US UK Tax returns preparation: Double-Trigger RSUs Guide

Double-trigger RSUs in a private US company are taxed by neither country while the liquidity condition is outstanding. When it is met, the US taxes a citizen on the full value and the UK taxes the share earned through UK service, so accurate US UK Tax returns preparation turns on sourcing and credit, not the headline figure.

At Jungle Tax we prepare both the US and the UK return for senior executives whose awards sat dormant for years and then became taxable in a single afternoon, often in a country they were not living in when the award was granted. Most published material on double-trigger RSUs is written for an employee who never leaves the United States. It explains the two conditions and the withholding shortfall and stops there. This guide starts where those pages end: what happens when the first trigger was satisfied in one country and the second fires in another.

It is a companion to our general guide to RSUs and stock options for dual filers, and to the separate pieces on trailing vesting after leaving the UK and startup tender offers. Those cover listed-company vesting schedules and secondary sales. Nothing here repeats them.

What is a double-trigger RSU, and why is nothing taxed before the second trigger?

A double-trigger restricted stock unit is a promise to deliver shares once two conditions have both been met. The first is a service condition: typically four years of continued employment, satisfied in tranches. The second is a liquidity condition: an initial public offering, a sale of the company, or another defined event. An award that has met the first condition but not the second is commonly described as time-vested. It is not vested in any sense that matters to either tax authority.

The US position

For US federal income tax, an RSU is an unfunded promise, not property. Section 83 of the Internal Revenue Code taxes property transferred in connection with services, and no property is transferred until shares are delivered. The income is therefore recognised as wages at settlement, measured by the fair market value of the shares on that date. IRS Publication 525 sets out the general treatment of restricted stock units as compensation.

The second trigger is there largely because of Section 409A. Deferred compensation that fails Section 409A is taxed early and carries an additional 20% tax. The regulations exclude a short-term deferral: an amount paid no later than the 15th day of the third month following the end of the year in which it ceases to be subject to a substantial risk of forfeiture. Under those regulations a substantial risk of forfeiture can rest on a condition related to a purpose of the compensation, and a genuine liquidity condition is drafted to be exactly that. While it remains outstanding, the award is still forfeitable, nothing is deferred, and nothing is taxed.

The UK position

HMRC reaches the same result by a different route. Since 6 April 2016, an RSU that gives the holder a right to acquire shares has been treated as a securities option and taxed under Chapter 5 of Part 7 of ITEPA 2003. There is no charge on the grant of a securities option. The charge arises when shares are acquired under it, on their market value at that date less anything paid. An award that can only be settled in cash is outside these rules and is taxed as earnings when paid.

So at the point most executives relocate, with tranches time-vested and no exit in sight, there is nothing to report on either return. That silence is the source of the difficulty. Years pass, residence changes, payroll records are archived, and then the whole award becomes income on one date.

When does each country treat the award as earned?

Being taxable and being earned are separate questions. The first fixes the year and the amount. The second decides which country the income belongs to, and for a mobile executive it is the more consequential of the two.

United States. Treasury Regulation 1.861-4 sources multi-year compensation on a time basis over the period to which it is attributable, determined on the facts and circumstances. For stock options the regulation says that period is generally from grant until all employment-related conditions have been satisfied. Applied to an RSU, that points to the service period.

United Kingdom. Chapter 5B of Part 2 of ITEPA 2003 apportions securities income over a statutory relevant period. For a securities option, HMRC's manual at ERSM162565 explains that the period begins on the day the option is acquired and ends on the day of the chargeable event or, if earlier, the day the option vests. Income is treated as accruing evenly over each day of that period. Section 41G also allows a different period to be used where the statutory one would not produce a just and reasonable result.

Does the earning period end at the time-vesting date or at the liquidity event?

This is the question on which a double-trigger award turns, and neither country answers it with a fixed rule. It depends on what the award agreement requires between the two dates.

• Service required to the liquidity event. If the holder must still be employed when the second trigger occurs, every day up to that event is a day on which the award was being earned. Both systems should then measure from grant to the liquidity event.
• No further service required. If a time-vested tranche survives a resignation and simply waits for an exit, the services that earned it ended on the time-vesting date. The US facts-and-circumstances test supports measuring to that date. HMRC's own example of an option that requires three years of employment and then becomes exercisable later, or on an exit, treats the relevant period as the three years of the employment condition.
• Tranches are measured separately. Each tranche of a graded schedule has its own period. A first tranche that time-vested before a move can sit wholly on one side of the border while the last tranche straddles it.

Where the statutory period is displaced in favour of a just and reasonable one, the basis should be documented and applied consistently on both returns. The damage is rarely done by choosing the wrong period. It is done by using one period on the US return and another on the UK return.

