Founders ask this in roughly the same words every time: my US LLC is making money, can I put some of it into a 401(k) and pay less tax? It is a reasonable question and the honest answer is a conditional yes. The condition is one concept that decides almost everything about how a foreign-owned US LLC is taxed, and most people meet it for the first time in the middle of this exact question.
The concept the whole question rests on: ECI
Effectively connected income, usually shortened to ECI, is income connected with the conduct of a trade or business inside the United States. It matters because the US taxes a non-resident two completely different ways depending on which bucket the income falls into.
Income that is not effectively connected, such as certain US-source dividends or royalties, is generally taxed at a flat 30% withheld at the source, with no deductions. Income that is effectively connected is taxed the way a US business is taxed: on net profit, at graduated rates, after you deduct your costs.
And a great many foreign-owned US LLCs have neither. If the company is not engaged in a US trade or business and has no US-source income, there is no US income tax to pay, which is exactly why the structure is popular. That situation is also the reason the 401(k) idea usually fails: if you owe no US tax on the profit, there is nothing for a deduction to reduce, and no US earned income to contribute from.
So the real question is: are you engaged in a US trade or business?
There is no single test and no dollar threshold. The IRS looks at whether your activity in the United States is considerable, continuous, and regular. In practice, the factors that push toward yes are:
- Employees or a dependent agent in the US acting on your behalf
- An office, warehouse, or other fixed place of business
- Inventory held inside the United States
- Sales activity conducted from within the US rather than from abroad
- Where title to the goods passes to the buyer
An independent service provider that has many clients and gives you a standardized service does not, on its own, create a US trade or business for you. A person who works only for you, follows your instructions, and depends on your business economically is a different matter.
The Amazon FBA complication
This is where a large share of our readers sit, and it deserves a straight answer rather than a comfortable one.
When you sell through Fulfillment by Amazon, your inventory is stored in US warehouses and remains yours until a US customer buys it, which means title passes on US soil. Combine that with sales that are continuous and regular, and many practitioners conclude the profit is effectively connected and therefore taxable in the US. Others argue Amazon acts as an independent agent and the seller is not engaged in a US trade or business.
This is genuinely unsettled. There is no ruling that closes it, positions differ between advisers, and a defensible answer depends on the specifics of your operation. What we will not do is tell you the comfortable version. If you sell FBA, treat ECI as a live question to get an answer on, not an assumption to build on.
The practical consequence cuts both ways. If you have ECI, you have a US filing obligation you may not have been meeting. You also, for the first time, have something a retirement contribution can actually reduce.
What you need before a Solo 401(k) is possible at all
Citizenship is not the barrier. Non-US citizens can and do have Solo 401(k) plans. The requirements are about the income, not the passport.
- US earned income that is effectively connected. Self-employment income from a US trade or business. Passive income does not qualify, and neither does profit that is not connected to a US business.
- A US tax return that reports it. For a non-resident that means Form 1040-NR with the business income on it. The contribution has to sit on top of income you are actually declaring.
- A US taxpayer identification number. An ITIN if you are not eligible for an SSN. This is a real timeline item, not a formality: expect weeks, sometimes longer from overseas.
- No full-time employees other than you and, if applicable, a spouse. A Solo 401(k) stops being available once you have a regular employee who qualifies.
- Contributions capped by your compensation. There is no minimum income, but you cannot contribute more than you earned.
Miss the first one and the rest is academic. That is the order to work through it in.
Why the order of operations matters more than the tactic
Almost everyone approaches this backwards. They read about the contribution limit, decide they want it, and then look for a way to qualify. Doing it that way tends to produce a structure built to justify a deduction rather than to reflect the business.
The sequence that holds up is the opposite:
- Establish whether your LLC has ECI. This determines your filing obligations, your tax rate, and whether any of the rest applies.
- Get compliant on what you already owe. A foreign-owned single-member LLC has a Form 5472 obligation whether or not it has income, and the penalty for missing it starts at $25,000. Optimizing a tax you are not correctly filing is the wrong way round.
- Then, if there is ECI and it is meaningful, look at whether a retirement contribution is the most efficient use of that money compared with reinvesting it in the business.
If you do not have ECI, what actually moves the number?
For a foreign owner with no US trade or business, the levers are not American retirement accounts. They are:
- Your own country's tax treatment of the profit, since that is where it is usually taxed. This is the biggest number in the calculation and it is decided outside the United States.
- Whether a tax treaty applies between your country and the US, and what it says about business profits and permanent establishments.
- How the entity is classified. A single-member LLC is disregarded by default. Electing corporate treatment changes the whole picture, sometimes for the better and often not.
- Pricing between related parties. If your US LLC buys from a company you own abroad, the price between them determines where profit lands, and it needs to be defensible.
- Not creating ECI by accident, which is a real risk when you hire in the US or start holding inventory there.
None of these is as satisfying as a contribution limit. All of them move more money.
The short version
A non-US owner of a US LLC can use a Solo 401(k), but only on US earned income that is effectively connected with a US trade or business, declared on a US return, with a taxpayer ID in hand. If your LLC has no ECI, the question is moot, because there is no US tax to reduce. If you sell through FBA, do not assume either answer. Find out.
This page describes how the rules work in general. It is not advice about your situation, and the ECI question in particular turns on facts that are specific to your operation. Take a position on it with someone who has looked at your numbers.
Want a straight answer on your own ECI position?
We work with foreign-owned US companies every week and the ECI question comes up in most of them. If you want someone to look at how your business actually operates and tell you where you stand, tell us about your setup.
Frequently asked questions
What is effectively connected income (ECI)?
Income connected with the conduct of a trade or business inside the United States. It is taxed on net profit at graduated rates after deductions, unlike non-connected US-source income such as certain dividends and royalties, which is generally taxed at a flat 30% withheld at source. Many foreign-owned US LLCs have neither, which is why they owe no US income tax.
Can a non-US citizen open a Solo 401(k)?
Yes. Citizenship is not the test. What matters is having US earned income that is effectively connected with a US trade or business, reporting it on a US return such as Form 1040-NR, holding a US taxpayer identification number, and having no full-time employees other than yourself and a spouse.
Does selling on Amazon FBA create effectively connected income?
It may. Your inventory sits in US warehouses and remains yours until a US customer buys it, so title passes in the US, and FBA sales are usually continuous and regular. Many practitioners treat that as effectively connected income. Others argue Amazon acts as an independent agent. The point is unsettled, so treat it as a question to answer with an adviser rather than an assumption.
My LLC pays no US tax. Can a 401(k) still save me money?
Not on US tax, because there is none to reduce, and you would not have qualifying US earned income to contribute from. Your profit is normally taxed where you are resident, so the saving would have to come from your own country's rules, not from a US retirement account.
What should I sort out before thinking about tax optimization?
Your existing filings. A foreign-owned single-member LLC files Form 5472 with a pro forma 1120 every year, including years with no revenue, and the penalty starts at $25,000. Establish your ECI position and get current on what you owe before optimizing anything.
Do I need an ITIN to contribute to a Solo 401(k)?
You need a US taxpayer identification number, which for someone not eligible for an SSN means an ITIN. Build real time into your plan for it, as applications from overseas commonly take several weeks and longer in filing season.
Sources: IRS guidance on effectively connected income and on being engaged in a trade or business in the United States; IRS one-participant 401(k) plan rules; Form 1040-NR and ITIN guidance. Current as of 27 July 2026. The treatment of marketplace fulfillment inventory is contested and no ruling settles it; verify your own position with an adviser.