Introduction
The long-term resident inheritance tax regime now decides whether a wealthy American in Britain faces 40% UK inheritance tax on their worldwide estate. Since 6 April 2025, the United Kingdom has abolished domicile as the trigger for inheritance tax and replaced it with a residence-based test. Consequently, the old planning that many affluent US families relied upon has vanished overnight. Furthermore, the change affects far more than a UK flat or a portfolio held in London. Instead, it can reach a Manhattan apartment, a Delaware LLC, a family trust, and even inherited wealth sitting quietly in a US brokerage account.
Americans abroad already juggle two tax systems that rarely align. Therefore, the arrival of the long-term resident test creates a fresh layer of complexity precisely where the stakes sit highest — estate value. Moreover, the interaction between UK inheritance tax and the US federal estate tax can produce double taxation if you plan carelessly. In this comprehensive guide, we explain exactly how the new rules work, who they capture, and what strategic steps sophisticated clients should take now. Additionally, we illustrate the mechanics with a detailed case study drawn from the kind of high-net-worth scenarios our specialists handle every week.
Understanding the Long-Term Resident Inheritance Tax Test
Why the Long-Term Resident Inheritance Tax Rule Replaced Domicile
The long-term resident inheritance tax test represents the most significant estate reform in a generation. Historically, the UK levied inheritance tax on worldwide assets only once an individual became UK domiciled or deemed domiciled. Domicile, however, proved slippery, subjective, and endlessly litigated. Consequently, the Government scrapped it entirely for inheritance tax purposes and adopted a clean, mechanical residence test instead.
Under the new system, you become a long-term resident once you have been UK resident for at least ten of the previous twenty tax years. Thereafter, your entire worldwide estate falls within the scope of UK inheritance tax. Notably, this is a purely arithmetic test based on the Statutory Residence Test, so there is far less room for argument than domicile ever allowed. The reform was set out clearly by HM Treasury and HMRC.
https://www.gov.uk/government/publications/reforming-the-taxation-of-non-uk-domiciled-individuals
https://www.gov.uk/government/organisations/hm-treasury
How the Ten-Year Threshold Actually Counts
The counting mechanism matters enormously for planning. Specifically, the test looks back over the previous twenty tax years and asks whether you were UK tax resident in at least ten of them. Therefore, a US executive who arrived in London in 2015 and remained resident throughout became a long-term resident on 6 April 2025. Meanwhile, someone who arrived in 2020 will not cross the threshold until the 2030-31 tax year, assuming continuous residence.
Importantly, residence is determined under the Statutory Residence Test, which counts days, ties, and work patterns. As a result, borderline years demand careful record-keeping. Furthermore, split years and treaty tie-breakers can influence the count, so precise analysis is essential for anyone near the ten-year mark.
https://www.gov.uk/inheritance-tax
The Inheritance Tax Tail That Follows You Home
Leaving Britain No Longer Provides an Immediate Escape
Perhaps the most overlooked feature of the long-term resident inheritance tax regime is its tail. Previously, losing deemed domicile could happen relatively quickly after departure. Now, once you become a long-term resident, you remain within the scope of UK inheritance tax for a period after you leave — even if you return to the United States permanently.
The length of this tail depends on how long you were resident. Specifically, an individual resident for between ten and thirteen years carries a three-year tail. Thereafter, each additional year of residence adds one further year to the tail, up to a maximum of ten years for those resident for twenty years. Consequently, a long-serving American executive who repatriates to New York could remain exposed to 40% UK inheritance tax on their global estate for a full decade after boarding the flight home.
Planning Around the Tail Requires a Long Runway
Because the tail can stretch to ten years, exit planning must begin years before departure. Therefore, high-net-worth families cannot treat inheritance tax as a problem to solve on the way out. Instead, they must model the tail alongside US estate exposure and lifetime gifting strategy. Moreover, the timing of asset transfers, trust settlements, and even the disposal of UK situs property should align with the tail rather than the departure date. Our team routinely builds multi-year exit maps for clients in exactly this position.
https://www.icaew.com/insights/viewpoint-article/2024/feb-2024/tax-guide-for-expats
How UK Inheritance Tax Interacts With US Estate Tax
Two Systems, Two Very Different Exemptions
The collision between the long-term resident inheritance tax rules and the US federal estate tax defines the risk for American clients. On the US side, the federal estate tax exemption stands at $13.99 million per individual for 2025, meaning most estates escape federal tax entirely. On the UK side, the nil-rate band remains frozen at just £325,000, with a further £175,000 residence nil-rate band where a home passes to direct descendants.
Therefore, a wealthy American who becomes a long-term resident may owe no US estate tax at all, yet face a substantial 40% UK inheritance tax bill on the same assets. This asymmetry catches many families by surprise. Furthermore, the UK charge applies to worldwide assets, so US real estate, retirement accounts, and closely held businesses all enter the calculation.
https://www.irs.gov/businesses/small-businesses-self-employed/estate-tax
https://www.investopedia.com/terms/i/inheritancetax.asp
The US-UK Estate and Gift Tax Treaty as a Shield
Fortunately, the US-UK estate and gift tax treaty exists precisely to prevent the same assets being taxed twice. The treaty allocates taxing rights between the two countries and provides credits to relieve double taxation. Consequently, where both systems apply, one country generally grants a credit for tax paid to the other. Nevertheless, the treaty is technical, and the credit mechanics depend on asset type, situs, and the order in which the two charges arise.
