What the US-UK Treaty Means When Starting a UK Business
The treaty means that starting a UK business still triggers full US reporting on your worldwide income, because the savings clause keeps American citizens taxable at home regardless of where the company is based. The treaty prevents double taxation through foreign tax credits, not through exemptions, and your choice of entity determines which IRS forms follow you every year.
By the TaxYork Cross-Border Tax Team — reviewed by a US-UK dual-qualified adviser (CPA / Enrolled Agent).
What does the treaty actually cover when starting a UK business?
The US-UK income tax treaty allocates taxing rights between the two countries and provides relief mechanisms, primarily the foreign tax credit, to prevent double taxation. It does not remove your US filing obligations, and it does not stop the IRS from treating your UK company as a reportable foreign entity. Understanding the treaty means that a UK business conversation starts properly with Article 1(4), the saving clause, which preserves the United States' right to tax its citizens and residents on worldwide income as if the treaty did not exist. The full US-UK tax treaty documents and the underlying technical explanation set out these articles in detail.
Articles 5 and 7 of the treaty deal with permanent establishments and business profits. A UK limited company's trading profits are taxable in the UK, not directly in the US, unless the company has a US permanent establishment. Where a US person then extracts value from that UK company, US rules on controlled foreign corporations step in separately, which is why the treaty on its own never tells the full story for a founder.
Why does the treaty mean starting a UK business differently depending on the entity type?
A US citizen setting up a UK Ltd, a UK LLP, or trading as a sole trader faces three completely different US reporting regimes, even though the UK tax treatment can look similar on the surface. This is the single most common misunderstanding we see from new clients, and it is exactly why the question of whether the treaty means starting a UK business needs an entity-first answer rather than a generic treaty overview. Choosing wrong at the incorporation stage often costs more in accountancy fees over five years than it would have cost to get proper advice upfront.
Is a UK limited company a CFC for US tax purposes?
Yes. A UK Ltd owned more than 50% by US shareholders, each holding at least 10%, is a Controlled Foreign Corporation under US rules, and that status follows the company for as long as the ownership test is met. This single fact is often the most important part of what the treaty means for starting a UK business for a majority US-owned company, because CFC status brings Form 5471 into play every single year.
Form 5471 has five filer categories, and penalties start at $10,000 per form per year, escalating up to $60,000 for continued non-filing after an IRS notice, as set out in the IRS's About Form 5471 guidance. The form itself demands detailed UK company accounts translated into US GAAP-style schedules, officer and director information, and a full computation of the CFC's earnings and profits.
NCTI has replaced GILTI from 2026 — what changes for a UK Ltd owner
From tax years beginning after 31 December 2025, the One Big Beautiful Bill Act renames GILTI to Net CFC Tested Income, or NCTI, and changes the mechanics that determine how much of your UK Ltd's profit gets swept into your US return. The Section 250 deduction drops from 50% to 40%, the foreign tax credit haircut improves from 80% to 90% of foreign taxes allowed, and the old 10% QBAI exemption for tangible assets disappears entirely. In practice, this means a profitable UK Ltd with a US majority shareholder faces a materially different calculation than it would have under the old GILTI regime, and older blog posts that still describe "GILTI" without mentioning NCTI are out of date.
A Section 962 election lets an individual US shareholder choose to be taxed on NCTI inclusions at corporate rates with indirect foreign tax credit access via Form 1118, which is worth discussing with your adviser once the UK Ltd starts generating real profit. It will not eliminate US tax, but it can materially change the timing of cash flow.
Can I use an LLC to start a business in the UK as a US citizen?
Technically, yes, but HMRC treats a US LLC as opaque, meaning it is taxed as a corporation in the UK with no check-the-box recognition of its US pass-through status. This classification mismatch is a genuine trap, separate from the core treaty-means-of-starting-a-UK-business question. Still, it catches out plenty of US citizens who assume their familiar home-state LLC will travel abroad cleanly.
UK residents have historically been denied UK double-tax relief on LLC distributions except in narrow circumstances following Anson v HMRC at the UK Supreme Court in 2015. HMRC's post-Anson guidance, last updated in December 2023, is fact-specific and does not hand out blanket relief, so do not assume your LLC structure automatically qualifies just because you have read about the case. A UK LLP with genuine multiple members is a cleaner alternative, reported via Form 8865 instructions rather than treated as an opaque corporation.
UK Ltd versus LLP versus sole trader for a US founder
Structure
UK treatment
US reporting form
Key US consequence
UK Ltd (majority US-owned)
Separate taxable company, Corporation Tax 19-25%
Form 5471
CFC status, NCTI inclusion possible
UK LLP (2+ members)
Tax-transparent partnership
Form 8865
Pass-through income, Category 3 contribution penalties possible
Sole trader (unincorporated)
Self-employment, Class 4 NIC
Form 8858
Disregarded entity reporting, possible SE tax exemption via totalization
Does the US-UK tax treaty prevent double taxation for a UK business owner?
It reduces double taxation through the foreign tax credit mechanism rather than exempting income outright, so UK Corporation Tax paid on your Ltd's profits generally offsets US tax on the same income once it flows through to you. This is the practical core of what the treaty means, starting with UK business owners who rely on it when planning cash extraction, dividends, or a Section 962 election.
UK Corporation Tax runs at 19% for profits up to £50,000, rising through marginal relief to a main rate of 25% above £250,000, figures confirmed unchanged for the financial year from 1 April 2026 in the Autumn Budget 2025 and published in full on the GOV.UK Corporation Tax rates page. The credit only works, however, if your US return properly reports the underlying foreign income and the foreign tax paid, which, for a CFC owner, means the 5471 schedules must be accurate before any credit claim makes sense.
