Domicile and UK Inheritance Tax: Explained for Wealthy US-UK Dual Filers
For decades, the way the UK IHT domicile rules worked decided whether a wealthy American in Britain faced 40% inheritance tax on their worldwide estate or only on their UK assets. From 6 April 2025, domicile no longer drives that outcome: a residence-based test does, and the shift rewrites the planning map for every US-UK family.
Why is domicile used to decide everything?
Wealthy transatlantic families rarely worry about a single tax system. An American partner at a London fund, a US-born founder who moved to the UK a decade ago, a couple splitting the year between New York and the Cotswolds — each sits inside two death-tax regimes at once.
UK inheritance tax applies tos the estate under one set of rules; US estate tax applies tos it under another. Getting the interaction wrong can hand two governments 40% of the same assets.
Under the system that ran until April 2025, the pivot was domicile rather than residence.
Domicile is a common-law concept: broadly, the country you treat as your permanent home and intend to return to. A person born to an American father typically acquired a US domicile of origin, and shedding it required genuinely severing ties and forming a settled intention to remain in the UK indefinitely.
That single status governed how far UK inheritance tax could reach. Our primer on UK inheritance tax basics covers the nil-rate bands and rates that still apply today.
How did the old UK domicile IHT rules work?
Taxpayers were divided into two groups by the previous UK IHT test. A UK-domiciled individual was exposed to inheritance tax on their worldwide assets. A non-domiciled individual — a "non-dom" — was exposed only to UK-situs assets: UK land, UK company shares, UK bank accounts, and similar property. Everything held offshore sat outside the net.
That gap made domicile the single most valuable status in transatlantic estate planning. An American who kept a US domicile could hold a large offshore portfolio entirely free of UK inheritance tax. At the same time, a genuinely UK-domiciled person paid UK IHT on the same holdings wherever in the world they sat.
The standard rate stayed the same for both — 40% above the nil-rate band — but the base it applied to was worlds apart.
To stop long-stayers claiming non-dom status indefinitely, the rules bolted on "deemed domicile". Anyone who has been a UK resident for at least 15 of the previous 20 tax years is treated as UK domiciled for inheritance tax, as are certain returning UK domiciles.
Once deemed domiciled, worldwide exposure followed. We unpack the mechanics in our guide to deemed domicile explained, and HMRC's own summary of the pre-April-2025 deemed domicile rules remains a useful reference for estates spanning the transition.
The Old Testament at a glance
Status (pre-6 April 2025)
UK IHT reach
UK-domiciled
Worldwide assets
Non-domiciled
UK-situs assets only
Deemed domiciled (15 of 20 years)
Worldwide assets
The 2025 reform: from domicile to long-term residence
On 6 April 025, the government replaced the domicile-connected factor with a residence-based one. The concept of domicile — and deemed domicile — was switched off for inheritance tax. In its place sits a single question: is the individual a "long-term resident"? Anyone still framing their affairs around the old domicile UK IHT language is now working from a repealed rulebook.
UK-situated assets remain inside the net for everyone, exactly as before. What changed is the test for non-UK assets. Instead of asking where a person is domiciled, HMRC now asks how long they have lived here, using the same statutory residence test that already governs income tax and capital gains tax.
Who counts as a long-term resident?
After a person has lived in the UK for at least ten of the twenty tax years before to the year of a chargeable event, typically death or a gift into trust, arises. Cross-lineal and worldwide assets under the UK inheritance tax. Stay below it, and only UK-situs assets are caught. This is the residence-based successor to the old domicile UK IHT worldwide charge, and HMRC sets it out in its guidance on inheritance tax for long-term UK residents.
The 10-year threshold bites far faster than the old 15-year deemed domicile clock. A US executive who arrives in London and settles in for a decade now brings their entire global estate into UK inheritance tax two full tax years earlier than the previous regime would have. For an in-depth walk-through of the wider changes, see our note on the UK non-dom FIG regime.
The departure "tail"
Leaving the UK no longer switches worldwide exposure off overnight. A long-term resident who departs stays inside the net for a "tail" that runs from three to ten years, scaled to how long they lived here. Someone who has resided for 10 to 13 of the past 20 years faces the minimum three-year tail; each additional year of residence adds a year, up to a ten-year maximum. A person who has been UK-resident for 17 of 20 years on departure, for example, carries a seven-year tail. The clock resets only after ten consecutive tax years of non-residence.
