If you are a US citizen or Green Card holder selling a UK company, you are taxed twice on the same gain — once by HMRC and once by the IRS — and only the foreign tax credit stands between you and genuine double taxation. Business Asset Disposal Relief (BADR) reduces your UK rate to 18% on up to £1 million of lifetime qualifying gains for disposals on or after 6 April 2026. The IRS does not recognise BADR at all. Because a lower UK bill means a smaller foreign tax credit, part of every pound BADR saves you is simply collected by the US instead. Add the 3.8% Net Investment Income Tax, which no foreign tax credit can offset, and the arithmetic often surprises founders badly.
Why a US citizen selling a UK company faces two tax systems at once
The United States taxes its citizens and Green Card holders on worldwide income regardless of where they live. There is no exit from this by moving to London, and no threshold below which it switches off. If you are American and you sell shares in your UK trading company, that gain lands on a US Form 1040 in exactly the same way it would if you had never left Ohio.
The UK, meanwhile, taxes you as a resident on your worldwide gains. So a single disposal — one set of share purchase documents, one completion date, one wire transfer — generates two separate tax computations under two sets of rules that were never designed to speak to one another. They use different tax years, different definitions of a gain, different reliefs, different reporting deadlines and different currencies.
The mechanism that is meant to stop you paying the full amount twice is the foreign tax credit. It works, but only partially, and only if the sourcing and timing line up. Understanding where it fails is the whole game. Our guide to the foreign tax credit versus the FEIE covers the mechanics in general; this article deals with the specific case of a business exit, where the numbers are largest and the mistakes are most expensive.
What Business Asset Disposal Relief actually gives you on the UK side
BADR is the successor to Entrepreneurs' Relief. For qualifying disposals on or after 6 April 2026, it applies a reduced capital gains tax rate of 18%, subject to a lifetime limit of £1 million of qualifying gains per person. HMRC sets out the conditions in helpsheet HS275.
Outside BADR, the main UK capital gains tax rates for individuals are 18% and 24%, depending on how much of the gain falls within your unused basic rate band. For most people selling a business of any size, the gain comfortably fills the basic rate band and the marginal rate is 24%. So in practice BADR is worth up to six percentage points on the first £1 million of qualifying gains — a maximum UK saving of £60,000 per person.
One planning point that genuinely works on the UK side: spouses and civil partners are separate individuals for the £1 million lifetime limit. If both hold qualifying shares and both meet the conditions, two lifetime limits are available. That is real money, and it is one of the few structural advantages that survives contact with the US system — though only partially, as we will see.
Your unused basic rate band depends on your other income. For 2026-27 the UK Personal Allowance is £12,570, the basic rate band runs to £50,270, the higher rate band to £125,140, and the additional rate applies above that, per GOV.UK. You can model the UK side of a disposal with our UK capital gains tax calculator before you look at the American consequences.
The IRS does not recognise BADR — and never will
This is the point that catches founders and, frankly, a fair number of UK advisers. BADR is a domestic UK relief. It has no analogue in the Internal Revenue Code, no mention in the US-UK treaty, and no mechanism by which it flows through to a US computation. The IRS looks at your disposal, applies US rules to determine the gain, and applies US rates.
So the US calculates its own gain from scratch. Your cost basis is determined under US rules, not UK rules. Your holding period is measured under US rules. Any UK-specific reliefs, rebasing, share reorganisation treatments or deferral elections simply do not exist as far as the IRS is concerned. The two gain figures are frequently different, sometimes materially so, before you even get to rates.
For a high-net-worth seller, the US long-term capital gains rate is 20%. IRS Topic 409 confirms that the 20% rate applies to the extent taxable income exceeds the thresholds for the 15% rate — which a business sale of any size will do comfortably. On top of that sits the Net Investment Income Tax.
The 3.8% NIIT: the part no foreign tax credit can reach
The Net Investment Income Tax applies at 3.8% to net investment income above threshold modified adjusted gross income of $200,000 for single filers, $250,000 for married filing jointly, and $125,000 for married filing separately, per IRS Topic 559. Capital gains are net investment income. A business sale will breach these thresholds on completion day.
Here is the structural problem. The NIIT is imposed under a separate chapter of the Code from the regular income tax. Foreign tax credits under the standard rules offset regular income tax — they do not offset the NIIT. The Form 8960 instructions make this clear. That means 3.8% of your entire gain is payable to the US Treasury no matter how much UK tax you have paid on the same money. It is unrelieved double taxation by design.
For an American selling a UK business, this is usually the single largest irreducible cost of US citizenship in the transaction. On a £1 million gain it is £38,000 that no amount of planning on the UK side will recover. We go deeper on this in our article on the NIIT for Americans abroad.
