate, you cannot claim a credit for the excess — though you may carry it forward for up to 10 years.

Form 1116: Claiming the Credit

Form 1116 is the primary form for claiming the FTC. Use our Form 1116 Slipover Calculator to compute your credit line by line. Key sections include:

• Part I — Foreign taxes paid or accrued
• Part II — Foreign-source income and expenses
• Part III — FTC limitation calculation
• Part IV — Summary of credits

For taxpayers with foreign investment income subject to NIIT, the FTC claimed on Form 1116 can potentially offset NIIT — but only under a treaty, as discussed later.

FTC Basket Categories (Passive vs. General)

The FTC uses a basket system to separate different types of foreign income. You must report income in the correct basket, and credits from one basket cannot offset tax from another basket. The most important baskets for NIIT purposes are:

Critical for NIIT planning: Passive-basket credits generally cannot offset general-basket tax. If you have passive foreign investment income, your FTCs must be allocated to the passive basket. This matters because NIIT applies to passive income — aligning your FTC basket with your NIIT exposure is essential for optimization.

FTC Carryforward: 10 Years

If your foreign taxes exceed the FTC limitation for a given year, you cannot use the excess credit that year. However, you can carry the unused credit forward for up to 10 years.

This creates a strategic opportunity: if you have a high-tax year abroad, you can generate excess credits that can offset future US tax, potentially including NIIT in future years. Track your carryovers with our Foreign Tax Credit Carryforward Calculator.

Carryforward credits are tracked on Form 1116, Schedule B, and must be applied in the order they were generated (first-in, first-out).

Deduction vs. Credit: Which Is Better?

You cannot claim both a credit and a deduction for the same foreign taxes. You must choose:

For most taxpayers with significant foreign investment income, the credit is superior because it provides a dollar-for-dollar benefit. The deduction only makes sense if you have minimal foreign taxes or if the MAGI reduction would eliminate your NIIT entirely. Compare both strategies side by side with our FEIE vs. FTC Optimization Engine.

The Problem: Why FTC Doesn't Normally Offset NIIT

If you have already tried to claim a foreign tax credit against your NIIT, you may have been told it is not allowed. That is because domestic FTC rules — the ones most tax software uses — do not permit it. Here is why.

Chapter 2A vs. Chapter 1 of the IRC

The Internal Revenue Code is divided into chapters. Two chapters matter here:

• Chapter 1 — "Normal Taxes and Surtaxes" (IRC §§1–1400). This is your regular income tax.
• Chapter 2A — "Net Investment Income Tax" (IRC §1411). This is the NIIT.

The Foreign Tax Credit under IRC §901 is designed to offset "income taxes" imposed by foreign countries. But the US tax code defines "income tax" in a specific way — and the FTC statute is located in Chapter 1, not Chapter 2A.

This creates a structural problem: the FTC was written to offset regular income tax, not the NIIT surtax. The IRS has consistently interpreted the law this way.

The IRS Position

The IRS position is clear and has been consistent for over a decade:

This means if you try to enter a foreign tax credit on Form 8960 using standard tax software, it will not work. The form has no line for it, and the IRS computers are programmed to reject any attempt to reduce NIIT with FTC.

The IRS has litigated this position. In Toulouse v. Commissioner (2021), the US Tax Court agreed with the IRS. The court held that the FTC cannot offset NIIT because Chapter 1 and Chapter 2A are separate.

The Double Taxation Problem for US Expats

Here is the problem this creates for US expats and cross-border investors. You earn investment income in a foreign country. That country taxes you. Then the United States taxes you again — both regular income tax and the 3.8% NIIT.

Your regular US income tax can be offset by the FTC. That part works. But the NIIT portion remains uncovered. If you have significant foreign investment income, this can mean paying tens or even hundreds of thousands of dollars in double tax.

Example: If you have $1,000,000 in foreign capital gains, the NIIT alone is $38,000. If your foreign country taxed you at 20%, that is $200,000 in foreign tax. Under the IRS position, you get the FTC against your regular US tax, but you still owe the $38,000 NIIT — even though you already paid tax to the foreign country.

This is not just unfair; it is the opposite of what most US tax treaties were designed to do. And that is where the legal breakthrough begins.

The Solution: Treaty-Based Foreign Tax Credits

Here is the breakthrough. While domestic law does not allow FTC to offset NIIT, a tax treaty may. US tax treaties are self-executing — they have the force of law without needing separate implementing legislation.

If a treaty defines "United States tax" broadly enough to include the NIIT, then the treaty's FTC provision can offset it. This is exactly what the courts in Bruyea and Christensen held.

Bruyea v. United States (2024) — The Canada Treaty Case

Paul Bruyea was a US citizen living in Canada. In 2015, he sold Canadian property and realized a $7,000,000 (CAD) capital gain. He paid $2,000,000 in Canadian tax and claimed a $1,400,000 FTC against his regular US tax.