VAT and registration realities that catch new founders out
The UK VAT registration threshold is £90,000 of taxable turnover on a rolling 12-month basis, unchanged for 2025/26 and 2026/27 after rising from £85,000 in April 2024, and you have 30 days to register once you cross it. Since 18 November 2025, all UK company directors and persons with significant control, including overseas US directors, must complete identity verification under the Economic Crime and Corporate Transparency Act 2023, as explained on GOV. UK overseas company registration page. There is no residency or visa requirement to be a sole director and shareholder of a UK Ltd, so a US citizen can incorporate from home before ever setting foot in the UK.
Do I need to file Form 5471 for a UK limited company?
If you are a US person who owns 10% or more of a UK Ltd that is majority US-owned, you almost certainly fall into one of the five Form 5471 filer categories and must file Form 5471 annually with your Form 1040. Missing this is one of the most expensive mistakes a new founder can make, since penalties start at $10,000 per form per year and climb from there.
A UK LLP with two or more genuine members is generally treated as a pass-through partnership for US purposes, which shifts the filing obligation to Form 8865 instead, carrying the same $10,000 starting penalty but different category rules, including a Category 3 contribution penalty of 10% of fair market value capped at $100,000 unless the failure is intentional. A UK sole trader operation, meanwhile, is reported on Form 8858 as a foreign disregarded entity or branch, again at the same $10,000 base penalty tier.
Is it better to set up a UK Ltd or a sole trader as a US expat starting a business?
There is no universal answer, but the honest starting point for most solo founders weighing this decision is that a sole trader structure is administratively lighter on the US side and is filed via Form 8858. At the same time, a UK Ltd offers limited liability and easier UK investment raising at the cost of Form 5471 and potential NCTI exposure. Founders who plan to keep profits modest and reinvest personally often start as sole traders and incorporate later, once turnover justifies the extra compliance. Founders raising UK investment or hiring UK staff almost always need a limited company from day one, notwithstanding treaty considerations.
Do I still pay US self-employment tax if I'm self-employed in the UK?
Generally, no, provided you are UK-resident and operating as a genuine UK sole trader, because the US-UK Totalization Agreement exempts you from US self-employment tax on that income once you hold a Certificate of Coverage from HMRC confirming Class 4 National Insurance is being paid instead. This exemption is narrow, though, and understanding exactly what the treaty means by starting a UK business as a sole trader helps avoid assuming it covers more than Social Security and Medicare, a point the IRS guidance on self-employment tax abroad makes clear.
Federal income tax on your worldwide self-employment profit still applies in full via the saving clause, so the totalization exemption only ever removes the 15.3% self-employment tax layer, not the underlying income tax liability. You still need the Foreign Tax Credit or, less commonly for a growing business, the Foreign Earned Income Exclusion to manage that income tax exposure.
Visas for US founders relocating to run the business
The old Tier 1 Entrepreneur visa closed to new applicants in March 2019, and any current content that still cites it, or the old £200,000 or £50,000 investment thresholds, is simply wrong. The relevant route today is the Innovator Founder visa, which carries no minimum investment requirement and allows settlement after three years, making it the realistic option for a US citizen who wants to run the UK Ltd hands-on rather than remotely.
Case study. A Seattle-based software consultant, Marcus, incorporated a UK Ltd in early 2025 to serve a growing roster of London clients, keeping 100% ownership himself. His accountant flagged CFC status immediately, given his sole ownership exceeded the 50% US-shareholder threshold, and Form 5471 Category 4 and 5 filings were added to his US return that year. When his UK Ltd's profits reached roughly £180,000 in year two, his adviser modeled a Section 962 election against the new NCTI rules, comparing it with simply taking a larger UK salary to reduce the CFC's tested income. He also discovered, mid-process, that his old California LLC used for prior consulting work had unreported foreign account balances dating back three years, and rather than panic, he used streamlined filing to catch up on unfiled US returns via streamlined filing to regularise that history before the new UK Ltd's first US return was due. Six months later, he applied for the Innovator Founder visa to relocate permanently, a step his adviser noted made sense only once his US compliance was fully current.
Founders making this decision from a house move rather than a pure business launch often benefit from considering the broader cross-border tax picture when relocating to the UK, alongside the entity-choice analysis above. Once the UK Ltd becomes genuinely profitable, most owners also need to decide between the Foreign Tax Credit and FEIE, since the two reliefs cannot be claimed on the same income. If you already have undisclosed foreign business income from before incorporation, streamlined filing may apply before you formalize the UK company, which is worth reading before your first UK Ltd accounts are filed. Founders who still hold unexercised US employer equity should also consider how founders exercising equity from a former US employer handle the overlap. Anyone considering an eventual return to the US should consider what happens to their compliance options if they later move the business back to the US, and those with older unfiled US returns predating the business will find that catching up on unfiled US returns via streamlined filing is relevant background reading.
Get treaty-aware structuring advice before you incorporate.
Choosing between a UK Ltd, an LLP, or sole trader status is far easier to get right before incorporation than to unwind afterward, and this is exactly where TaxYork's cross-border team adds the most value for a founder weighing what the treaty means when starting a UK business against real IRS deadlines. We model Form 5471, Form 8865, and Form 8858 outcomes side by side against your expected UK profit, so you can see the Section 962 election, NCTI exposure, and totalization relief laid out in actual numbers rather than theory. Contact us before you file at Companies House if at all possible, since some elections and structuring choices are far harder to change retroactively than to plan correctly from the outset.
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