Introduction: Growth Shares UK and the American Shareholder
A growth shares UK award is the most elegant equity instrument in British private company practice, and it is quietly one of the most dangerous things an American can accept. Furthermore, the danger is invisible from the UK side, because the UK analysis genuinely works. Your solicitor is not wrong. However, your solicitor is only solving half of your problem.
At TaxYork we act for American founders, chief technology officers and commercial directors holding equity in British companies. Additionally, we have unwound more failed growth shares UK positions than any other cross-border issue in our practice. Consequently, this guide sets out precisely how a growth shares UK arrangement behaves under both tax systems, and where the two collide.
What Growth Shares UK Arrangements Actually Are
A growth shares UK plan creates a separate share class that participates only in value above a stated threshold, known as the hurdle. Specifically, if the company is worth £10 million today, the hurdle sits at £10 million, and the new class captures nothing below that figure. Therefore, the shares carry very little value on the day they are issued.
That low initial value is the entire point. Moreover, it lets the recipient buy the shares outright for a modest sum rather than receive them free. Accordingly, no employment income arises in the UK, and all future growth falls into the capital gains regime instead.
Why the US Side Breaks the UK Logic
American recipients inherit a second tax system that never heard of hurdles. Specifically, section 83 of the Internal Revenue Code taxes property transferred in connection with services, measured at its own fair market value under its own rules. Consequently, the elegant UK outcome survives only if you take deliberate action within thirty days.
Miss that window and the position deteriorates badly. Furthermore, the damage compounds silently for years before anyone notices. Therefore, the time to read this guide is before the share certificate is signed, not after an exit.
How the UK Taxes Growth Shares
The growth shares UK treatment rests on the employment-related securities rules in Part 7 of the Income Tax (Earnings and Pensions) Act 2003. Understanding it properly matters, because the US analysis borrows several of its facts.
The Hurdle and the Acquisition Charge
When you acquire shares by reason of employment, the UK charges income tax on the difference between unrestricted market value and what you paid. However, a properly hurdled growth shares UK award carries a genuinely small unrestricted value. Therefore, paying that value in cash extinguishes the charge entirely.
Valuation drives everything here. Additionally, HMRC scrutinises hurdle valuations closely, and its Employment Related Securities Manual guidance on valuation issues sets out the expected approach. Consequently, an independent valuation is not optional in practice.
The Section 431 Election and Its 14-Day Deadline
Growth shares UK awards almost always carry restrictions, such as forfeiture on leaving. Those restrictions depress the value, which sounds helpful. However, the restricted securities rules then tax the growth as employment income later, when the restrictions lift.
A joint election under section 431 of ITEPA 2003 solves this by taxing you on unrestricted value immediately. Critically, HMRC guidance on elections to exclude outstanding restrictions confirms the election must be made within fourteen days of acquisition. Furthermore, it must be signed jointly by you and your employer, so it cannot be filed alone.
Capital Gains Treatment and Business Asset Disposal Relief
With the election in place, all subsequent growth becomes capital. Higher and additional rate taxpayers face capital gains tax at 24% under the current gov.uk capital gains tax rates. Additionally, Business Asset Disposal Relief may reduce the rate on the first £1 million of qualifying lifetime gains.
That relief became less generous in 2026. Specifically, HMRC guidance on Business Asset Disposal Relief rates confirms the rate rose to 18% for disposals on or after 6 April 2026, up from 14%. Nevertheless, an eighteen per cent charge still beats twenty-four.
How the United States Taxes the Same Award
Here the picture changes completely. Moreover, nothing your UK adviser filed has any effect on the American analysis.
Section 83 Treats Growth Shares as Property
Shares are property. Therefore, section 83 applies to a growth shares UK award exactly as it applies to restricted stock in a Delaware corporation. Specifically, you recognise ordinary compensation income equal to fair market value less the amount you paid.
Timing depends on vesting. Absent an election, that measurement happens when the substantial risk of forfeiture lapses, not at grant. Consequently, a growth shares UK award that appreciates during a four-year vesting period generates enormous ordinary income along the way.
The Section 83(b) Election and Form 15620
An election under section 83(b) pulls the measurement date back to grant. Furthermore, since the shares are worth very little at that point, the income recognised is trivial. Thereafter, every pound of appreciation is capital.
The IRS now publishes Form 15620 for section 83(b) elections, which standardises what was previously a free-form letter. Use of the form remains voluntary, and the IRS update to Publication 525 confirms a compliant written statement still works. However, the thirty-day deadline is statutory and absolutely unforgiving.
Why US Valuation Rarely Matches the UK Hurdle
British valuers price growth shares UK awards using option methodologies that produce very low figures. American practice, by contrast, applies stricter standards derived from section 409A valuation discipline. Consequently, the US fair market value frequently exceeds the UK unrestricted market value on the same shares.