US versus UK treatment of a double-trigger RSU at a glance

How is the income sourced when the trigger fires years after the move?

Take an illustration. An executive, a US citizen, is granted a single tranche on 1 January 2021 that time-vests after four years. She works in the US until 31 December 2022, moves to London on 1 January 2023 and remains with the same group. The company lists on 1 March 2027 and the shares, worth $2,000,000, are delivered that month.

If no service was required after the time-vesting date, the earning period is the 48 months to 31 December 2024. Twenty-four were worked in the US and 24 in the UK. Half the income, $1,000,000, is attributable to UK service.

If she had to remain employed until the listing, the period is the 74 months from January 2021 to February 2027. Fifty of those were UK months, so roughly 67.6%, about $1,350,000, is attributable to UK service.

The US taxes the full $2,000,000 on the 2027 Form 1040 in either case, because she is a citizen. What changes is the foreign-source fraction on Form 1116, and therefore how much UK tax can be credited. On the UK side, the months before arrival were worked abroad as a non-resident, so the part of the income accruing in that period is not chargeable. The rest falls into the 2026-27 UK tax year. A difference of some $350,000 between the two answers is the difference between a credit that covers the UK tax and one that does not.

Arriving in the UK

Once UK resident, an executive is taxable on securities income accruing during UK residence whether the duties were performed in London or on business trips abroad. Workdays outside the UK reduce the UK charge only where a relief is properly claimed. For those who became UK resident on or after 6 April 2025 and qualify under the four-year foreign income and gains rules, overseas workday relief can apply to securities income for the qualifying years, subject to an annual limit. Remittance basis rules continue to govern the part of any relevant period that falls before that date. Each has to be claimed on the return; none is automatic.

Leaving the UK

The reverse case catches more people. An American who time-vested in London, returned to the US, and receives shares years later remains within the UK charge on the portion of the award attributable to UK service, despite being non-resident on the trigger date. Article 14 of the US-UK income tax treaty preserves the UK's right to tax employment income to the extent the employment was exercised in the UK. The US taxes the whole amount and gives credit for the UK tax on the UK-source part.

Who withholds when the employer has no UK presence?

A private US company with an executive working from London and no UK subsidiary, branch or payroll is a common arrangement, and it produces the most uneven withholding position of all.

PAYE. The obligation to operate PAYE rests on an employer with a UK presence. Where the employee of an overseas employer works for a UK business, section 689 of ITEPA 2003 treats that business as the employer for PAYE purposes. Where there is no UK presence and no such business, nobody is required to deduct, and the income is self-assessed. Shares that can be sold on a market at the liquidity event are readily convertible assets, so where a PAYE obligation does exist it applies to the value of the shares, and tax the employee fails to make good to the employer within 90 days of the end of the tax year can itself become a further taxable benefit.

National Insurance. Coverage is allocated by the US-UK social security agreement, generally to the country where the work is done, unless a certificate of coverage keeps a temporary assignee in the home system. An executive covered in the UK owes employee contributions, at 2% on earnings above the upper earnings limit, even where the employer has no UK place of business and the contributions must be paid by direct arrangement with HMRC. The same executive should not also suffer US Social Security and Medicare deductions on the same pay.

US withholding. The US employer will report the full value on Form W-2 and, in most cases, withhold federal income tax at the supplemental rate: 22% up to $1 million of supplemental wages in the year and 37% above it. There are statutory exceptions from wage withholding for certain citizens working abroad, but payroll teams seldom apply them to a one-off equity settlement.

The outcome is that US tax is withheld on all of the income, including the part on which the UK has the first claim, and UK tax is withheld on none of it. The UK liability then falls due on 31 January after the end of the tax year. Because so little was deducted at source, the self-assessed bill will normally also set payments on account for the following year, each equal to half of it, unless a claim to reduce them is made.

What goes on each return in the trigger year?

The US return

• The full value of the shares at settlement as wages on Form 1040, agreeing to Form W-2.
• A sourcing schedule dividing those wages between US and foreign workdays over the earning period, tranche by tranche.
• Form 1116 in the general category for UK income tax on the foreign-source portion.
• Where UK tax falls on income the US regards as US-source, a second Form 1116 for income re-sourced by treaty, with Form 8833 disclosing the treaty position.
• Form 8949 for any shares sold or withheld to cover tax, with basis equal to the value already taxed as wages. Broker statements frequently report that basis as nil.
• A nonresident or part-year return for any US state in which part of the award was earned. Several states apportion equity income by workdays in the state and pursue former residents for it.

