Cross-Border Inheritance Tax: Estate Planning When Your Family Spans Jurisdictions

Let's talk about a problem that arrives at the worst possible moment, when nobody in the family is thinking about tax returns. You built a life across borders: a house in one country, an investment account in another, perhaps a passport that doesn't match your address. Then someone dies, and suddenly two or three governments show up at the funeral with an invoice. This is the world of cross-border inheritance tax, and if your family and your assets sit in more than one country, it is coming for you whether you plan for it or not.

The good news is that this is a solvable engineering problem. The bad news is that solving it after death is close to impossible, and the systems involved (particularly in the US, UK, and Spain corridors) have all been rewritten in 2025 and 2026 in ways that punish the unprepared. What follows is how the machine actually works, where it bites, and what you can do while you are still around to sign documents.

Why dying with assets in two countries is a tax problem

Every country that wants to levy an international estate tax on a death needs a legal hook. There are three of them, and understanding the difference is the whole game.

• Situs: The physical or legal location of an asset. A villa in Marbella has Spanish situs. Shares in a US corporation have US situs. Situs is the most primal claim there is. If the asset sits inside a country's borders, that country claims the right to tax its transfer on death regardless of where you lived or what passport you held. This is why a resident of London can be taxed by Madrid, and a resident of Barcelona can be taxed by Washington.
• Domicile: A common law concept meaning your permanent, ultimate home. It is rooted in intention, not just physical presence. You can live abroad for decades and still be domiciled where you intend to eventually return. Historically this was the bedrock of both US and UK estate tax, deciding whether a country taxed your worldwide assets or just the local ones.
• Residence: The objective, mathematical test favored by civil law countries like Spain and, as of 2026, increasingly by the UK. It counts days and looks at where your center of vital interests actually sits, and it politely ignores your subjective feelings about "home".

The collision happens like this. Country A decides you are domiciled or resident there and taxes your entire global estate. Country B notices you own an asset inside its borders and taxes that same asset on situs. Now the same house or the same share portfolio is being taxed twice, by two sovereigns who do not answer to each other. That is inheritance tax in two countries, boiled down to one sentence, and the rest of this article is about surviving it. If you want the broader strategic picture, our overview of international estate planning covers the ground above the tax mechanics.

The UK angle: domicile, 40% inheritance tax, and the shift to residence

For over a century the UK ran its inheritance tax (IHT) on domicile. A foreign national could live in London for years as a "non-dom" and keep their non-UK assets outside the 40% charge, right up until the old deemed-domicile trap caught them at 15 out of 20 years of residence. That world is gone.

Effective 6 April 2025, the UK abolished the non-dom regime and switched to a residence test. Under the 2026 framework, your worldwide estate becomes exposed to 40% IHT (above the frozen £325,000 nil-rate band) once you become a Long-Term Resident, which now means UK tax resident for 10 out of the previous 20 years. That accelerates the global dragnet by five years compared to the old rule.

Then there is a wrinkle most people do not expect. When you leave the UK, the tax does not leave with you. The new regime attaches an "IHT tail," a period after departure during which your worldwide estate stays fully exposed to UK IHT even though you no longer live there. The tail is graduated by how long you were resident:

1. Under 10 years of residence: no tail, non-UK assets are exempt the moment you leave.
2. 10 to 13 years: a 3-year tail.
3. 15 years: a 5-year tail.
4. 20 or more years: the maximum 10-year tail.

Picture Sarah, who lived in the UK for two decades and then retired to the Spanish coast. She carries the full 10-year tail. If she dies in year nine of her Marbella retirement, her entire global estate is still subject to 40% UK IHT, as if she never left. And UK-situs assets like London property stay in the net permanently regardless of where she lives.

The 2025/2026 reforms also closed the escape hatches. Business Property Relief and Agricultural Property Relief, which used to give 100% exemption on family firms and farms, are now capped at £1 million of qualifying value, with anything above that getting only 50% relief. From 6 April 2027, most unused pension funds get pulled into the taxable estate too, ending the pension's long run as the quiet way to pass money down a generation.

The US angle: the estate tax and the $60,000 situs trap

The US system is the strange one, because it taxes on citizenship. An American citizen owes US estate tax on their worldwide assets no matter where they live or die. The One Big Beautiful Bill Act, signed in July 2025, set the lifetime estate and gift exemption permanently at $15 million per person, or $30 million for a married couple using portability, effective 1 January 2026, indexed for inflation from 2027. The top rate sits at 40%. For an American family, that exemption shelters nearly every estate from federal tax.

The part that catches foreign investors off guard is what happens if you are a Non-Resident Alien, meaning neither a US citizen nor a US domiciliary. The US then taxes you only on your US-situs assets, and your federal exemption is not $15 million. It is $60,000, not a typo, and the gap between the two numbers is where most of the damage happens.

