Tender Offer Tax: Why a Startup Liquidity Event Is Harder From London
A tender offer is often the first time an early employee of a private technology company turns paper wealth into cash. For an American living in Britain, however, the same sale lands in two tax systems at once, and each system asks a different question about what you actually sold. The IRS wants to know whether the money is compensation or capital gain. HMRC wants to know whether the price exceeded market value, whether your shares became readily convertible assets, and how much of the gain relates to work you did while resident in the UK.
Most of the guidance online is written for employees in California or New York. It explains incentive stock options, the alternative minimum tax and state residency, and then stops. In contrast, a US citizen employed in London by the British subsidiary of an American company faces UK payroll withholding, UK capital gains tax at 24 per cent, US tax on worldwide income, and a foreign tax credit calculation that splits the proceeds across two baskets. Consequently, a tender offer that looks simple in the company's FAQ can produce withholding in both countries on the same dollars.
In our experience preparing returns for founders, engineers and executives at venture-backed companies, the costly errors rarely come from the headline tax rates. Instead, they come from sourcing, from exchange rates, and from payroll mechanics that neither employer anticipated. This guide explains how a tender offer is taxed on both sides of the Atlantic in 2026, where the rules collide, and how to structure your participation so that the second tax bill is credited rather than paid twice.
How a Tender Offer Works for Startup Employees
In a typical tender offer, the company, an existing investor or a new investor offers to buy a fixed number of shares from current and former employees at a set price. The offer stays open for a limited window, usually around 20 business days, which reflects the minimum period the SEC tender offer rules set for offers that fall within them. Employees can usually sell vested shares they already own, and many offers also allow a cashless exercise of vested options so that the option holder receives the net proceeds after paying the strike price.
Because the buyer is often a sophisticated investor paying a negotiated price, the tender price frequently sits well above the company's latest common stock valuation under section 409A. That gap is where the tax analysis begins. Furthermore, the legal form matters: a company buyback, a third-party purchase and a structured secondary through a special purpose vehicle can each carry different tax consequences for the seller.
Who This Guide Is Written For
This guide addresses US citizens and green card holders who live in the UK and hold shares or options in a private company, usually a US-incorporated startup with a British subsidiary. It also applies to Americans who moved to London part-way through their vesting schedule, and to those who exercised options in the United States before relocating. If your tender offer allocation runs to six or seven figures, the sourcing and credit decisions below will change your net proceeds materially.
US Tender Offer Tax: How the IRS Treats Your Proceeds
The US analysis of a tender offer starts with the type of equity you are selling. Shares you already own produce capital gain or loss, measured in dollars from your cost basis. Options you exercise in order to sell produce compensation income on the spread, and the character of that income depends on the option type. The IRS guidance on stock options sets out the default treatment for statutory and non-statutory options.
Shares You Already Own
If you exercised options or received restricted stock years ago, the shares are capital assets in your hands. Selling them in a tender offer produces a capital gain equal to the proceeds minus your basis, which is normally the strike price plus any income you recognised on exercise or vesting. Where you held the shares for more than a year, the gain is long-term. For 2026 the 20 per cent federal rate begins at taxable income above $545,500 for a single filer and $613,700 for a married couple filing jointly, as the IRS explains in its guide to capital gains. Moreover, the 3.8 per cent net investment income tax generally applies on top for high earners.
Options Exercised Into the Offer
Non-qualified options exercised to participate produce ordinary income on the difference between the tender price and the strike price. Your employer treats that spread as wages, reports it on Form W-2 and withholds federal income tax at the supplemental rate of 22 per cent, rising to a mandatory 37 per cent on supplemental wages above $1 million in the year. Because you sell the shares immediately, your basis equals the tender price and there is no further gain.
Incentive stock options work differently. If you exercise and sell in the same tender offer, you make a disqualifying disposition, so the spread becomes ordinary income rather than long-term capital gain. For a resident of California that is usually a loss of tax benefit. For an American in London, as we explain below, it is often the better outcome because it aligns the US timing with the UK charge.
