Introduction: Effectively Connected Income Turns a British Investor Into a US Taxpayer
Effectively connected income is income that a non-US person earns through a trade or business in the United States, and America taxes it on a net basis at the same graduated rates that apply to its own citizens. That single label changes everything. Without it, a British investor usually faces a flat withholding tax or no US tax at all. With it, you must file a US return, and rates climb to 37%.
Many wealthy Britons cross this line without noticing. For example, a stake in a US operating partnership, a membership interest in an LLC, or a building let in Florida can each create effectively connected income. Moreover, the tax often arrives as withholding on profits you never received.
However, most published guides stop at the US border. They do not explain the US-UK treaty, the deadline that can cost you every deduction, or how HMRC taxes the same profit. This guide covers all of it. TaxYork prepares US and UK returns for high-net-worth clients on both sides of the Atlantic, so we handle both halves of this problem together.
What Effectively Connected Income Is and Why the Label Matters
Effectively connected income versus passive income
Effectively connected income is one of two boxes into which America sorts the US income of a foreign person. The IRS sets out the basic rule on its effectively connected income page. The other box holds passive income, which the IRS calls fixed, determinable, annual or periodical income. That box covers dividends, interest, rents and royalties.
The two boxes are taxed in opposite ways. Passive income suffers a flat 30% on the gross amount, withheld by the payer, with no deductions. However, the US-UK treaty cuts that rate sharply. In contrast, business income is taxed on the net figure after expenses, but at graduated rates and on a filed return.
Therefore, the label decides three things at once. It decides the rate, whether you may deduct costs, and whether you must file. Notably, neither box is always better. A profitable business usually pays more as business income, while a leveraged property often pays less.
The first test: a US trade or business
Nothing is effectively connected income unless you are engaged in a trade or business in the United States during the year. However, the Internal Revenue Code never defines that phrase fully. Instead, the courts ask whether your US activity is considerable, continuous and regular. Occasional or passive activity does not count.
Section 864 fills in some edges. Performing services in America is generally a US trade or business. However, trading shares, securities or commodities for your own account is not, even through a US broker. Consequently, a British investor with a US brokerage portfolio does not have business income from it.
The second test: the connection
Once a US business exists, the question becomes which income belongs to it. For ordinary US-source business profits, the answer is automatic. All of it is effectively connected income. For investment-type income and gains, two tests apply instead. The asset-use test asks whether the income comes from assets used in the business. The business-activities test asks whether the business was a material factor in earning it.
Furthermore, timing does not rescue you. Income received in a later year is still connected if it would have been connected in the year you earned it. Hence, a deferred payment after you close the US business remains taxable.
How a British Investor Ends Up With Effectively Connected Income
Through a US partnership or LLC
This is the most common route by far. Under section 875, a partner is treated as engaged in a US trade or business whenever the partnership is. Your own activity is irrelevant. Therefore, a wholly passive British limited partner in a US operating business has effectively connected income on every dollar of allocated profit.
The same rule applies to an LLC taxed as a partnership. Moreover, it applies down a chain of partnerships. Consequently, a fund that holds an operating business through a partnership passes that character up to its investors. In practice, this is why many funds offer foreign investors a corporate blocker.
Additionally, a single-member LLC is ignored for US tax. As a result, its business is treated as yours directly. Our guide to Form 5472 for UK owners of a US LLC covers the separate reporting that such an LLC triggers.
Through US real estate
Property creates business income in two ways. First, a gain on US real estate is always treated as effectively connected income, whatever your level of activity. Those are the FIRPTA rules, and our guide to FIRPTA withholding on a US property sale explains them.
Secondly, rent can go either way. Rent from one passively held building is often passive income, taxed at 30% of the gross rent. That result is usually disastrous, because mortgage interest, repairs and depreciation earn no relief. However, section 871 lets you elect to treat the rent as business income. Importantly, the US-UK treaty contains no equivalent election, so you must make the domestic one on the return.