Everything above that $60,000 of US-situs wealth is taxed on a rising scale up to 40%. And "US-situs" is defined in ways that are counterintuitive enough to be dangerous. Consider John, a British citizen living in Spain, who dies owning $1 million of Apple stock through his London brokerage account. He never set foot in America to buy it, and the shares sit in a European account. None of that changes the answer. Stock issued by a US corporation is US-situs for estate tax purposes, including US-domiciled ETFs and mutual funds, regardless of where the account or the certificates sit. The IRS can legally claim 40% of the value above $60,000, and his executor has to file Form 706-NA to sort it out. Until the IRS issues a transfer certificate, US institutions are barred from releasing the funds to his heirs.

The code does hand out some deliberate exemptions to keep foreign capital flowing in. These bypass US estate tax entirely for a Non-Resident Alien:

• US bank deposits: ordinary cash in a US commercial bank account.
• US Treasury securities and most publicly traded US corporate bonds under the portfolio interest exemption.
• Life insurance proceeds on the life of the Non-Resident Alien.

The difference between holding $1 million in Apple shares and $1 million in the right structure is the difference between a 40% haircut and zero. That gap is entirely a planning problem, and it is why situs-aware structuring, which our work on asset protection trusts touches on, matters so much for globally invested families.

Spain: succession tax that varies sharply by region

Spain does something different from both. Its Impuesto de Sucesiones y Donaciones (ISD) is not an estate tax on the deceased, it is an acquisition tax on the person who inherits. It is triggered either because the beneficiary is a Spanish tax resident, or because the asset sits in Spain (a Costa del Sol villa, a Madrid bank account) even when the heir lives abroad.

The federal rates run from 7.65% up to 34%, but almost nobody pays those, because Spain's 17 autonomous communities can slash them with their own reductions, known as bonificaciones. This is where geography becomes strategy:

• Andalusia: 99% relief for close family, plus a €1 million personal allowance.
• Madrid: 99% relief on inheritances and gifts.
• Balearic Islands: up to 100% relief for spouses, children, and parents.
• Canary Islands: 99.9% relief for close family.
• Valencia: 99% for close family, with new sibling relief phasing in from 2026.
• Catalonia: notably stricter, with much lower allowances.

For a long time these regional gifts were reserved for locals, and non-residents got hammered with the punitive federal rates. Then the EU Court of Justice struck that down in 2014, and a 2018 Supreme Court ruling (codified by Law 11/2021) extended equal treatment to residents of countries outside the EU too. So as of 2026, a post-Brexit Briton or a US expat has the same right as any local to apply the rules of the region where their highest-value Spanish assets sit. Where you buy the villa now materially changes the tax bill.

Two more layers apply to Spanish real estate. The municipal plusvalía taxes the theoretical increase in land value, and since 2021 you may choose between a real-gain method and an objective method, picking whichever is lower. Separately, the Temporary Solidarity Tax on Large Fortunes hits net worldwide wealth above €3 million at 1.7% to 3.5%, a federal floor designed specifically to stop regions like Madrid from competing wealth tax down to zero.

And then the operational trap that hurts the most: Spanish inheritance tax must be calculated, filed, and paid in cash within six months of death. The authorities freeze the deceased's accounts and block the notary from transferring the property until the tax is paid. So the heirs cannot sell the villa to pay the tax, because they do not legally own the villa until the tax is paid. Property-rich, cash-poor estates get forced into bridging loans or fire sales. Foreign heirs also need a Spanish NIE number to deal with the tax office, and that can take two to six months to obtain, eating straight into the same deadline.

When inheritance tax applies in two countries at once

Double taxation on death happens the moment a personal-status claim overlaps a situs claim. It would be convenient if the systems simply talked to each other and netted out the difference. In practice they rarely do.

A UK Long-Term Resident dies owning a Marbella villa: Spain taxes it on situs, and the UK taxes the very same villa because LTR status reaches worldwide. Two governments end up claiming the same asset, and neither recognizes the other's prior claim. Relief exists, but it is partial and it is fiddly, and the gap it leaves is real money.

Relief mechanisms: treaties, unilateral credits, and their limits

There are two ways to claw back a double hit. The clean way is a bilateral estate tax treaty. The messy way is unilateral relief written into each country's domestic law.

The US and UK have an unusually powerful instrument here: the 1979 US-UK Estate and Gift Tax Treaty. Its Article 4 tie-breaker sorts out who has the primary claim when both countries consider you theirs, and for a US citizen who is not also a UK national, a mechanical seven-year rule can tie-break domicile back to the US. The treaty even severs the UK IHT tail in the right circumstances. Take an American who lived in London 15 years and moved back to New York in 2025, carrying a 5-year UK tail. On death in New York they are US-domiciled under the treaty, and because they are not a UK national, Article 5 overrides domestic UK law and eliminates UK tax on their non-UK assets. The treaty also lets a UK domiciliary's estate claim a pro-rata slice of the full $15 million US exemption instead of the bare $60,000, scaled by the ratio of US-situs assets to the worldwide estate.