When the Premium Becomes Compensation
The IRS pays close attention where the tender price exceeds the fair market value of common stock. If the buyer is the company, or an investor acting with the company's encouragement, and employees can sell at a price above what an outsider would pay for common shares, part of the proceeds may be compensation rather than sale price. The risk rises where only employees can participate, where the price reflects preferred-stock economics, or where the allocation depends on continued employment. In that case the excess is ordinary income, subject to wage withholding, even though the shares themselves were long held.
Qualified Small Business Stock
Some startup shares qualify for the section 1202 exclusion. Where they do, a tender offer sale after the required holding period can be partly or wholly free of federal tax. However, the UK has no equivalent relief, so a UK resident still pays capital gains tax on the whole gain and has no US tax against which to credit it. Our guide to QSBS for US founders abroad explains why the exclusion is worth far less to a British resident than it appears.
UK Tender Offer Tax: How HMRC Taxes the Same Sale
HMRC approaches a tender offer through the employment-related securities code in the Income Tax (Earnings and Pensions) Act 2003, and only then through capital gains tax. The sequence matters, because any amount taxed as employment income is removed from the capital gain. HMRC's guidance on how employment-related securities work confirms that shares acquired by reason of employment remain within this code for as long as you hold them.
Capital Gains Tax on Shares You Already Own
Where you sell shares at market value, the gain is subject to capital gains tax at 18 per cent within the basic rate band and 24 per cent above it, after the annual exempt amount of £3,000. The current capital gains tax rates apply to shares regardless of whether the company is British or American. Crucially, HMRC measures the gain in sterling, converting your acquisition cost at the exchange rate on the day you acquired the shares and your proceeds at the rate on the day of the tender offer.
Chapter 3D and the More Than Market Value Charge
Chapter 3D of Part 7 of ITEPA 2003 contains the rule most American employees have never heard of. Where employment-related securities are disposed of for more than their market value, the excess is taxed as employment income under section 446Y of ITEPA 2003. The charge equals the consideration received, less market value, less disposal expenses, and it arises in the tax year of the sale.
In a genuinely arm's-length tender offer run by an independent investor, the price usually is market value, so Chapter 3D does not bite. However, where the company buys back its own shares at a premium, or where an investor pays employees a price it would not pay an unconnected seller, HMRC can argue that part of the proceeds is employment income taxed at up to 45 per cent rather than capital gain taxed at 24 per cent. Accordingly, the valuation evidence behind the price is as important in London as it is in the United States.
Readily Convertible Assets and PAYE
A tender offer can also change how HMRC treats options exercised at the same time. Once trading arrangements exist that let you turn shares into cash, the shares become readily convertible assets. Your UK employer must then operate PAYE on the income from an unapproved option exercise or an RSU settlement, and Class 1 National Insurance applies. The HMRC helpsheet HS305 on employment-related shares explains how this income flows through your Self Assessment return.
Where the employer accounts for PAYE but cannot deduct enough from your salary, you must make good the tax within 90 days. Otherwise, section 222 of ITEPA 2003 treats the unpaid tax as a further taxable benefit. In practice, a well-run tender offer deducts UK tax from the gross proceeds before they reach you, but US-headquartered payroll teams do not always know that the UK subsidiary has this obligation.
EMI Options and Tax-Advantaged Schemes
Options granted under the Enterprise Management Incentive scheme or a Company Share Option Plan can be exercised into a tender offer without an income tax charge, provided the exercise complies with the scheme terms. The whole gain then falls under capital gains tax, and EMI shares can qualify for Business Asset Disposal Relief at 18 per cent from 6 April 2026 where the option was granted at least two years before the sale. Nevertheless, the US does not recognise EMI status, so the American holder still has ordinary income on exercise. Our analysis of EMI share options and US tax covers that mismatch in detail.
Where Tender Offer Tax Collides for US-UK Dual Filers
The two systems tax the same sale, but they rarely tax it in the same way. Therefore, the planning work in any tender offer lies in the collisions: which country has first taxing rights, which basket the income falls into, and whether the credit arrives in the same year as the tax.
Sourcing Compensation Across Two Countries
When you exercise options, the US sources the compensation by reference to where you performed the services between grant and vesting. Under the Treasury regulations on sourcing compensation for services, an option granted while you worked in San Francisco and vested after you moved to London is split by workdays. The US-source slice carries no foreign tax credit, because the UK usually does not tax it either.
