Accidental American Selling a UK Company: Buyer Due Diligence

If you are an Accidental American selling your UK company, the US taxes the gain on your shares even though you are UK resident. Business Asset Disposal Relief does not exist in US law, but the UK CGT you pay is usually creditable. The usual order is to catch up prior-year returns, FBARs and Forms 5471 through the Streamlined Foreign Offshore Procedure, then report the sale year on time.

This guide is for UK-born founders whose US citizenship (by birth in the US, or through a US parent) has come up mid-transaction. It might arrive as a buyer's W-9 request, a citizenship question in completion KYC, a FATCA self-certification from the bank receiving the proceeds, or a warranty in the share purchase agreement. At Jungle Tax we prepare the US and UK returns that put this right. What follows covers what discovery means for the deal, which numbers actually move, and how the compliance work fits around completion.

How does US citizenship usually surface during a UK company sale?

Very few founders find this out from the IRS. On a UK exit it normally comes up through one of five routes:

• Buyer KYC and anti-money-laundering checks. The buyer's solicitors, or the corporate finance house, ask for passports, places of birth and nationalities. A US place of birth on a British passport is enough to start the conversation.
• A W-9 or W-8BEN request. US acquirers, US private equity funds and US paying or escrow agents routinely ask each seller to certify their US or non-US status for information reporting and backup withholding. A US citizen cannot honestly sign a W-8BEN. The right form is a W-9, and that needs a US Social Security Number.
• FATCA self-certification. Under the UK's implementation of FATCA, the bank or wealth manager receiving the completion monies has to establish whether you are a US person and, if you are, report the account to HMRC for onward exchange with the IRS.
• Tax warranties and disclosure. Well-advised buyers ask whether any seller is a US person, because it affects how the company's past US-facing filings and elections should be read.
• W&I insurance underwriting. Underwriters ask questions that put the point in writing.

Whichever route it takes, the facts are now on record with a counterparty, an adviser and possibly a bank. That should shape how the remediation is planned. Being discovered by a buyer does not by itself make your past non-filing wilful. Ignoring it once you know is a different matter, so the time to act is now.

Does the buyer inherit your US tax problem?

Generally, no, and saying this clearly calms most negotiations. Your US filing obligations are personal. Form 5471, FBARs, Form 8938 and your Form 1040 are filed by you as the shareholder, not by the company. A UK trading company with no US trade, US subsidiaries or US-source income does not normally take on US tax liabilities because one of its shareholders is a US citizen.

There are three exceptions the buyer's tax diligence will want to rule out:

• US operations. If the company has a US subsidiary, US employees, US-source income or a US branch, it may have its own US filing history to review, whoever its shareholders are.
• Entity classification elections. If anyone ever filed a US check-the-box election (Form 8832) for the company, its US tax character may differ from what the buyer assumes.
• A US buyer. A US acquirer will have its own US reporting on the target from completion. It will want to know whether the company has been treated as a controlled foreign corporation (CFC) in the past.

In practice, buyers want reassurance that the issue is personal to the seller, being handled by a qualified preparer, and will not delay completion or require price retentions. That is a compliance question, and well-organised compliance answers it.

How the US taxes your share sale (and why BADR does not help)

As a US citizen you are taxed on worldwide income wherever you live. The US-UK tax treaty contains a "saving clause" that keeps the US right to tax its own citizens as if the treaty did not exist, with limited exceptions. The sale of your shares is therefore a taxable event in both countries.

The UK side

As a UK resident you pay UK capital gains tax on the disposal. If you qualify for Business Asset Disposal Relief, gains up to the £1 million lifetime limit are taxed at a reduced rate: 14% for disposals in 2025/26, rising to 18% for disposals on or after 6 April 2026. Gains above the limit are taxed at the main higher rate of 24%. UK CGT is payable by 31 January after the end of the tax year of disposal.

The US side

The US calculates the gain separately, in US dollars, under US rules. Several differences matter:

• No BADR equivalent. US law has no counterpart to Business Asset Disposal Relief. The full US-computed gain is taxable.
• No QSBS exclusion. The Section 1202 qualified small business stock exclusion, which many US founders rely on, applies only to US C corporations. A UK limited company does not qualify.
• Long-term capital gains rates. Shares held for more than a year are taxed at a top federal rate of 20%. The 3.8% Net Investment Income Tax may apply on top.
• Dollar-based gain. Your base cost is translated at the exchange rate on the date you acquired the shares, and the proceeds at the rate on the date of sale. If sterling has weakened against the dollar since you founded the company, the US gain can be noticeably smaller than the UK gain, and the reverse is also true.
• Section 1248. If the company was a CFC at any time in the five years before the sale while you held 10% or more, part of the gain may be recharacterised as a dividend, to the extent of the company's untaxed earnings and profits. For an individual selling a UK company, the dividend may still qualify for the 20% qualified dividend rate. It also changes how the foreign tax credit is computed.