That gap creates real income. Specifically, where the US figure exceeds what you paid, ordinary income arises even though the UK charged nothing at all. Therefore, commission a valuation that satisfies both jurisdictions rather than one that satisfies neither.
Two Elections, Two Deadlines, One Award
This section contains the single most valuable paragraph in this guide. Furthermore, it is the point that almost every British corporate lawyer misses when a US person joins the cap table.
Fourteen Days for HMRC, Thirty Days for the IRS
The section 431 election runs for fourteen days from acquisition. The section 83(b) election runs for thirty days. Consequently, an American holding a growth shares UK award faces two separate filings, on two separate clocks, in two separate countries.
Diary both dates on the day of grant. Additionally, remember that the UK election needs your employer's signature, which introduces delay you cannot control. Therefore, treat the fourteen-day deadline as the binding one and prepare both documents together.
What Happens When You File Only One
File the section 431 election alone and your UK position is perfect while your US position collapses. Specifically, the IRS then taxes each vesting tranche at ordinary rates, in years when no UK tax arises at all. Consequently, you generate large American liabilities with no foreign tax credit to absorb them.
File the section 83(b) election alone and the mirror image occurs. In that case HMRC taxes the growth as employment income when restrictions lift, at rates up to 45% plus National Insurance. Meanwhile, the United States has already treated the same value as capital.
The Forfeiture Risk You Cannot Deduct
A section 83(b) election is irrevocable after thirty days. Moreover, if you subsequently forfeit the shares by leaving early, section 83(b) denies any deduction for the tax you paid. Therefore, the election is a genuine bet on staying.
The bet is usually worth taking, because the amounts at grant are small. Nevertheless, quantify it before signing. In our experience the election costs a few thousand dollars and saves six figures, yet the arithmetic deserves checking on every single award.
The Foreign Tax Credit Mismatch Nobody Warns You About
Even where both elections land correctly, a structural problem remains. Furthermore, no competing guide we have read addresses it.
Ordinary Income Now, Capital Gains Tax Later
Without a section 83(b) election, the United States taxes your growth shares UK award during vesting. The United Kingdom, meanwhile, taxes nothing until you sell. Consequently, the two charges fall in different tax years on the same economic gain.
Foreign tax credits do not travel backwards. Specifically, the foreign tax credit rules permit a one-year carryback and a ten-year carryforward, which never bridges a five-year gap in the wrong direction. Therefore, the UK tax paid at exit arrives too late to relieve US tax paid at vesting.
The Uncreditable Net Investment Income Tax
At exit, a further charge applies. Specifically, the net investment income tax adds 3.8% on investment income above the threshold, and no foreign tax credit reduces it. Consequently, even a fully credited position leaves an American paying 3.8% that a British colleague never pays.
On a £2 million gain, that surcharge alone exceeds £75,000. Additionally, it applies regardless of how much UK capital gains tax you have already suffered. Therefore, build it into every exit model from the outset.
Why Carryforward Rarely Rescues the Position
Excess credits sound reassuring. However, they only relieve future foreign-source income in the same basket, and a founder who has just exited frequently has none. Consequently, the credits expire unused after ten years.
Sourcing matters here too. Under section 865 of the Internal Revenue Code, gains on personal property generally follow the residence of the seller, and a US citizen with a genuine foreign tax home can treat the gain as foreign-source where the foreign tax reaches ten per cent. Therefore, a UK-resident founder normally clears that test comfortably, which at least keeps the credit alive.
Founder-Specific Exposures on Growth Shares UK Awards
Founders holding growth shares UK awards face three exposures that ordinary employees escape. Moreover, each one arrives without warning at the worst possible moment.
Section 1202 Does Not Reach a British Company
American founders routinely assume the qualified small business stock exclusion protects them. It does not. Specifically, section 1202 requires stock in a domestic C corporation, and a company incorporated in England and Wales fails that test absolutely.
The 2025 reforms made this more painful. Furthermore, the per-issuer exclusion rose to fifteen million dollars with a tiered holding structure, so the relief your American peers enjoy grew while yours stayed at nothing. Consequently, a growth shares UK award can never deliver the outcome a Delaware grant delivers.
Controlled Foreign Corporation Reporting Above Ten Per Cent
Growth shares UK awards frequently push a founder above the ten per cent ownership threshold. At that point you become a US shareholder of a controlled foreign corporation, assuming US persons control the company. Therefore, Form 5471 obligations begin, alongside annual net CFC tested income inclusions.
Penalties here start at ten thousand dollars per form per year. Additionally, they apply whether or not any tax is due. Consequently, we treat the ten per cent line as the single most important number on any American founder's cap table.