HMRC applies a comparable apportionment for internationally mobile employees, taxing the proportion of the gain that relates to UK duties across the same relevant period. As a result, the two countries usually agree on the split, but only if both returns use the same workday records. Where the US return treats the whole spread as foreign-source and the UK return taxes only 80 per cent of it, the IRS will eventually disallow credits that were never supported.
The Treaty and Your Capital Gain
Under the US-UK income tax treaty, gains on shares are taxable in the country of residence. The saving clause lets the US continue to tax its own citizens, but Article 24 then requires the US to give credit for the UK tax, treating the gain as arising in the UK to the extent necessary to avoid double taxation. Separately, section 865 of the Internal Revenue Code treats a gain as foreign-source for a citizen with a foreign tax home only where at least 10 per cent foreign tax is paid on it, and UK capital gains tax at 24 per cent comfortably clears that bar.
Two Baskets, Two Credit Limits
The foreign tax credit is calculated separately for each category of income on Form 1116. The option spread from a tender offer is general category income, while the gain on long-held shares normally falls in the passive category. UK income tax at 45 per cent on the spread will usually exceed the US tax on it, creating general-basket carryforwards. Meanwhile, UK capital gains tax at 24 per cent exceeds the 20 per cent US rate, creating passive-basket excess credits. Neither excess can be used against the other basket, and they expire after ten years.
National Insurance is a further trap. Employee Class 1 contributions are social security, not income tax, and they are not creditable against US tax. Similarly, the IRS position, upheld by the Tax Court, is that the net investment income tax is not reduced by UK tax under the treaty, so the 3.8 per cent surcharge on the capital gain usually remains payable even when UK tax exceeds the US bill.
Exchange Rates Can Create a Gain in Only One Country
Because the UK computes the gain in sterling and the US in dollars, a tender offer can produce very different figures in each country. If the pound weakened between your purchase and the sale, the sterling gain exceeds the dollar gain, and the UK taxes currency movement the US never recognises. If the pound strengthened, the reverse happens. Our guide to which exchange rate to use on US and UK returns explains how to document both conversions.
Incentive Stock Options Held Across the Move
Britain treats a US incentive stock option as an unapproved option, taxing the spread as employment income when you exercise. The US, by contrast, taxes nothing on exercise for regular tax purposes but may charge alternative minimum tax. If you exercise early and sell later in a tender offer, the UK tax falls in the exercise year while the US tax falls in the sale year, and the credit may not line up. Consequently, a same-day exercise and sale, which creates a disqualifying disposition, is frequently the cleaner result for an American in London. Our article on the expat alternative minimum tax trap shows how the AMT foreign tax credit works when the timing does not match.
Withholding, Reporting and Cash Flow
The tax is only half of the problem. Equally important is who withholds what, and when you get excess withholding back.
US Payroll Withholding You Do Not Owe
When a US parent runs the tender offer through its own payroll, it often withholds federal income tax on the full option spread, even though most of it is foreign-source income that UK tax will cover. That over-withholding is refundable, but only when you file your US return, which for an American abroad can be as late as October of the following year. In the meantime, UK PAYE has also been deducted, so a large share of your proceeds can sit with two treasuries for more than a year.
Coordination before the offer closes is therefore worth real money. Where you expect to claim the foreign earned income exclusion instead, Form 673 lets you ask the employer to stop withholding on excludable wages, although for high earners the exclusion of $132,900 for 2026 rarely beats the credit. In most cases, the better route is agreeing the sourcing with payroll in advance and documenting the UK withholding.
Social Security on the Spread
The option spread is also wages for social security purposes. Under the US-UK totalisation agreement, an employee usually pays into only one system, and a certificate of coverage determines which, as the IRS summary of totalization agreements explains. If you are on UK payroll, UK National Insurance normally applies and US FICA should not be withheld. Where both have been deducted, the US contributions can be reclaimed from the employer or the IRS, but only with the right paperwork.