Years UK-resident (of last 20)
Post-departure IHT tail
10 to 13 years
3 tax years
15 years
5 tax years
17 years
7 tax years
20 years
10 tax years
Where UK inheritance tax collides with US estate tax
For Americans, the reform matters twice over because the US estate tax never went away. The United States taxes the worldwide estates of its citizens and domiciliaries, regardless of where they live, at rates up to 40%. The federal estate tax carried a lifetime exclusion of $13.99 million per person in 2025, rising to $15 million from 2026 — generous, but no help against a UK charge that starts once an estate tops £325,000.
Layer the two regimes, and the risk is obvious: the same worldwide estate can be pulled into UK inheritance tax under the long-term residence test and into US estate tax under citizenship. A newly caught long-term resident who once relied on the old domicile UK IHT exemption for offshore holdings may now see those assets taxed on both sides of the Atlantic unless relief is claimed.
The safety valve is the US-UK estate and gift tax treaty. It allocates taxing rights between the two countries, resolves conflicts over where an asset is situated, and provides credits so that tax paid in one country offsets tax due in the other. The full treaty text sets out the tie-breaker rules, and our dedicated explainer on the US-UK estate tax treaty shows how the credit ordering works in practice.
How the nil-rate bands fit in
The UK side keeps its familiar architecture. The nil-rate band stands at £325,000, and a residence nil-rate band of up to £175,000 can apply where a home passes to direct descendants, subject to a taper for larger estates — the mechanics are set out in HMRC's guidance on passing on a home. Anything above the available bands is charged at 40%. Unlike the US exclusion, these thresholds are modest, which is why worldwide exposure is the number that keeps wealthy families awake.
Planning after the reform
Three levers matter most now—first, timing. Because the long-term resident clock counts 10 of the last 20 tax years, the dates of arrival and departure carry real money — a family planning a move should model the residence position years ahead, not in the final weeks. HMRC's residence and domicile guidance is the starting point for mapping the timeline.
Second, structures. Excluded-property trusts — long the workhorse of non-dom planning — changed fundamentally under the reform, with protection now tied to the settlor's long-term resident status rather than their domicile at the time the trust was funded.
Trusts settled while outside the net can behave very differently from those funded after the settlor became a long-term resident; our guide to excluded-property trusts covers the transitional traps.
Third, the treaty. For US citizens, no UK plan is complete without checking how each step reads on the American return. Gifting, trust funding, and situs choices that reduce UK inheritance tax can trigger US gift tax or result in a step-up in basis. Coordinating both sides — rather than optimizing one and hoping the other follows — is the whole discipline of cross-border estate planning.
Life insurance written in trust also deserves a mention. A well-structured policy can fund the eventual inheritance tax bill without itself forming part of the taxable estate, giving heirs the liquidity to settle the charge rather than forcing a fire sale of the family home or an illiquid business stake. For Americans, the policy's treatment on the US return has to be checked in parallel, since a structure that is clean for UK purposes is not automatically efficient across the Atlantic.
Case study: The Harpers
Consider Daniel and Beth Harper, US citizens who moved from Boston to London in 2013 and never left. By the 2025-26 tax year, they had been UK-resident for 12 consecutive years — comfortably over the 10-of-20 threshold, so both are long-term residents. Their $18 million estate — a London home, a US brokerage account and a Delaware LLC — is now within UK inheritance tax worldwide, not just on the UK house.
Under the old regime, Daniel and Beth might still have argued a US domicile of origin and sheltered the offshore assets; the residence test removes that argument entirely. Their planning instead runs through the treaty: UK inheritance tax applies first on death, and the US allows a credit for the UK tax paid, preventing the full 40%-on-40% double hit. If they later retire to Boston, each carries a three-year tail before their worldwide estate leaves the UK net. Mapping that exit — and funding any trust before, not after, a return — is where the real saving sits.
Talk to TaxYork
Cross-border estate planning rewards early, coordinated advice and punishes guesswork. If you are a US citizen or dual filer weighing how the new residence test affects your estate, our specialists model both sides together. Email hello@taxyork.com, call 020 3488 8606, or visit taxyork.com to arrange a consultation.