Worked example: a £1 million business sale, both sides of the Atlantic
Let us make this concrete. Assume Sarah, a US citizen who has lived in London for twelve years, sells her UK trading company for a £1,000,000 gain. She has held qualifying shares for over two years, meets all BADR conditions, and has not used any of her lifetime limit. Her other income puts her firmly in the UK additional rate band and well above the US 20% and NIIT thresholds. We will run the figures in sterling for clarity — in reality the US computation is done in dollars, and the exchange rate movement between acquisition and disposal is a separate variable that can create or destroy gain on its own.
UK side. BADR applies to the full £1,000,000 at 18%. UK capital gains tax is £180,000.
US side. The gain is long-term. Regular US tax at 20% is £200,000. NIIT at 3.8% is £38,000. Total US tax before any credit is £238,000.
Foreign tax credit. Sarah's £180,000 of UK tax is available as a credit, but only against the regular US tax of £200,000 — not against the NIIT. So £180,000 offsets £200,000, leaving £20,000 of residual US regular tax. The £38,000 NIIT stands in full.
Result. Sarah pays £180,000 to HMRC and £58,000 to the IRS. Total tax on the gain is £238,000, an effective rate of 23.8%.
- UK CGT with BADR at 18%: £180,000
- US regular tax at 20%: £200,000
- Foreign tax credit available: £180,000
- Residual US regular tax: £20,000
- NIIT at 3.8%, uncreditable: £38,000
- Total combined tax: £238,000 (23.8% effective)
Now run the same sale without BADR — and see who actually benefited
Suppose Sarah did not qualify for BADR. Her UK rate would be 24%, giving UK tax of £240,000. Her US regular tax is unchanged at £200,000, fully covered by the credit — in fact she would have £40,000 of excess foreign tax credit with nothing to offset. The NIIT is still £38,000. Her total is £240,000 plus £38,000, or £278,000: an effective rate of 27.8%.
So BADR saved her £40,000 net, not the £60,000 it saved on the UK return. Roughly one third of the relief was quietly absorbed by the United States. Sarah did the work to qualify for BADR — the two-year holding period, the 5% shareholding, the officer or employee condition — and the IRS took a share of the reward.
That is the trap in its mildest form. It gets sharper. Where a seller's UK effective rate falls below the US effective rate on the same gain, every point of UK relief transfers directly to the US Treasury pound for pound. In the extreme case — a founder whose entire gain sits within the £1 million BADR band at 18% against a US cost of 23.8% — the UK relief does not reduce the total bill at all below 23.8%. It just changes which government collects.
Excess credits, baskets and the ten-year cliff
The no-BADR scenario above generated £40,000 of excess foreign tax credit. Founders often assume this is money in the bank for future years. Usually it is not.
Unused foreign taxes carry back one year and forward ten, and the carryover must be used within the same separate income category — the basket — that generated it. IRS Topic 856 and the Form 1116 instructions set out the categories: passive, general, foreign branch, section 951A, treaty-resourced and section 901(j) income. Excess credit in one basket cannot be used against a limitation in another.
A capital gain on a share disposal generally lands in the passive basket. So to use that £40,000, Sarah needs foreign-source passive income taxed by the UK at a rate above the US rate, in the passive basket, within ten years. If she sold her business and her remaining income is UK employment income or she has since moved back to the States, that will never happen. The credit expires unused after the tenth year and is gone permanently.
This is why excess foreign tax credits are a poor consolation prize. Planning that deliberately generates them — for example by declining a UK relief in the hope of banking credit — is usually value-destroying unless there is a concrete, modelled plan to absorb them.
The sourcing problem: is your gain even foreign-source?
Before you can claim a foreign tax credit at all, the income has to be foreign-source. For a foreign tax credit on a capital gain, this is not automatic and it is the most commonly missed technical point in the entire transaction.
Under US domestic sourcing rules, gain on the sale of personal property — including shares — is generally sourced by reference to the residence of the seller, and a US citizen is treated as a US resident for this purpose unless a specific tax-home and foreign-tax test is satisfied. If your gain is treated as US-source, there is no foreign-source income in the relevant basket, the Form 1116 limitation is zero, and the credit for your UK tax is zero. You pay the UK in full and the US in full.
Where domestic sourcing produces that outcome, the US-UK income tax treaty may resource the gain as foreign for credit purposes, which puts it into the treaty-resourced basket rather than the passive basket. This requires a treaty-based position and correct Form 1116 category reporting. Our overview of the US-UK tax treaty explains how resourcing articles work. Get this wrong and you do not lose a little — you lose the entire credit.
QSBS: why section 1202 will not save you
American founders often ask whether the qualified small business stock exclusion under section 1202 can shelter their exit. For a UK company, the answer is almost always no, and the reason is structural rather than technical.
Section 1202 requires the stock to be stock in a domestic C corporation — a corporation organised under the laws of a US state — that meets the active business and gross asset requirements. A company incorporated in England and Wales is not a domestic corporation. No election, no restructuring after the fact and no treaty provision converts it into one. The stock therefore cannot be qualified small business stock, and the exclusion is unavailable.