UK Self Assessment and Payments on Account
A tender offer gain must appear on your UK Self Assessment return for the tax year of the sale, due by 31 January following the end of that year. If you do not already file, you must register by 5 October after the tax year ends, using HMRC's Self Assessment registration service. A one-off gain will also inflate your payments on account for the next year, so it is usually right to apply to reduce them once the sale is behind you.
FBAR and Form 8938 After the Money Lands
When tender proceeds arrive in a UK bank or brokerage account, the balance will almost certainly push you over the $10,000 aggregate threshold for the FinCEN foreign bank account report. Likewise, Form 8938 applies once foreign financial assets exceed $200,000 at year end, or $300,000 at any time, for a single filer living abroad. A missed FBAR on a seven-figure balance is precisely the kind of reporting failure that turns a planned liquidity event into a compliance problem. Our FBAR and FATCA reporting service makes sure the accounts that receive your proceeds are reported correctly.
US Estimated Tax
Tender proceeds rarely have enough US withholding on the capital gain element, because shares you already own are not wages. Unless you meet the prior-year safe harbour, which for adjusted gross income above $150,000 requires paying 110 per cent of last year's tax, an underpayment penalty will run from the quarterly due date. The IRS guidance on estimated taxes explains the deadlines, and our specialists model the payment before the offer settles.
Tender Offer Case Study: A US Engineer in London Sells $1.16 Million
The following illustration uses realistic figures. Daniel is a US citizen and a senior engineering director at a US-incorporated artificial intelligence company. He worked in San Francisco until January 2022 and has since been employed in London by the company's UK subsidiary, where he is an additional-rate taxpayer. In June 2026 a growth investor launches a tender offer at $30 per share for common stock, and Daniel participates with two blocks of equity.
Block One: Shares He Already Owns
In 2021, while still in California, Daniel exercised options over 20,000 shares when their fair market value was $5, so his US basis is $100,000. He sells all 20,000 shares for $600,000, producing a long-term capital gain of $500,000. For the US, federal tax at 20 per cent is $100,000, and the net investment income tax adds $19,000.
For the UK, his acquisition cost converts at the 2021 rate of $1.38 to the pound, giving £72,464. His proceeds convert at $1.35, giving £444,444. After the £3,000 annual exempt amount, the taxable gain is £368,980, and capital gains tax at 24 per cent is £88,555, or roughly $119,550. Because the gain is re-sourced to the UK, that UK tax fully offsets the $100,000 of regular US tax in the passive basket, leaving about $19,550 of excess credit to carry forward. However, the $19,000 net investment income tax remains payable.
Block Two: Options Exercised Into the Offer
Daniel also holds 20,000 vested non-qualified options with a strike price of $2. He exercises them cashlessly in the tender offer, so the spread is $28 per share, or $560,000. The options were granted in 2021 and vested over four years, and his workday records show 20 per cent of the vesting period was worked in the United States and 80 per cent in the UK.
HMRC taxes the UK portion of $448,000, or £331,852, as employment income through PAYE. Income tax at 45 per cent is £149,333, roughly $201,600, and employee National Insurance at 2 per cent adds £6,637, while the UK subsidiary bears employer contributions. For the US, the whole $560,000 is ordinary income. At a 37 per cent marginal rate, US tax on the foreign-source $448,000 is $165,760, which the UK income tax fully covers, leaving about $35,840 of general-basket excess credit. The US-source $112,000 has no foreign tax against it, so US tax of $41,440 is due.
What Planning Changes
Without coordination, the US parent's payroll withheld 22 per cent of the full spread, or $123,200, at the same time as UK PAYE was deducted. Daniel would have waited until his 2026 US return to recover more than $80,000 of that withholding. Instead, with sourcing agreed in advance, the withholding tracks the US-source slice and his estimated payments cover the net investment income tax.
Taken together, Daniel's UK tax is about £244,525, or $330,100, and his net US tax is $41,440 plus $19,000, or $60,440. The combined bill of roughly $390,500 on $1,060,000 of income and gain works out at about 37 per cent. More importantly, it is paid once, with $55,390 of excess credits preserved for future years, rather than twice with a refund claim pending. Furthermore, because the proceeds landed in his London account, Daniel's FBAR and Form 8938 for 2026 must include that account at its highest balance.