The UK-Spain and US-Spain corridors have no such treaty. Income tax agreements exist, but they do not cover inheritance or estate tax, so you fall back on unilateral relief. And unilateral relief is capped in a way that quietly leaves value on the table. Under UK law, IHTA 1984 section 159 gives a credit for foreign death tax on foreign property, but only up to the portion of UK IHT attributable to that specific asset.

Here is how the gap opens. Bernice is a UK Long-Term Resident with a £300,000 global estate that generates a £20,000 UK IHT bill. Inside it is a £50,000 Spanish apartment, on which the Spanish authorities charge her heirs £4,000. The UK credit is calculated by a fraction: £50,000 divided by £300,000, multiplied by the £20,000 total, which comes to £3,333. Her family paid £4,000 in Spain but the UK will only credit £3,333. The remaining £667 is genuine double taxation that no mechanism recovers, and that same proportional gap applies at any size of estate. On a seven-figure estate, the uncovered amount becomes a material sum.

There is also a structural mismatch that makes even the available relief hard to claim. UK IHT is paid centrally by executors out of the estate. Spanish ISD is paid personally by each beneficiary out of their own pocket. Lining up those individual Spanish receipts against a single UK estate return takes deliberate, synchronized cross-border accounting, or the relief simply does not get recognized.

Structuring ahead of time: trusts, situs, gifting, and insurance

Passive holding is the losing move. If you own the wrong assets in the wrong wrapper across these three countries, the math erodes the estate on its own. Expat estate planning means structuring while you still can, and the right tool depends heavily on the corridor.

• Trusts, handled with care. Trusts remain the backbone of US and UK planning, but they travel badly. For a US citizen married to a non-citizen, the unlimited marital deduction is disallowed, which threatens a 40% hit on the first death. The statutory fix is a Qualified Domestic Trust (QDOT), which defers the US estate tax until the surviving spouse draws down or dies, provided at least one trustee is a US person and, above $2 million, a US bank serves as trustee or a bond is posted. For a UK Long-Term Resident, though, settling a trust now triggers a 20% entry charge under the relevant property regime, and a US-style revocable grantor trust trips the UK's Gift with Reservation of Benefit rules, dragging the assets back into the 40% estate. Our deeper look at offshore trusts walks through where these structures still earn their keep and where they backfire.
• Keep Spanish assets out of trust entirely. Spain is a civil law country and does not recognize trusts. Put a Spanish villa inside a UK or US trust and the tax authorities look straight through it, treat the beneficiaries as direct owners, and, worse, break the family kinship link that the 99% regional reliefs depend on. The result is the full 34% state rate on an asset that should have paid almost nothing. Hold Spanish-situs assets directly, or through a compliant Spanish holding company.
• Situs planning and lifetime gifting. Much of the US NRA exposure is a situs problem you can design around, swapping directly-held US shares for exempt instruments or non-US-situs holding structures. Lifetime gifting still helps at the margins, though note the annual gift exclusion is only $19,000 per recipient and gifts to a non-citizen spouse are capped at $194,000 a year.
• Insurance as the liquidity engine. Because civil law systems respect insurance contracts, insurance wrappers have become the cleanest cross-border tool. Private Placement Life Insurance (PPLI), aimed at families with $10 million-plus, makes the insurer the legal owner of the underlying portfolio, which compounds free of income and capital gains tax and pays out a tax-free death benefit that can sidestep both US estate tax (inside an ILIT) and UK relevant property charges. For UK expats in Spain specifically, a Spanish Compliant Bond written joint-life last-survivor triggers no tax on the first death, passes to named beneficiaries outside probate, and is generally exempt from Spanish wealth and solidarity tax. And both solve the six-month liquidity trap, because the death benefit arrives as cash, directly to the heirs, exactly when the Spanish tax office wants paying.

One more structural point that sits underneath all of this: use concurrent, jurisdiction-specific wills, not one global will. A single worldwide will invites conflicting interpretations, sworn translations, and apostille costs, and a standard "I revoke all previous wills" clause in a later UK will can silently void an earlier Spanish one. For assets in Spain, an expat can also make a Brussels IV election (a professio iuris) choosing the law of their nationality to escape Spanish forced heirship, which otherwise reserves two-thirds of the estate for children. But that election cuts both ways: HMRC treats an explicit choice of English law as evidence of enduring UK ties, so a clause meant to fix your Spanish succession can quietly reinforce the UK domicile you were trying to shed. Coordinating these documents is exactly the kind of work our private client and family office practice exists to handle, because the pieces only protect you if they are drafted to point in the same direction.