Through services performed in America
Work done on US soil is a US trade or business. Therefore, a British consultant who spends weeks with an American client can have effectively connected income from the fees. Nevertheless, a narrow statutory exception covers visits of 90 days or fewer where the pay is $3,000 or less. For most of our clients, that ceiling is irrelevant.
Instead, the treaty does the work. For employees, the employment article usually removes US tax on short visits. For the self-employed, the business profits article applies. Nevertheless, treaty relief does not remove the duty to file, as we explain below.
Through selling a partnership interest
A sale can create business income even where you expected a capital gain taxed only in Britain. Since 2018, section 864(c)(8) treats the gain on a partnership interest as effectively connected income to the extent the partnership's own assets would produce it on a sale. Furthermore, the buyer must withhold 10% of the price. Our article on section 1446(f) withholding on a partnership interest covers the mechanics.
How America Taxes Effectively Connected Income
Graduated rates for individuals in 2026
A non-resident individual pays tax on effectively connected income at the ordinary graduated rates. For 2026, those run from 10% to 37%, as the IRS inflation adjustments for 2026 confirm. The 37% rate begins above $640,600 for a single filer.
However, a married non-resident cannot file jointly. You must use the married filing separately schedule, where 37% begins above $384,350. Additionally, a non-resident receives no standard deduction. Therefore, tax starts on the first dollar of net business income.
Deductions, and the 20% business deduction
Net basis taxation means real deductions. You may deduct expenses that relate to the US business, including interest, wages, depreciation and state income tax within the federal cap. Moreover, long-term capital gains that count as business income still enjoy the lower capital gains rates, which top out at 20%.
One relief is often missed. The qualified business income deduction in section 199A applies only to income connected with a US trade or business. Consequently, a British investor's business income can qualify. The deduction is up to 20% of the qualifying profit, subject to wage and property limits at higher incomes. It does not cover most professional service businesses above the income thresholds.
Two taxes a non-resident does not pay
Two charges that burden American owners fall away. First, the 3.8% net investment income tax does not apply to non-resident aliens. Secondly, self-employment tax does not apply to them either. Therefore, the federal burden on a British partner is often lower than on an American partner with the same profit share.
Corporate rates and the branch profits tax
A British company with a US business is taxed differently. Its effectively connected income bears the flat 21% corporate rate, reported on Form 1120-F. Furthermore, section 884 adds a branch profits tax of 30% on after-tax profits that leave the US business. That second layer mimics a dividend.
Here the treaty helps greatly. The US-UK double taxation convention caps the branch charge at 5%, and removes it entirely for a company that meets its ownership and limitation on benefits tests. Accordingly, a qualifying UK company can run a US branch at 21% federal tax with no second layer.
State tax sits outside the treaty
Federal tax is only part of the bill. Most states tax non-residents on business income sourced there, and several charge entity-level fees as well. Importantly, the US-UK treaty does not bind the states. Therefore, treaty relief that removes federal tax leaves state tax in place. In practice, a partner in a multi-state business may need several state returns.
The US-UK Treaty and the Permanent Establishment Test
Business profits need a permanent establishment
The treaty replaces the domestic threshold with a higher one. Under the business profits article, America may tax a UK resident's business profits only where they are attributable to a permanent establishment in the United States. Specifically, a permanent establishment is broadly a fixed place of business or a dependent agent who habitually concludes contracts. The Treasury text of the treaty sets out both tests.
Consequently, a gap exists. Some effectively connected income under domestic law is exempt under the treaty. For instance, a British consultant who works at client premises for a few weeks has a US trade or business but usually no fixed place. Hence, the federal tax falls away.
A partnership's office is your office
The gap closes quickly for investors. Under long-standing IRS practice and case law, a partner is treated as having a permanent establishment wherever the partnership has one. Therefore, a passive British limited partner cannot argue that he or she has no US office. The partnership's premises are attributed to every partner.
Similarly, the treaty never protects gains or income from US real property. Those remain taxable in America under the real property and capital gains articles.
