US Share Options Tax for UK Employees of US Firms | TaxQube Accountants

UK employees of US companies are increasingly rewarded with share options and restricted stock units as part of their remuneration package. If you are UK tax resident, these awards are subject to UK tax rules, regardless of where the employer is based. Understanding the correct UK tax treatment is essential to remain HMRC compliant and to plan your tax position effectively.

This guide explains how US share options and RSUs awarded to UK employees are taxed in the UK, how platforms such as Carta fit into the reporting process, and when specialist advice from TaxQube Accountants is required handle tax management and provide support.

Who this guide is for

This article is written for UK tax resident employees who receive equity awards from US companies, including:

• UK employees of US tech companies

• UK based staff of US startups and scale-ups

• Employees paid partly in equity rather than cash

• Senior employees with share based incentives

If you are on a UK payroll or complete a UK self assessment tax return and have equity shown on Carta or a similar platform, this guide applies to you.

Common types of US equity awards for UK employees

The UK tax treatment depends on the type of award, not the US label used by the company. This can be really confusing as foreign could mean UK (i.e. if you are based in the US, the UK resident is referred to as “foreign/nonresident alien”). The withholding tax is not always a US withholding tax, depending on how the US/UK treaty is applied. A deep understanding of cross-border tax systems is essential to avoid mistakes with terminology and analysis of UK/US documents with an understanding of native terminology.

Share options

Share options give you the right to buy shares at a fixed price in the future. US plans often refer to ISO or NSO options, but HMRC does not recognise these categories and instead applies UK employment related securities rules.

Restricted Stock Units RSUs

RSUs are a promise to deliver shares once vesting conditions are met. They are common for employees of larger US companies and are taxed differently from options in the UK.

Restricted shares

Restricted shares involve shares issued upfront but subject to forfeiture conditions. These awards can create immediate UK tax exposure without careful planning.

UK tax residence and employment duties

UK tax residence is the starting point for determining the UK tax position.

HMRC considers:

• Whether you are a UK tax resident

• Whether the award is employment-related

• Where your employment duties were performed during the vesting period

For employees who have worked partly outside the UK, this analysis can significantly affect the amount taxed in the UK.

How US share options are taxed in the UK

Grant of options

There is usually no UK tax when share options are granted, even if the grant appears on Carta.

Vesting

Vesting alone does not normally trigger UK tax unless the option is exercised at the same time.

Exercise of options

The main UK tax point is exercise.

The difference between the market value of the shares at exercise and the exercise price is treated as employment income.

This amount is subject to:

• Income tax at your marginal rate

• Employee National Insurance contributions where applicable

Employers may be required to operate PAYE in some circumstances, but this is not always done for overseas employers.

Sale of shares

Once the shares are acquired, any further growth in value is subject to capital gains tax when the shares are sold.

Annual CGT allowances and planning opportunities may apply.

UK tax treatment of RSUs

RSUs are taxed as employment income when the shares are delivered to you, not when they are sold.

The taxable amount is the full market value of the shares at vesting.

This applies even if:

• The shares are not sold

• The company is private and the shares are illiquid

• US tax has already been withheld

This frequently creates cash flow issues for UK employees.

How Carta reporting fits into UK tax compliance

Carta is an equity administration platform, not a tax reporting service.

Common UK misunderstandings include:

• Assuming Carta values are automatically accepted by HMRC

• Believing US withholding settles UK tax

• Not reporting equity income through self-assessment

TaxQube reconciles Carta reports with UK tax rules to ensure correct HMRC reporting.

Double tax relief and US withholding tax

US employers often withhold US federal tax on equity income.

As a UK tax resident employee, you may be able to claim double tax relief under the UK-US double taxation treaty, provided:

• The income is taxable in both countries

• The US tax has been correctly withheld and documented

• Double taxation claims to various types of income. For example, let’s say you have given dividends which were previously locked, the tax treaty would have different rates for different types of income

• Foreign Tax Claims

Incorrect claims are a common trigger for HMRC enquiries.

Legitimate tax planning opportunities

While equity taxation is heavily regulated, there are lawful planning strategies available. In some cases, this could mean thousands of extra tax savings when timing is controlled and planned properly.

Timing of exercise

Exercising options in a lower income year can reduce income tax and National Insurance exposure. Pre-IPO tax planning can deliver significant tax savings if you have cash available to complete the transaction and are able to accept the risk.

Capital gains planning

Using annual exemptions, losses and spousal transfers can reduce capital gains tax on disposal.

International workdays relief

Employees who performed duties outside the UK during the vesting period may be able to reduce the UK taxable portion.

Common mistakes made by UK employees

• Assuming US tax paid removes the UK liability

• Reporting only the sale and not the exercise or vesting

• Using Carta valuations without UK adjustment

• Missing PAYE or National Insurance obligations

These errors often lead to back taxes, interest and penalties.

When to use specialist accountants for employees

You should seek specialist advice if:

• You receive US share options or RSUs – Early IPO tax planning or thinking of exiting your investment position.

• Your employer is not operating UK PAYE on equity income and “net shares” are retained after initial equity via payroll.

• You have worked in multiple countries during vesting

• The equity value is significant

TaxQube Accountants specialise in advising UK employees on US equity awards and international employment tax.

How TaxQube can help

We provide:

• UK tax reporting for US share options and RSUs

• PAYE and National Insurance analysis

• Carta reconciliation and HMRC-compliant valuations

• Double tax relief and treaty claims

• Employment-related securities advisory

• Self-assessment tax return services

• International employment tax planning

• Ongoing tax code management and communication with HMRC

Frequently Asked Questions

Q: Are US share options taxable for UK employees

A: Yes. If you are UK tax resident, US share options are usually taxable as employment income when exercised. Specific tax treatment depends on your unique scenario and the company that you work for.

Q: Do UK employees pay tax when RSUs vest

A: Yes. The market value of RSUs at vesting is taxable as income, even if the shares are not sold.

Q: Does Carta report my tax to HMRC

A: No. Carta administers equity plans but does not handle UK tax reporting. It is ultimately the responsibility of the tax resident to ensure that their taxes are handled correctly.

Q: Is it income tax or capital gains tax

A: Income tax usually applies on exercise or vesting, with capital gains tax applying only to later growth if the correct scenario applies. In some cases, even further growth can be considered as employment income.

Q: When should I speak to an accountant

A: Ideally, before exercising options or when RSUs are due to vest, as early advice can prevent unexpected UK tax bills. TaxQube can also help you keep track of unrealised gains which will help you in deciding how much to sell and when to sell. Of course, we cannot comment on the investment growth and strictly analyse these decisions based on the tax efficiency.

TaxQube can help your business 

We help taxpayers in the UK to ensure compliance with HMRC – It is a legal responsibility. If you need help in submitting your Tax reports or accounts preparation, please do feel free to get in touch with us by completing the contact us form.