Selling a UK Business as a US Citizen: Tax on Both Sides

Reviewed by a CPA/EA and an ACCA-qualified accountant. Last updated: 19 August 2026.

Selling a UK business as a US citizen usually triggers capital gains tax in both countries: UK CGT on the disposal and US tax on the same gain, because America taxes citizens on worldwide income. The foreign tax credit relieves most double taxation, but reliefs like Business Asset Disposal Relief rarely align.

That misalignment is where the cost hides — in the reliefs, the deal structure, your filing history and the timing of the money.

Key takeaways

• One sale, two tax systems. The UK taxes the UK-sourced gain; the US taxes the same gain on citizenship grounds. You file in both.
• UK reliefs do not cross over. Business Asset Disposal Relief can cut your UK tax, but the US ignores it — and lower UK tax means less foreign tax to credit against your US bill.
• Structure drives the outcome. Selling shares versus the company selling assets changes the rate, the number of tax layers and whether Subpart F or GILTI is triggered.
• Your filing history is part of the deal. Prior Form 5471, GILTI and Subpart F reporting build earnings, previously taxed income and basis that shape the exit tax.
• Plan before heads of terms. Earn-outs and timing mismatches quietly break the foreign tax credit unless the deal is structured with both regimes in mind.

Why selling a UK business as a US citizen means tax on both sides

The UK asserts taxing rights because the company, its trade and usually its shareholders sit in the UK — a source-and-residence claim. The United States asserts taxing rights for a separate reason: citizenship. A US citizen is taxed on worldwide gains wherever they live, so a founder who has run a British company from London for fifteen years still has a US filing obligation the moment they sell.

The US-UK tax treaty does not simply switch one country off. Because of the treaty's saving clause, the United States generally keeps the right to tax its own citizens as though the treaty were not there, so relief from double taxation comes chiefly through credits, not exemption. The goal is not to file in only one country — it is to make the tax paid in one place credit cleanly against the tax due in the other.

Business Asset Disposal Relief: why it may not help your US bill

UK founders often build their exit around Business Asset Disposal Relief (the successor to Entrepreneurs' Relief), which can reduce the UK capital gains tax rate on qualifying disposals up to a lifetime limit, subject to shareholding, voting, trading-company and holding-period conditions. HMRC sets out the conditions and limits in its guidance on Business Asset Disposal Relief; confirm the live rate and lifetime cap before you rely on them, as both have moved in recent years.

Here is the cross-border sting. The United States does not recognise Business Asset Disposal Relief at all — to the IRS it is simply a lower rate of foreign tax. So when BADR reduces your UK bill, it also reduces the foreign tax available to credit against your US gain. If your UK tax after relief falls below the US tax on the same gain, a residual US liability appears — precisely because the UK relief worked. A relief designed to reward British entrepreneurs can, without planning, hand part of your proceeds to the US Treasury instead.

Share sale or asset sale — why the structure changes your tax

Most UK company sales are structured one of two ways, and for a US citizen the choice is not cosmetic.

• Share sale. You sell the company's shares and are generally taxed on a capital gain in both countries. This is usually the cleaner route for a US seller, but US rules can recharacterise part of the gain (see the next section).
• Asset sale. The company sells its trade and assets, which can create a UK corporate-level charge, and extracting the net proceeds can add a second layer. Worse, where the company is a controlled foreign corporation, an asset sale can throw off Subpart F or GILTI income taxable to you personally in the year of sale, independent of when you take the cash.

Buyers frequently prefer assets; US sellers frequently prefer shares. Bridging that gap is core deal work. Our cross-border business tax service exists to run exactly this comparison before the term sheet locks it in.

How your Form 5471 and GILTI history follows you into the sale

If you are a US citizen who owns a UK company, that company is very likely a controlled foreign corporation, and you have probably been filing Form 5471 every year, running GILTI and Subpart F calculations along the way. That history is part of the sale maths, not background paperwork.

On a share sale, US rules can recharacterise part of your gain as a dividend by reference to the company's accumulated earnings and profits, changing the rate and how the income is sourced for credit purposes. Meanwhile, amounts you have already been taxed on — previously taxed earnings and profits from prior GILTI and Subpart F inclusions — generally increase your basis or reduce the gain, so you are not taxed twice on the same profits. Getting this right depends on clean Form 5471 workpapers going back years; if your reporting has gaps, they surface at the worst possible moment. Our Form 5471 service is built around reconstructing and defending exactly these positions ahead of a disposal.

How the foreign tax credit relieves the overlap

For most US citizens selling a UK business that is not fully sheltered by UK relief, the foreign tax credit stops the same gain being taxed twice in cash terms. Broadly, you claim a credit against your US tax for the UK tax paid on the disposal, using Form 1116. Where the UK tax is at least as high as the US tax on the gain, the credit often extinguishes the US charge.

Three things decide whether it actually works:

• You must have paid or accrued the UK tax. If BADR or another UK relief wipes out the UK charge, there is nothing to credit.
• Timing must line up. The UK and US tax years differ, and UK tax may fall in a different period from the US gain. Aligning the two is central to a clean credit.
• Character and basket matter. Where part of the gain is recharacterised as a dividend, it can sit in a different credit category, and excess credits do not roam freely across baskets.

This is the interaction our cross-border tax calculator is designed to illustrate — and where sequencing the two filings, rather than treating them in isolation, earns its keep.

Earn-outs, deferred consideration and the timing trap

Modern deals rarely pay everything at completion. Earn-outs and deferred consideration are standard — and they are where the UK and US systems diverge most sharply.

The UK may treat the right to a future earn-out as an asset valued at completion, taxing later receipts as separate events. The US may instead spread or defer the gain under its own instalment-sale and contingent-payment rules, on a different timetable. So UK and US tax on the same pounds can land in different years — and when they do, the foreign tax credit can fail on timing alone, leaving US tax due in a year with no creditable UK tax paid, or vice versa. This is avoidable, but only if the earn-out is structured with both regimes in view before it is signed.

The bottom line

Selling a UK business as a US citizen is not one transaction but two parallel tax events planned together. UK reliefs like Business Asset Disposal Relief do not carry over to the US and can shrink your credit; the share-versus-asset choice changes the number of tax layers; your Form 5471 and GILTI history feeds directly into the exit; and earn-out timing can quietly break the foreign tax credit. Almost all of it is far easier to shape before heads of terms than to fix afterwards. Every position is reviewed and signed off by a licensed CPA/EA and an ACCA-qualified accountant before it reaches HMRC or the IRS.

Thinking of selling, or already in talks with a buyer? Book a consultation and we will model both sides of the deal before you commit.

This article is general information, not personalised tax advice. Rates, reliefs and lifetime limits change and depend on your circumstances; confirm your position with a qualified adviser before acting.