But the IRS said he still owed NIIT on the gain. Bruyea challenged this in the US Court of Federal Claims. He argued that under the U.S.-Canada Tax Treaty, Article XXIV, the FTC should offset all US taxes — including NIIT.

The Court agreed with Bruyea. In December 2024, it held that the treaty's FTC provisions apply to "United States tax" — which includes the NIIT. The result? Bruyea is entitled to a refund of $263,523 in NIIT.

Christensen v. United States (2023) — The France Treaty Case

Before Bruyea, there was Christensen. In 2023, the same court held that the U.S.-France Tax Treaty, Article 24(2)(b) allows FTC to offset NIIT. The case established the legal framework that Bruyea later confirmed.

Christensen's case was similar: a US citizen living in France with investment income subject to both French tax and US NIIT. The Court held the treaty-based FTC could offset the NIIT.

Toulouse v. Commissioner (2021) — The Cautionary Tale

Not every court agrees. In Toulouse v. Commissioner (2021), the US Tax Court reached the opposite conclusion. The Tax Court held that the FTC cannot offset NIIT — period. This case did not involve a treaty claim, which is the key distinction.

This creates a jurisdictional split:

• Tax Court (Toulouse): No FTC against NIIT
• Court of Federal Claims (Christensen, Bruyea): Treaty-based FTC CAN offset NIIT

For taxpayers, this matters because where you file your claim can determine the outcome. If you file a refund claim and the IRS denies it, you can sue in either the Tax Court or the Court of Federal Claims. The Court of Federal Claims has been more favorable to taxpayers on this issue.

Case Comparison Table

What the Court Decisions Mean for You

If you live in Canada or France and have foreign investment income, you have the strongest case. The Bruyea and Christensen decisions are directly on point. You can file a claim for refund of NIIT already paid.

If you live in another treaty country, you may also have a case — but it has not been tested yet. You need to examine your specific treaty's language. Look for a phrase like "United States tax" or "all United States taxes." If your treaty includes the NIIT in its definition of tax, the same logic applies.

Pending Appeals: What's at Stake

The IRS has appealed both Bruyea and Christensen. They are now pending in the US Court of Appeals for the Federal Circuit:

• Bruyea: Fed. Cir. No. 25-1563 (docketed March 20, 2025)
• Christensen: Fed. Cir. No. 24-1284 (docketed December 22, 2023)

If the Federal Circuit upholds these decisions, the strategy becomes even stronger. If the Federal Circuit reverses, taxpayers who filed claims may face challenges. This is why the protective claim strategy is critical — it preserves your rights while the appeals are pending.

What you should do right now: Do not wait for the appeals to resolve. If your statute of limitations is approaching, file a protective claim immediately. You can always withdraw it later. You cannot get the time back.

Which Countries' Treaties Allow FTC Against NIIT?

Not all US tax treaties are the same. Whether your treaty allows FTC against NIIT depends on specific language in the treaty's definition of "United States tax" and its FTC provision. Browse our full International & Expat Tax Calculators hub for more cross-border tax tools.

Two treaties have been tested and proven in court: Canada and France. Other treaties may also work, but they have not been tested yet.

Canada (Bruyea) — The Strongest Case

The U.S.-Canada Tax Treaty, Article XXIV was at the center of the Bruyea case. The Court held that the treaty's FTC provision applies to "United States tax" — which includes the NIIT.

Why it works: The Canada treaty defines "United States tax" broadly, without limiting it to Chapter 1 taxes. This allowed the Court to conclude the NIIT is covered.

Who qualifies: US citizens or residents living in Canada who pay Canadian tax on investment income and owe US NIIT on the same income.

France (Christensen) — The Second Tested Treaty

The U.S.-France Tax Treaty, Article 24(2)(b) was tested in Christensen. The Court held the same principle applies: the treaty-based FTC can offset NIIT.

Why it works: The France treaty's language is similar to Canada's — it refers broadly to "United States taxes" without limiting to Chapter 1.

Who qualifies: US citizens or residents living in France who pay French tax on investment income and owe US NIIT on the same income.

Other Treaty Countries — What to Look For

If you live in another treaty country, you may still have a case. The key is the treaty's language. Look for these elements in your treaty's FTC provision:

• "United States tax" — broad language that does not limit to Chapter 1
• "All United States taxes" — includes both Chapter 1 and Chapter 2A
• Absence of "in accordance with" limitations — language that might limit FTC to Chapter 1

Treaties with potential for this strategy include:

How to Check Your Treaty

To determine if your treaty applies, follow these steps:

1. Find your treaty — US tax treaties are available on the IRS website.
2. Locate the FTC article — Look for the article that addresses double taxation relief (usually Article 20-25).
3. Read the language — Look for "United States tax" or "all United States taxes." If the treaty defines tax broadly, you have a strong case.
4. Look for limitations — If the treaty limits FTC to "taxes imposed under Chapter 1," it likely does NOT apply to NIIT.
5. Consult a professional — Treaty interpretation is complex. Work with a cross-border tax specialist before filing a claim.