You must still file and disclose
Treaty exemption is a claim, not an absence of obligation. A non-resident engaged in a US trade or business must file a return even where the treaty exempts every dollar. Additionally, you must disclose the position on Form 8833. Under section 6712, the penalty for failing to disclose is $1,000 for an individual and $10,000 for a corporation.
Our guide to claiming a treaty position on Form 8833 explains the form. Our tax treaty optimisation service covers the wider claim.
Withholding: The Tax Is Collected Before You File
Section 1446 on partnership profits
America does not wait for a foreign partner to file. Under section 1446, a partnership must pay withholding tax on each foreign partner's share of effectively connected income. The rate is 37% for individuals and 21% for corporations. The IRS explains the system on its partnership withholding page.
Importantly, the tax is due whether or not the partnership distributes any cash. Furthermore, it is computed at the top rate with few deductions. As a result, the withholding nearly always exceeds the true liability. The partnership reports your share on Form 8805, which accompanies Form 8804. You recover the excess only by filing a return.
Form W-8ECI for other payers
Other payers face a different risk. A US customer who pays a foreign person must normally withhold 30%. However, that rule does not apply to business income. Therefore, you give the payer Form W-8ECI, which certifies that the payment is effectively connected income and that you will report it yourself. Additionally, the form requires a US tax number and remains valid for three calendar years.
FIRPTA and sale withholding
Sales carry their own regime. A buyer of US real estate from a foreign seller generally withholds 15% of the gross price under the FIRPTA withholding rules. In contrast, a buyer of a partnership interest withholds 10%. Both figures are prepayments, not final taxes. Consequently, a return is again the only route to a refund.
Filing: Form 1040-NR and the Deadline That Removes Your Deductions
Who files and when
An individual reports effectively connected income on Form 1040-NR. Where you have no US wages subject to withholding, the return is due on 15 June following the tax year. An extension is available on request. Additionally, you need an individual taxpayer identification number, which you obtain on Form W-7.
IRS Publication 519 contains the detailed rules. Our guide to Form 1040-NR for a British spouse with US income walks through the form itself.
The 16-month rule
One rule deserves particular attention, because few guides mention it. A non-resident receives deductions and credits only by filing a true and accurate return on time. Treasury Regulation 1.874-1 sets the outer limit at 16 months after the due date. For a foreign corporation, Regulation 1.882-4 sets it at 18 months.
Miss that limit and the IRS may tax your gross business income with no deductions at all. For a property investor with heavy interest and depreciation, the result can exceed the real profit. Moreover, where you have never filed before, an IRS notice can end the period even sooner. A waiver exists for good-faith cases, but it is discretionary.
Protective returns
The practical answer is a protective return. Where you believe you have no US trade or business, or that the treaty exempts the income, you can still file a return that reports no taxable income and explains why. Consequently, your right to deductions is preserved if the IRS later disagrees. We file protective returns routinely for clients with borderline US activity.
The UK Side: How HMRC Taxes the Same Profit
Worldwide income and credit for US tax
A UK resident pays UK tax on worldwide income, as GOV.UK explains in its guidance on tax on foreign income. Therefore, your US business profit appears on your Self Assessment return as well. Double taxation is then relieved by credit. HMRC allows the US federal tax on the same profit against the UK tax on it, and it generally allows US state income tax too.
However, the credit is capped at the UK tax on that income. Additionally, the years rarely match. The US works on the calendar year, while the UK year ends on 5 April. Hence, the profit must be apportioned, and the US tax matched to the right UK year.
Limited partnership or LLC: the choice that decides the UK bill
Entity choice matters more in Britain than in America. HMRC's list of foreign entity classifications treats a US limited partnership as transparent. Consequently, you are taxed on your share of profit as it arises, and the US tax is credited cleanly.
In contrast, HMRC generally treats a US LLC as opaque. It taxes you on distributions as dividends, not on the underlying profit. As a result, HMRC often denies credit for the US tax, because the two countries are taxing different income. Our guide to the US LLC as a hybrid entity for UK residents explains the problem in full.
The government consulted in summer 2026 on reforming the taxation of UK-resident members of US LLCs. However, a consultation is not law. Until legislation takes effect, the mismatch remains. Our article on the reverse hybrid reform for US LLCs tracks the proposal.
A UK company with a US branch
Where a UK company earns the profit, corporation tax applies at up to 25%, with credit for the US tax. Alternatively, the company can elect to exempt its foreign branch profits altogether. That election is irrevocable and also blocks relief for branch losses. Therefore, it needs modelling before you make it.
Case Study: A British Limited Partner in a US Operating Business
The facts
This illustrative example uses 2026 rates. James is a British national, resident in London, and has never lived in America. James is married and holds no green card. Additionally, he owns 30% of a US limited partnership that runs a logistics business from a state with no personal income tax. Notably, he takes no part in management.
For 2026, his share of the partnership's net profit is $600,000. Importantly, the partnership has an office and warehouses in America. Therefore, James has effectively connected income of $600,000, and the treaty offers no shelter, because the partnership's premises count as his permanent establishment.
The US tax
The partnership pays section 1446 withholding of 37%, which is $222,000. It reports that sum to James on Form 8805. However, his real liability is lower. The business qualifies for the 20% deduction and meets the wage limits, so his taxable income is $480,000.
On the married filing separately schedule, the tax on $480,000 is about $138,700. That is an effective rate of roughly 23% on the full profit. Consequently, James is due a refund of about $83,300. He receives it only by filing Form 1040-NR. Had he missed the 16-month limit, the IRS could have denied the deduction, and the refund would have shrunk sharply.
The UK tax and the entity lesson
In Britain, James pays income tax at 45% on the profit share, which is about $270,000 before allowances. HMRC credits the US tax of $138,700. Therefore, he pays roughly $131,300 more in the UK. His combined burden is 45%, which is simply the higher of the two rates.
Now change one fact. Suppose the business were an LLC that HMRC treats as opaque, and it distributed the after-tax profit of $461,300. The US tax is unchanged. In contrast, HMRC taxes the distribution at the 39.35% dividend rate, which is about $181,500, with no credit. As a result, the total reaches about $320,200, or 53% of the profit. The structure alone costs James roughly $50,000 a year.
How TaxYork Can Help
TaxYork provides comprehensive tax preparation and compliance for wealthy clients with income on both sides of the Atlantic. For a British investor with US business profits, we prepare Form 1040-NR, the treaty disclosure, the state returns and the matching UK Self Assessment entries. We also reconcile Forms 8805 and K-1 against the withholding, so that every dollar of prepaid tax is claimed.
Our cross-border planning service covers the preparation work that surrounds a US investment, including entity classification and foreign tax credit matching. In our experience, the costliest errors are the late first return and the unexamined LLC. Therefore, we review both before the first profit allocation arrives.
Conclusion
Effectively connected income is the point at which America stops treating a British investor as a passive outsider. From there, the US taxes your net business profit at graduated rates of up to 37%, collects much of it in advance through withholding, and expects a return every year. However, the system also gives real reliefs. Deductions, the 20% business deduction, lower capital gains rates and treaty protection all reduce the bill.
Above all, the reliefs depend on filing. A timely Form 1040-NR recovers excess withholding and preserves every deduction. Meanwhile, the right entity lets HMRC credit the US tax in full. Therefore, check the structure before you invest, file in the first year, and prepare the US and UK returns together.
Contact Us
If you hold, or plan to hold, a stake in a US business or property, the first US return sets the pattern for every later year. To have your US and UK filings prepared together, contact us today. You can also email hello@taxyork.com or call 020 3488 8606.
Disclaimer
This article provides general information only and reflects US and UK rules as understood in October 2026. It is not tax or legal advice for your circumstances. Whether income is connected with a US trade or business, and whether a permanent establishment exists, depends on the facts. The case study is illustrative, uses rounded figures and ignores UK allowances and National Insurance. Always obtain professional guidance from a qualified specialist before you invest or file.