The foreign tax credit: where double taxation is mostly removed

The US gives a foreign tax credit for UK CGT paid on the same gain. For a US citizen whose tax home is in the UK and who pays at least 10% foreign tax on the gain, US sourcing rules generally treat the gain as foreign-source, so the credit can be used against it. In most founder exits the result looks like this:

• On the slice taxed in the UK at 24%, the UK tax exceeds the 20% US rate, so the US federal capital gains tax on that slice is generally eliminated and excess credits may carry forward.
• On the BADR slice taxed at 14% or 18%, there may be a small residual US liability, roughly the gap up to 20%.
• The 3.8% Net Investment Income Tax is the main exposure. The IRS takes the position that foreign tax credits cannot offset NIIT. Courts have reached different conclusions under different treaties, so any treaty-based position should be taken only on a properly prepared return with full disclosure.

Gain on stock in a foreign corporation is generally net investment income however active you were in the business. The material participation exception that protects active owners of US partnerships and S corporations does not apply to a UK limited company.

US vs UK treatment of the same share sale

Issue	UK (HMRC)	US (IRS)
Basis of taxation	Residence: UK residents taxed on worldwide gains	Citizenship: US citizens taxed wherever they live
Headline rate on founder shares	14% (2025/26) or 18% (from 6 April 2026) with BADR on first £1m; 24% above	Up to 20% long-term capital gains, plus 3.8% NIIT where applicable
Founder relief	Business Asset Disposal Relief, £1m lifetime limit	None for a UK company; Section 1202 QSBS unavailable
Currency	Gain computed in sterling	Gain computed in US dollars at historic and disposal-date rates
Earnings recharacterisation	Not applicable to an ordinary share sale	Section 1248 may treat part of the gain as a dividend where the company was a CFC
Double tax relief	UK has primary taxing right as residence country	Foreign tax credit for UK CGT; NIIT credit disputed
Share-for-share consideration	Rollover typically available under UK reorganisation rules	Deferral only if US reorganisation rules are separately met
Deferred consideration / earn-out	Marren v Ingles treatment for unascertainable earn-outs	Installment method or open-transaction analysis; timing can differ from UK
Return and payment	Self Assessment; CGT due 31 January after tax year end	Form 1040 due 15 April, automatic extension to 15 June for taxpayers abroad, further extension to 15 October

What prior-year filings are likely to be missing?

A founder who has never filed US returns usually has a backlog well beyond the sale itself. Here is what we usually find.

Form 5471 for the company being sold

A US citizen who owns 10% or more of a foreign corporation is generally required to file Form 5471 with their Form 1040. Which schedules apply depends on the filer category. Category 4 or 5 generally applies if the company is a CFC, and Category 3 covers the year in which a 10% interest is acquired or disposed of, so the sale year itself carries a 5471 obligation. The penalty for failing to file is $10,000 per form per year, with continuation penalties of up to a further $50,000 after IRS notice. There is a second, often overlooked cost: if a required Form 5471 is missing, the assessment period for the entire return can stay open, not just the items relating to the company.

CFC income inclusions

If US persons owning 10% or more together hold more than 50% of the company, it is a CFC. That can trigger annual US income inclusions on undistributed profits under the regime formerly known as GILTI (renamed net CFC tested income from 2026). For a profitable UK trading company paying corporation tax at 25%, or at 19% on small profits, the high-tax exclusion election is often available because the UK rate exceeds the US threshold. That can remove the inclusion, but only if the election is made correctly on the returns. A sole founder who is a US citizen almost always owns a CFC.

FBARs and Form 8938

An FBAR is required where the aggregate maximum value of your foreign financial accounts exceeds $10,000 at any point in the year. That includes accounts you have signature authority over, such as the company's own bank accounts. Founders often miss this, because they assume the company's accounts are the company's business. Form 8938 has separate, higher thresholds for taxpayers living abroad. You can model your exposure with our FBAR penalty calculator.

Personal investments: ISAs, pensions and funds

ISAs have no US tax shelter, so their income and gains belong on your US return. Stocks and shares ISAs, and general investment accounts holding UK or Irish funds, frequently contain passive foreign investment companies (PFICs) that require Form 8621 and punitive default tax treatment. UK pensions usually get more favourable treatment under the treaty, but they still need reporting. Your company shares are generally outside the PFIC regime while the company is a CFC and you are a US shareholder. If US persons hold 50% or less and the company keeps a large cash balance, PFIC testing becomes relevant.

How the Streamlined Foreign Offshore Procedure is sequenced around completion

The IRS Streamlined Filing Compliance Procedures exist for exactly this kind of non-wilful non-compliance. The foreign version suits UK-resident founders. It requires three years of delinquent or amended US returns, six years of FBARs, and a signed Form 14653 certification of non-wilful conduct with a detailed personal narrative. Taxpayers who qualify are not charged the miscellaneous offshore penalty, nor the failure-to-file, information-return or FBAR penalties covered by the programme. Tax and interest on the three years are still payable.

Eligibility requires that, in at least one of the three most recent years covered, you had no US abode and were physically outside the US for at least 330 full days. You must not be under IRS examination. The procedure must also be used before the IRS contacts you.