How to Claim FTC Against NIIT: Step-by-Step Guide

This section walks you through the actual process of claiming treaty-based FTC against NIIT. No competitor provides this level of practical guidance — follow these steps carefully.

Step 1: Determine If You Qualify

Before you begin, confirm you meet these criteria:

• Your MAGI exceeds the applicable NIIT threshold ($200,000 single / $250,000 MFJ)
• You have foreign investment income (dividends, interest, capital gains, rents, royalties)
• You paid foreign tax on that income
• You are a resident of a treaty country with favorable language (Canada or France preferred)
• You are still within the statute of limitations for filing a claim

If you meet all five criteria, you have a viable claim.

Step 2: Gather Your Documents

You will need these documents:

• Your original tax return (Form 1040) for the year you are amending
• Form 8960 showing your NIIT calculation
• Form 1116 showing your FTC calculation
• Foreign tax returns and payment receipts (to verify foreign taxes paid)
• Investment statements showing foreign-source income
• The relevant tax treaty text
• Documentation of your country of residence

Keep copies of everything. The IRS may request supporting documentation.

Step 3: File a Protective Claim (Recommended)

A protective claim is a special type of amended return that preserves your right to a refund while the appeals are pending. It is the safest approach because:

• It stops the statute of limitations from running
• It does not require you to pay the tax again
• It preserves your position without committing to a final decision
• You can withdraw it later if the appeals go against you

How to file a protective claim:

1. Prepare Form 1040-X (Amended Return)
2. Include a statement that the claim is "protective" and is based on the Bruyea and Christensen decisions
3. Reference the specific treaty article you are relying on
4. State that you are preserving your rights pending the Federal Circuit appeals
5. File the claim before your statute of limitations expires

Step 4: File an Amended Return (1040-X)

If you have already paid the NIIT and are within the statute of limitations, you can file Form 1040-X to claim a refund. The amended return should:

• Include a corrected Form 8960 showing the reduced NIIT
• Include Form 1116 showing the treaty-based FTC
• Include Form 8833 (Treaty-Based Return Position Disclosure)
• Include Form 8275 (Disclosure Statement)
• Explain the treaty-based position and reference Bruyea/Christensen

Statute of limitations: You generally have 3 years from the date you filed your original return, or 2 years from the date you paid the tax, whichever is later. For most taxpayers, this means you can amend returns going back to 2021-2022.

Step 5: Complete Form 8833 (Treaty Disclosure)

Form 8833 is required whenever you take a treaty-based return position that overrides domestic law. You must complete it and attach it to your amended return.

Key sections to complete:

• Part I: Taxpayer information
• Part II: Treaty-based position — explain the specific treaty article you are relying on
• Part III: Description of the treaty position

For the NIIT-FTC claim, your description should reference Article XXIV (Canada) or Article 24(2)(b) (France) or the applicable article for your treaty.

Step 6: Complete Form 8275 (Disclosure Statement)

Form 8275 is a disclosure statement that can protect you from penalties. It is especially important for this claim because the IRS has publicly opposed it.

Filing Form 8275 reduces your risk of the substantial understatement penalty (20%). It signals to the IRS that you are taking a position that is contrary to their published guidance — but you are doing so in good faith based on court decisions.

What to include:

• A clear statement that you are relying on Bruyea and Christensen
• Citation to the specific court decisions
• Reference to the treaty article
• Note that the position is pending appeal

Step 7: Modify Form 8960

The standard Form 8960 does not include a line for foreign tax credits. To claim a treaty-based FTC against NIIT, you must modify the form. Here is how:

1. Calculate your NIIT liability as usual (Lines 1-17)
2. Add a new line below the NIIT calculation showing the treaty-based FTC
3. Subtract the FTC from the NIIT liability
4. Enter the reduced amount on the final line
5. Attach an explanation of the modification

Example modification:

You must clearly explain this modification in the attached statement. If the IRS questions the modification, you have a paper trail.

Step 8: Calculate Your Refund

Your potential refund is the difference between the NIIT you paid and the reduced NIIT after applying the treaty-based FTC.

Use the calculator on this page to estimate your potential savings. Enter your MAGI, foreign tax paid, NII, filing status, and treaty country to get an instant estimate.

If your estimated refund is substantial (say, over $5,000), the cost of professional assistance is likely worthwhile. If the refund is smaller, you may decide to handle it yourself with the guidance in this section.

Checklist for Filing

Before you file, verify you have everything: