UK-US Cross-Border Inheritance: Wills, Tax & Estate Planning

For a family whose members, homes, and assets are split between the UK and the US, succession is not simply a matter of writing a will. Two legal systems govern how wills are made and honoured, how estates pass through probate, and how heirs are taxed - and they do not automatically fit together. The result is that ordinary estate planning, done for one country in isolation, can leave gaps that fall on grieving relatives at the worst possible time.

This article is for families with members,heirs, or assets across the UK and the US who are thinking about wills,beneficiaries, and succession.

Two legal systems, one family

The UK and US approach wills and inheritance differently - in the formalities required, in how estates are administered, and in how much freedom you have to leave assets as you wish. A will drafted to be valid and effective in one country may be cumbersome, or partially ineffective, in the other. Recognising that your estate may need to satisfy two systems is the starting point, and it is why cross-border families so often need more than a standard domestic will.

One will or two?

A common question is whether to have a single worldwide will or separate 'mirror' wills in each country. Each approach has trade-offs. A single will can be simpler to maintain but slower and more complex to administer across two probate systems. Separate wills can streamline administration in each country but carry a real risk: a later will can unintentionally revoke an earlier one if they are not carefully drafted to coexist. Getting this wrong can leave part of an estate governed by no valid will at all. This is an area where coordinated legal drafting in both countries matters.

Cross-border beneficiaries

Who inherits, and where they live, shapes the tax and reporting consequences. A US person inheriting UK assets brings those assets into the US system, with potential reporting obligations and, for some structures, foreign-trust complications. A UK person inheriting US-situated assets may face US estate tax exposure on those assets. Gifts during life carry their own cross-border rules. The point is that an inheritance is not only an event for the person leaving the assets; it lands on the recipient's tax position too, and planning that ignores the beneficiary's side misses half the picture.

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The tax overlay

Sitting over all of this is the interaction of UK inheritance tax and US estate tax, coordinated by the US–UK estate tax treaty, which is covered in detail in the pillar article for this series. For succession planning, the practical implication is that the value passing to heirs depends not just on what you leave but on how the two tax systems treat it - and on whether the treaty's reliefs have been considered.

Currency and liquidity

A frequently overlooked issue is simply paying the tax. Estates connected to both countries may owe tax in both, on different timetables, in different currencies. If the estate's wealth is tied up in property or illiquid assets, heirs can face tax bills before they can access the money to pay them. Planning for liquidity - and for the currency in which obligations fall due - is part of a cross-border estate plan, not a detail to leave to chance.

An illustrative example

Consider a hypothetical family with a UK parent, a US-resident adult child, a London home, and a US investment account. Without coordinated wills, the parent's later US will risks revoking an earlier UK one; the US-resident child's inheritance of UK assets raises US reporting; and the estate could owe tax in both countries before the London property can be sold to fund it. With coordinated drafting, beneficiary-side planning, and attention to liquidity, the same estate passes far more smoothly. This example is hypothetical and for illustration only.