A practical timeline

1. Immediately: secure an SSN. Many accidental Americans have never had a Social Security Number. US citizens must use an SSN, not an ITIN, on streamlined returns, and you will need one to sign a W-9 truthfully. Applications through the US Embassy can take weeks, so start this before anything else.
2. Weeks 1-3: data gathering. Collect statutory accounts and corporation tax computations for the company for at least the last three to six years, share register history, original subscription cost, all personal bank, ISA, pension and investment statements, and your UK Self Assessment returns.
3. Weeks 3-8: prepare the streamlined package. Three years of Form 1040 with Forms 5471, 8938, 8621 and 1116 as needed, six FBARs filed electronically with FinCEN, and the Form 14653 narrative. The three years are the most recent ones whose due dates, including extensions, have passed. A sale completing in 2026 therefore normally falls outside the streamlined years.
4. Before or shortly after completion: submit. Ideally the streamlined package is filed before completion, or as soon as possible after it, so that the sale-year return is filed onto a clean compliance history.
5. The sale year: file on time. Report the disposal on a regular, timely Form 1040 with Form 8949, Schedule D, Form 1116 (foreign tax credit), Form 8960 (NIIT) and the Category 3 Form 5471. The UK CGT figure feeds the foreign tax credit, so UK and US computations should be prepared together.

A common mistake is to "quiet file" the sale year correctly and leave the earlier years untouched. That leaves information-return penalties and open assessment periods in place. It can also undermine a later streamlined certification, because filing the current year selectively suggests you knew about the obligation.

What should you give the buyer?

The aim is to keep the deal on timetable without over-disclosing your personal tax affairs. Typically that means:

• A correctly completed W-9 once you have an SSN, or a short explanation that one is being obtained, if a US counterparty needs it for information reporting.
• Accurate FATCA self-certification to the bank receiving proceeds. A false W-8BEN or self-certification is a serious problem in its own right.
• A confirmation that the matter is personal. A short letter from your preparer confirming you have engaged a firm to bring your personal US filings up to date. This is not a tax opinion on the company.
• Factual answers to company-level diligence questions: whether the company has US operations, US-source income or any US entity classification election.
• Careful warranty and disclosure wording, agreed with your corporate lawyers, so that a tax warranty is not breached by a personal filing failure that does not affect the company.

Buyers rarely need your US returns themselves. Retentions or escrows for a seller's personal US tax are unusual where the company has no US footprint. Your legal advisers should push back if one is proposed without a clear company-level risk behind it.

Earn-outs, loan notes and rollover equity

Cross-border mismatches cause the most trouble with deferred consideration.

• Earn-outs. The UK may tax the value of the right to future consideration at completion under Marren v Ingles principles. The US may use the installment method or wait until payments are received. Foreign tax credits can then fall in a different year from the US tax they are meant to offset. Carryback and carryforward rules help, but the computations need care.
• Loan notes. Qualifying corporate bonds and non-QCBs have specific UK outcomes. The US looks separately at whether the installment method applies and at interest accruals.
• Rollover into buyer shares. A share-for-share exchange that defers UK CGT does not automatically defer US tax. Unless the exchange qualifies as a reorganisation under US rules, the rolled portion can be taxable in the US now. That creates a gain with no matching UK tax to credit against it.

Why the sale changes the citizenship conversation

Many accidental Americans eventually consider giving up US citizenship. That is a personal decision and outside the scope of return preparation. The compliance consequences of timing are worth knowing, though. Under the US expatriation rules, someone is a "covered expatriate", and potentially subject to an exit tax, if they meet a net-worth test of $2 million, an average-income-tax-liability test, or fail to certify five years of US tax compliance on Form 8854. A large exit can take net worth over $2 million overnight. The IRS's separate relief procedures for certain former citizens are also limited to people below that net-worth figure. A completed, accurate compliance history is the starting point either way.

What does this mean in numbers?

Take a simplified illustration. A UK-resident founder who is a US citizen sells 100% of a trading company in 2026/27 for a gain of £5 million, with no Section 1248 or currency complications. In the UK, £1 million is taxed at 18% under BADR and £4 million at 24%, giving UK CGT of £1.14 million, an effective rate of about 22.8%. In the US, the same gain converted to dollars is taxed at 20%. Because the overall UK rate exceeds the US rate, the foreign tax credit generally eliminates the US capital gains tax. The remaining question is the 3.8% NIIT, worth around £190,000 at these figures before any treaty position. Real transactions are rarely this clean. CFC earnings, currency movements and deferred consideration all shift the figures, which is why the returns must be prepared from the actual completion statement.

How we help

We prepare the full streamlined package, the sale-year US return with foreign tax credit and NIIT computations, the Forms 5471 for the company, and the UK Self Assessment and BADR claim, with US and UK figures reconciled to each other. We work alongside your corporate lawyers and the buyer's advisers on the factual confirmations they need. Our IRS streamlined filing team handles the catch-up. Our US-UK tax accountants prepare the sale-year returns in both countries, and our high-net-worth practice deals with the wider reporting that a significant exit brings.

If your US citizenship has come up in a buyer's diligence, a W-9 request or completion KYC, the earlier the compliance work starts, the less it affects your timetable. Contact our cross-border team for a confidential consultation. We will tell you which filings you need, how long they will take, and what you can safely give the buyer this week.