Notably, the treaty can also help determine primary taxing rights over certain assets, which matters greatly for those near the long-term resident threshold. Accordingly, sophisticated estate planning for dual-exposed clients should always start with a treaty analysis rather than a domestic-law calculation alone.
https://www.gov.uk/government/organisations/hm-revenue-customs
Trusts, Businesses and the New Rules
Excluded Property Trusts Have Changed Fundamentally
Before the reform, non-domiciled individuals frequently used excluded property trusts to shelter foreign assets from UK inheritance tax indefinitely. Under the long-term resident inheritance tax regime, however, the protection now depends on the settlor's residence status rather than domicile at the time the trust was created. Therefore, existing structures require urgent review.
Where a settlor is a long-term resident, non-UK assets within the trust can fall inside the relevant property regime, triggering ten-year anniversary charges and exit charges. Consequently, many trusts established under the old rules no longer deliver the shelter their creators intended. Moreover, for American settlors, these UK trust charges sit alongside the US grantor trust rules, creating a genuinely intricate compliance picture.
https://www.ciot.org.uk/tax-guidance
Business and Agricultural Relief Still Matter
For US business owners overseas, business relief remains a valuable planning tool despite the wider reform. Qualifying trading businesses can still attract up to 100% relief from UK inheritance tax, subject to the reforms taking effect from April 2026 that cap the fully-relieved amount. Therefore, entrepreneurs holding qualifying UK or overseas trading interests should revisit their structures now.
Additionally, the interaction with US tax on the same business interests demands care. Specifically, valuation, entity classification, and the timing of any transfer all influence the combined UK and US outcome. As a result, coordinated advice across both jurisdictions consistently outperforms siloed planning.
https://www.state.gov/citizenship/american-citizens-abroad/
Case Study: A Long-Term Resident Inheritance Tax Scenario
Consider James, a fictional but representative client. James, a US citizen, moved from Chicago to London in 2013 to run the European division of a technology group. By 6 April 2025, he had been UK resident for twelve consecutive tax years. Consequently, he became a long-term resident, bringing his entire worldwide estate within the scope of UK inheritance tax.
James holds substantial wealth: a £2.4 million home in Kensington, a US brokerage portfolio worth $6 million, a Chicago rental property valued at $1.4 million, and a 30% stake in a private US company worth approximately $4 million. In total, his worldwide estate exceeds £11 million. Under US rules, his estate sits comfortably below the $13.99 million federal exemption, so he anticipated little estate tax exposure.
However, the long-term resident inheritance tax regime changes everything. Because James is now a long-term resident, HMRC can charge 40% inheritance tax on his worldwide estate above the £325,000 nil-rate band. Therefore, on a taxable estate of roughly £10.7 million, the potential UK inheritance tax liability approaches £4.28 million — a charge he simply did not face under the old domicile rules while he remained a non-dom.
Fortunately, the US-UK estate and gift tax treaty provides meaningful relief on the US-situs assets, and careful structuring can reduce the exposure further. Specifically, our team modelled a strategy combining lifetime gifting with survivorship, a review of his US company stake for business relief, and a restructuring of a legacy trust that no longer qualified as excluded property. As a result, James's projected UK inheritance tax exposure fell by more than £1.6 million, while his US position remained fully compliant. Moreover, we mapped his ten-year tail so that any future return to Chicago aligns with the optimal exit window rather than an arbitrary date.
https://www.irs.gov/individuals/international-taxpayers/streamlined-filing-compliance-procedures
https://www.moneyhelper.org.uk/en
How TaxYork Can Help
TaxYork specialises in the precise intersection where the long-term resident inheritance tax regime meets the US federal estate tax. Our team works exclusively with Americans abroad and US business owners overseas, so we understand both systems intimately. Furthermore, we coordinate UK and US analysis under one roof, which prevents the costly gaps that arise when advisers work in isolation.
We begin every engagement with a residence-and-exposure audit, establishing exactly where you sit against the ten-year threshold and the tail. Thereafter, we build a treaty-led estate plan that harmonises lifetime gifting, trust structuring, business relief, and US grantor trust compliance. Additionally, we handle the ongoing reporting obligations that follow, from FBAR and FATCA filings to US estate and gift tax returns. You can explore our dedicated support for American families through our specialist services.
https://www.taxyork.com/services/us-expat-tax/
https://www.taxyork.com/services/estate-planning/
Conclusion
The long-term resident inheritance tax reform has rewritten the rules for wealthy Americans living in Britain. Consequently, families who once relied on non-dom status to shelter worldwide wealth now face 40% UK inheritance tax across their entire global estate once the ten-year threshold bites. Moreover, the tail means that leaving the country no longer offers a quick escape, and legacy trust structures may no longer deliver the protection they were built to provide.
Nevertheless, thoughtful planning still achieves substantial savings. Specifically, treaty relief, lifetime gifting, business relief, and coordinated UK-US structuring can materially reduce exposure when implemented early. Therefore, the worst response is to wait. Instead, high-net-worth Americans in Britain should model their position now, before the tail lengthens and options narrow. Ultimately, the families who act early keep control; those who delay hand it to two tax authorities at once.
Contact Us
Speak to our specialists about your long-term resident inheritance tax position and estate strategy. Email hello@taxyork.com or call 020 3488 8606. Alternatively, visit our website to arrange a confidential consultation with a US-UK cross-border tax specialist.
https://www.taxyork.com/contact/
Disclaimer
This article is provided for general information only and does not constitute tax, legal, or financial advice. Tax rules are complex, subject to change, and depend on individual circumstances. Accordingly, you should not act, or refrain from acting, on the basis of this content without obtaining professional advice tailored to your situation. TaxYork accepts no liability for any loss arising from reliance on this article. All figures, thresholds, and case studies are illustrative and current at the time of writing.