Planning Before You Accept a Tender Offer
Lot Identification, Workdays and Valuation
The decisions that matter most are made before the tender offer closes, not when you file. First, identify each lot of equity you plan to sell, its acquisition date, its dollar basis and its sterling basis, because the UK share identification rules will pool identical shares even where the US lets you choose specific lots. Where you hold shares bought at different prices, a partial sale can produce different gains in each country.
Second, gather your workday history for every option and RSU grant. The sourcing split drives both the UK charge and the US credit, and an employer's global mobility team will often ask for it before it calculates withholding. Third, ask the company how it will treat the price for tax purposes, including whether a valuation supports the premium over the 409A figure. If there is a real Chapter 3D or compensation risk, you want to know before you sign the election form.
Exercise Order and Cash Planning
Fourth, consider the order of exercise. Where you hold incentive stock options, a same-day exercise and sale usually aligns US and UK income. Where you hold EMI options, the UK outcome is favourable, but the US will still tax the spread as ordinary income. Finally, plan the cash: set aside funds for UK Self Assessment, US estimated tax and any payment on account before you spend or reinvest the proceeds. Our team, which provides US tax returns for expats alongside UK filings, can run these numbers on both sides before the deadline.
When Earlier Years Need Attention
A tender offer often exposes gaps in prior filings. Employees who exercised options before moving to London, received RSUs through a US broker, or never reported the UK accounts holding their salary may find that the documents requested for the sale reveal missed US tax returns or missed FBARs. Where that happens, it is far better to correct the position before the proceeds arrive than after HMRC or the IRS starts asking. Our treaty and double tax relief work regularly includes rebuilding prior-year credits so that past UK tax is not wasted.
How TaxYork Can Help
TaxYork prepares combined US and UK returns for Americans in Britain who hold private company equity. Because we handle both returns, the sourcing, credits and exchange rates in each one reconcile rather than contradict each other.
Before a tender offer closes, we model the sale in both currencies, identify which lots to sell, and calculate the UK PAYE and US withholding each block should attract. Subsequently, we work with your employer's payroll or mobility team so that withholding matches the actual liability. Our related guides on employment related securities and cross-border RSU tax explain the wider share-scheme rules.
After the sale, we prepare Form 1040, Form 1116 for each basket, Form 8949, the FBAR and Form 8938 alongside your UK Self Assessment return and capital gains pages. Where earlier years contain errors, we correct them in the same engagement, so your liquidity event starts from a clean record.
Conclusion
A tender offer is a welcome chance to convert startup equity into cash, but for an American in London it is taxed twice by design. The IRS asks whether the proceeds are compensation or gain, while HMRC asks whether the price was market value, whether PAYE applied, and how much relates to UK duties. The rates themselves are manageable. The real costs come from unsupported sourcing, double withholding, uncreditable National Insurance and the net investment income tax, and from exchange rates that create a gain in only one country.
Handled properly, however, the UK tax on both the spread and the gain can usually be credited against the US bill, leaving only the US-source slice and the surcharge to pay. The work has to start before the offer closes, with lot identification, workday records and a withholding plan agreed with your employer. With that preparation, your tender offer is taxed once, fully reported, and free of surprises when the returns are filed.
Contact Us
If you have been invited to participate in a tender offer while living in the UK, or you have already sold shares in a secondary and are unsure how to report it, speak to us before the filing deadlines. We will quantify your position in both countries and show you exactly where planning still helps.
Email hello@taxyork.com or call 020 3488 8606 to speak with a cross-border specialist. Alternatively, book a consultation and we will review your equity and your filing history confidentially.
Disclaimer
This article provides general information about the US and UK taxation of tender offers and secondary share sales for US citizens and green card holders resident in the United Kingdom. It does not constitute tax, legal or financial advice, and you should not rely on it for any specific transaction. The case study is illustrative, uses assumed exchange rates and simplified marginal rates, and your outcome will depend on your equity terms, residence history and employer arrangements. Accordingly, you should obtain professional advice tailored to your circumstances before acting. TaxYork accepts no liability for any loss arising from reliance on this material.