Section 1248 on Exit
Selling shares in a controlled foreign corporation can convert capital gain into dividend income. Specifically, section 1248 recharacterises gain to the extent of accumulated earnings and profits attributable to your holding. Consequently, the character of your exit proceeds may differ sharply from what the UK computation shows.
That recharacterisation is not always bad. Nevertheless, it changes the basket, the rate and the credit position simultaneously. Therefore, model it before signing a share purchase agreement rather than afterwards.
A Worked Case Study: An American Founder at a London Software Company
Consider a client we will call Rowan, a US citizen resident in London and chief technology officer of a British software company. The company is worth £10 million when Rowan receives a five per cent growth shares UK award with a £10 million hurdle. Furthermore, Rowan pays the assessed unrestricted market value of £12,000 in cash.
The Grant
Rowan's solicitor filed a section 431 election within fourteen days, so no UK income tax arose. We filed a section 83(b) election within thirty days, using Form 15620. However, the US valuation put fair market value at £18,000 rather than £12,000.
That difference produced ordinary income of £6,000, or roughly $7,800 at $1.30. Tax at 37% came to about $2,886. Consequently, Rowan paid under three thousand dollars to fix the entire position permanently.
The Exit
Five years later the company sold for £60 million. Value above the hurdle reached £50 million, so Rowan's five per cent delivered £2.5 million. The UK capital gain came to £2,488,000 after deducting the £12,000 cost.
Business Asset Disposal Relief covered the first £1 million at 18%, costing £180,000. The balance of £1,488,000 suffered 24%, costing £357,120. Therefore, total UK capital gains tax reached £537,120.
What the Elections Saved
On the US return, Rowan's basis stood at £18,000, giving a gain of roughly $3,226,600. Long-term capital gains tax at 20% came to $645,320, which the UK tax of approximately $698,256 fully absorbed. Nevertheless, net investment income tax of about $122,611 remained payable, because no credit reduces it.
Now consider the alternative. Without the section 83(b) election, roughly $700,000 of US ordinary income tax would have fallen due across the vesting period, in years when Rowan paid no UK tax whatsoever. Consequently, a $2,886 filing on a growth shares UK award saved close to seven hundred thousand dollars, and the UK credit would otherwise have been stranded entirely.
How TaxYork Can Help
We review growth shares UK documentation before it is signed, which is where the value sits. Furthermore, we prepare both elections in parallel and manage the fourteen and thirty day clocks together. Additionally, we commission valuations that withstand scrutiny from HMRC and the IRS simultaneously.
Where awards were granted years ago without US elections, we quantify the damage and rebuild the filing history. Specifically, we prepare US tax returns for expats with correct basis, and we model exit outcomes through our tax treaty optimisation service. Consequently, clients reach completion knowing their net proceeds precisely.
Founders who have never filed at all need a different route entirely. In those cases we use the IRS Streamlined Filing Compliance Procedures alongside FBAR and FATCA reporting for the accounts holding the proceeds. Meanwhile, HMRC, ICAEW technical guidance and the Chartered Institute of Taxation offer useful background on the UK mechanics.
Conclusion
A growth shares UK award remains an excellent instrument for American founders and executives in Britain. However, it only works when both tax systems are addressed on the day of grant. Furthermore, the two elections that make it work run on incompatible deadlines, and neither is retrievable once missed.
Three actions matter above all others. Diary the fourteen-day and thirty-day deadlines the moment terms are agreed. Additionally, obtain a valuation that satisfies American standards rather than British ones alone. Finally, check whether your holding crosses ten per cent, because that single line changes your entire reporting profile.
Ultimately, the arithmetic strongly favours acting early. A few thousand dollars of tax and professional fees at grant routinely protects hundreds of thousands at exit. Therefore, treat the grant date as the deadline that matters, and never the exit date. Further reading on aicpa-cima.com and Investopedia's explanation of the 83(b) election covers the American mechanics in general terms.
Contact Us
Our specialists review equity documentation, prepare both elections and model exit outcomes across the two systems. To discuss a proposed or existing award, contact us or email hello@taxyork.com. Alternatively, call 020 3488 8606 to speak with a US-UK specialist directly.
We act on growth shares UK awards for founders, executives and investors across London and the wider United Kingdom. Furthermore, we handle both filings together, so nothing falls between the two regimes.
Disclaimer
This article provides general information about growth shares UK arrangements and their US tax consequences. It does not constitute tax advice and you should not rely on it in isolation. Tax legislation changes frequently, and individual circumstances vary considerably. Furthermore, figures cited reflect the 2026/27 UK tax year and the 2026 US tax year, and the case study is illustrative rather than a prediction. Accordingly, please obtain professional advice tailored to your own position before acting. TaxYork accepts no liability for action taken on the basis of this article alone.