The UK return

• The UK-chargeable portion as employment income, converted to sterling at the rate on the acquisition date. Where no PAYE was operated, share-related income is entered on the additional information pages (SA101).
• The residence pages (SA109) where the year is a split year or a treaty claim is made.
• The foreign pages (SA106) for any claim to credit US tax.
• A capital gains computation for shares sold in the year, with the amount charged to income tax forming the base cost, subject to the UK share identification rules.

How is the foreign tax credit claimed?

The order matters. On the portion attributable to UK service, the UK has the first right to tax and the US gives credit. On the portion attributable to US service, the US has the first right. If the UK also taxes that portion, because the executive was UK resident while performing the US duties, the UK credits the US tax, but for a US citizen only up to the amount the US could have charged a UK resident who was not a citizen. Any double tax that remains is relieved on the US return through the re-sourcing rule in Article 24 of the treaty.

Three practical points follow.

• Withholding is not tax. HMRC gives credit for US tax finally due under the treaty, not for the amount withheld. US withholding on the UK-source portion is recovered as a refund on Form 1040, never as a credit against UK tax.
• The years do not align. A trigger in March 2027 falls in US year 2027 but UK year 2026-27, with the UK tax payable in January 2028. Whether credit is claimed on a paid or accrued basis decides which US return it lands on; see our guide to the paid and accrued bases. Unused credit can be carried back one year and forward ten.
• The exclusion is rarely available. Earned income is attributed to the year the services were performed, and pay received after the end of the year following that year is not foreign earned income for Section 911 purposes. A trigger that fires three years after the work was done leaves the credit as the only relief.

What gets missed on double-trigger RSUs?

• The UK return is never filed. With no PAYE and a W-2 showing US tax withheld, the executive assumes the matter is settled. It is the single most common omission we see.
• The UK charge on a former resident. Awards time-vested during a London posting are overlooked when the trigger fires after a return to the US.
• Two different earning periods. One return measures to the time-vesting date, the other to the liquidity event.
• Credit claimed for withholding. US withholding is entered as a UK credit, HMRC later denies it, and the US refund period has moved on.
• Social security in both countries, or neither.
• State returns. A former state of residence taxes its workday share and no return is filed.
• Basis on shares withheld or sold to cover tax, reported as a second gain on the same income.
• An early trigger. If the company waives the liquidity condition, for example to let holders take part in a share sale, the award becomes taxable in that year, not at the eventual exit.
• Relief not claimed. Overseas workday relief or treaty apportionment was available and the full amount was taxed.

How are prior years corrected?

United States. An incorrect return is corrected on Form 1040-X. The ordinary refund period is three years from filing, but a claim that depends on foreign tax credits can be made within ten years of the due date of the return for the year concerned, which matters when UK tax is paid late on a disclosure. Where US returns were not filed at all, or the award sits among other unreported foreign accounts, the Streamlined Filing Compliance Procedures allow a non-wilful taxpayer living abroad to submit three years of returns and six years of FBARs without the offshore penalty.

United Kingdom. A Self Assessment return can be amended within 12 months of the filing deadline. After that, tax overpaid is reclaimed by an overpayment relief claim within four years of the end of the tax year, and tax underpaid is put right by an unprompted disclosure to HMRC. HMRC's own assessing period is four years, six where the error was careless and 20 where it was deliberate, with a 12-year period for offshore matters. A claim to credit foreign tax must be made within four years of the end of the tax year or, if later, by 31 January after the year in which the foreign tax was paid. If the US tax credited is later reduced, HMRC must be told.

The corrections have to be sequenced. The UK liability is settled first, on the correct fraction; the US return is then amended to claim credit for the tax actually paid. Done the other way round, the US claim rests on a figure that has not yet been assessed.

Records to assemble before, or after, the second trigger

• The award agreement and plan rules, in particular what happens to a time-vested tranche on leaving and the exact definition of the liquidity event.
• The grant date and time-vesting date of every tranche.
• A workday calendar by country for the whole earning period, supported by travel records.
• Dates of UK arrival and departure and the residence position for each UK tax year.
• Any certificate of coverage under the social security agreement.
• The settlement statement: shares delivered, shares withheld, value per share and the tax remitted to each authority.

These are much easier to obtain while the company still has its pre-listing payroll and equity administration in place than three years after an acquisition has dissolved both. Our US and UK accountants prepare both returns from one sourcing schedule, so that the fraction, the exchange rate and the credit agree across the two filings. Further cross-border equity topics are indexed in our guides library.

Speak to us before, or after, the second trigger

A double-trigger award concentrates years of earnings into one filing season in two countries, with withholding that seldom matches either liability. Whether your liquidity event is approaching or has already passed without a UK return, a US credit or a state filing, the position can be put in order. To arrange a confidential consultation on your US and UK returns for the trigger year, or on correcting earlier ones, contact our cross-border team.