It is worth noting the rate consequence even where 1202 does apply: IRS Topic 409 states that the taxable part of a gain from selling section 1202 stock is taxed at a maximum 28% rate. For UK founders this is academic. The practical takeaway is that if you are an American who genuinely expects to build and sell a company, the entity choice you make at incorporation is one of the highest-value tax decisions of your life — and it is made years before anyone is talking about an exit.
Timing mismatches that create real cash-flow damage
The UK tax year runs 6 April to 5 April. The US tax year is the calendar year. A disposal completing on, say, 1 March 2027 falls in the UK 2026-27 tax year but the US 2027 calendar year. That single fact can put the UK tax and the US tax in different reporting years entirely.
The foreign tax credit is claimed either when foreign tax is paid or, if you elect, when it accrues. UK capital gains tax for a 2026-27 disposal is generally due by 31 January 2028 under Self Assessment. If you are on the cash basis for foreign tax credit purposes, the credit is not available until you actually pay — which may be a full year after you have had to file and pay the US return on the same gain. You fund the IRS in full first and recover through an amended return later.
The accrual election can align these, but it is a formal election with consequences that persist for future years and it interacts with the carryover rules. It should be modelled, not assumed. Either way, the practical planning point is blunt: hold back enough of the sale proceeds in cash to fund both tax bills at their respective due dates, and do not let the deal team persuade you that a rollover or reinvestment absorbs money you will need.
Earn-outs, loan notes and deferred consideration
Very few business sales are all cash on completion. Once you introduce earn-outs, deferred consideration or loan notes, the UK and US systems diverge again — and this time they diverge on when the gain arises, not just how much it is.
The UK has established treatments for ascertainable and unascertainable deferred consideration, and reorganisation provisions that can defer the charge on qualifying loan notes. The US has its own instalment sale rules and its own treatment of contingent consideration. They do not match. It is entirely possible to have a UK charge in one year and a US charge in a different year on the same slice of consideration.
Where that happens, you may have UK tax with no corresponding US tax to credit it against in that year, and US tax in a later year with no UK tax to credit. The foreign tax credit carryback of one year and carryforward of ten is the only bridge, and it is a narrow one given the basket restriction. Structuring an earn-out without modelling both systems in parallel is one of the most reliable ways to manufacture double taxation on an otherwise well-run deal.
The compliance layer people forget until it is too late
The tax on the gain is only part of the exposure. If you own a UK company as a US person, you have almost certainly had annual US information reporting obligations throughout the life of the business, and a sale tends to bring any historic gaps into sharp focus during due diligence.
Controlled foreign corporation reporting on Form 5471 is the main one, and the penalties for non-filing are severe and per-year. Our guide to Form 5471 for Americans with UK companies sets out who must file and what the categories mean. A buyer's advisers will ask about it. So will your own, if they are doing their job.
There are also foreign bank account and asset reporting obligations covering the proceeds once they land, and potential issues where the company has retained earnings that have already been taxed under US anti-deferral rules. Cleaning this up before a sale is dramatically cheaper than cleaning it up during one, when timelines are short and disclosure is unavoidable.
What actually helps: planning that survives both systems
There is no single move that eliminates the trap, but several reduce it materially — and almost all of them have to be made well before a sale process starts.
The most powerful is entity and jurisdiction choice at the outset, which is why this matters most to founders who are years away from an exit. After that come the spousal planning points, the timing of disposals relative to both tax years, and careful attention to sourcing and Form 1116 categories so the credit you are entitled to is actually claimed. Expatriation is sometimes raised, but it carries its own exit tax regime and is a life decision rather than a tax one.
What does not help is discovering the US position after heads of terms are agreed. By that stage the consideration structure is fixed, the timetable is set, and the only remaining variable is how much of the relief you earned on the UK side ends up in Washington. If you are dealing with property rather than shares, the analysis differs again — see our article on selling a UK home and US capital gains.
- Model both tax positions before agreeing deal structure, not after
- Check whether a spouse or civil partner can access a second £1m BADR lifetime limit
- Confirm the sourcing position and the correct Form 1116 basket in advance
- Consider disposal timing against both the UK and US tax year ends
- Reserve cash for two tax bills falling due at different dates
- Resolve any historic Form 5471 or foreign asset reporting gaps before due diligence
The bottom line
BADR is a genuine relief and you should claim it if you qualify. But for a US citizen it is worth substantially less than the headline suggests, because the foreign tax credit mechanism converts part of every UK saving into a US receipt, and because the 3.8% NIIT sits outside the credit system entirely.
In our worked example, a £60,000 UK relief delivered £40,000 of actual benefit and the combined effective rate never fell below 23.8%. That is the realistic floor for most American founders selling a UK company, and it can be considerably higher if sourcing is mishandled, if credits fall into an unusable basket, or if the timing of UK and US charges falls out of alignment.
None of this is a reason not to sell. It is a reason to know the number before you sign, and to build the tax position into the deal rather than discovering it afterwards.
