Estate and Investment Planning Around Marrying a UK National
Sound estate investment planning for a UK national starts with one uncomfortable fact: US tax law treats a non-US-citizen spouse very differently from a citizen spouse. The unlimited marital deduction disappears, gift rules tighten, and the couple's joint accounts create new US reporting—plan before the wedding, or shortly after, to avoid an unexpected 40% estate tax bill.
Why does marrying a UK national change your US tax position?
When two US citizens marry, wealth can pass between them freely during life and at death. That independence drastically decreases as soon as one spouse is a citizen of the United Kingdom and not the United States.
The US Internal Revenue Code links its most generous spousal relief to citizenship, not to marriage, so a US person who marries a UK national inherits a set of rules built on the assumption that assets left to a foreign spouse could leave the US tax net entirely. To stop that, Congress replaced the usual reliefs with deferral mechanisms and caps.
The picture is a two-country one. The US taxes its citizens and green-card holders on worldwide assets, while the UK now taxes based on long-term residence. Getting estate investment planning right when marrying a UK national means reconciling both systems at once, because a step that saves UK inheritance tax can trigger US estate tax, and vice versa.
The three moving parts
Every cross-border couple is really juggling three things: the estate rules that decide what happens at death, the gift rules that govern lifetime transfers, and the investment and reporting rules that apply to the accounts they hold along the way. Treat them separately, and you will miss the traps that sit between them.
How the US estate tax marital deduction fails a non-citizen spouse
Between US citizen spouses, the unlimited marital deduction allows the first spouse to die to leave everything to the surviving spouse without US estate tax. That deduction is switched off where the surviving spouse is not a US citizen. Without planning, assets above the exclusion amount, which stands at $13.99 million per person for 2025, are subject to the US estate tax at a top rate of 40%. A UK national widow or widower could therefore face a large US bill on wealth that a citizen spouse would have received tax-free.
The intended fix is the Qualified Domestic Trust, or QDOT, under Section 2056A. Property passing into a QDOT for the non-citizen spouse qualifies for the marital deduction, so the estate tax is deferred rather than paid on the first death.
The trust must have at least one US trustee, must withhold estate tax on capital distributions, and comes with strict security rules once its value exceeds $2 million. It is the backbone of most estate investment planning marrying a UK national, and it needs drafting properly — a bare bequest to a foreign spouse gets no deferral at all. Our guide to a QDOT for a non-citizen spouse walks through the mechanics.
Scenario
US citizen spouse
Non-US-citizen (UK national) spouse
Bequest at death
Unlimited marital deduction
No deduction unless a QDOT is used (§2056A)
Lifetime gift between spouses
Unlimited, tax-free
Capped annual exclusion ($190,000 for 2025)
US estate tax rate is above the exclusion
40%
40%
2025 US exclusion per person
$13.99 million
$13.99 million
What are the lifetime gift limits with a non-citizen spouse?
Lifetime giving is squeezed in the same way. A gift from one US citizen spouse to another is unlimited. A gift to a non-citizen spouse instead uses a special, capped annual exclusion of $190,000 for 2025, indexed each year. Anything above that draws on the giver's lifetime exemption and must be reported on Form 709. The IRS gift tax rules are unforgiving here, and couples often trip over them when funding a joint home purchase or moving cash into a spouse's sole account.
Read our note on gifts to a non-citizen spouse before making any large transfer.
Prenuptial and postnuptial planning matters more in this setting than most couples expect. A prenuptial agreement can ring-fence pre-marriage assets, document who owns what, and make later gift and estate reporting far cleaner.
Beneficiary designations on pensions, life policies, and retirement accounts should be reviewed at the same time, because an outdated form can send assets to a non-citizen spouse outside the QDOT and undo the deferral you paid to build.
How does the 2025 UK inheritance tax reform affect a US-UK couple?
The UK side changed materially from 6 April 2025. Historically, transfers between spouses were exempt from UK inheritance tax. Still, a gift from a UK-domiciled spouse to a non-UK-domiciled spouse was capped, with anything above the nil-rate band potentially taxable unless an election was made. The reform replaces domicile with a residence test. Under the new residence-based IHT rules, a person becomes a "long-term resident" — exposed to UK inheritance tax on worldwide assets — after being UK resident for at least 10 of the previous 20 tax years.
For a US-UK couple, that reframes the question. Where one spouse is a long-term resident, and the other is not, the spouse exemption is still restricted to the £325,000 nil-rate band, but the non-long-term-resident spouse can now elect to be treated as a long-term resident to unlock the full exemption.
The election has consequences — it drags worldwide assets into UK inheritance tax — so it is rarely a free win. Coordinating this with the US position is where good estate investment planning for a UK national earns its keep, and the US-UK estate and gift tax treaty can relieve double taxation when both systems reach for the same asset. We cover the interaction in our US-UK estate tax treaty explainer.
What investment and reporting traps hit the US spouse?
Marriage merges finances, and for a US person, that merger creates reporting exposure. Once your name goes on a UK account — or you gain signature authority over your spouse's account — you may have to file an FBAR and, above higher thresholds, Form 8938. Joint ownership counts. Penalties for missed filings are severe, as we set out in FBAR penalties explained.
The larger investment trap is the PFIC problem.
Most UK pooled investments — unit trusts, OEICs, investment trusts and the funds inside a Stocks and Shares ISA — are passive foreign investment companies in the US's eyes. A US spouse who is treated as owning them faces punitive tax and Form 8621 filing, and the ISA's UK tax shelter is ignored by the IRS entirely.
Careful estate investment planning, marrying a UK national, keeps PFIC-heavy holdings in the UK spouse's sole name, uses US-compliant funds for the US spouse, and avoids joint brokerage accounts that would taint otherwise clean portfolios.
Should you elect to treat the UK spouse as a US resident?
A US person can elect under Section 6013(g) to treat a non-resident spouse as a US resident, allowing a joint return. That can lower US income tax through joint-filing brackets, but it also pulls the UK spouse's worldwide income into the US net and adds their foreign accounts to the reporting pile. For many couples, the cost outweighs the benefit. Weigh it deliberately using the IRS guidance on the nonresident spouse election, and read our breakdown of the Section 6013(g) election before committing, because it is difficult to revoke.
Case study: Daniel and Priya
Daniel, a US citizen and software director living in London, married Priya, a British national and lifelong UK resident. Their combined estate was around $9 million, much of it in Daniel's US retirement accounts and a jointly held London flat. Their first draft wills left everything to each other outright.
On the first death, that plan gave Priya no marital deduction, exposing Daniel's US assets to a potential 40% estate charge, while Priya's ISA quietly sat in Daniel's joint reach as a PFIC reporting problem.
We rebuilt the plan around a QDOT for Priya, separated the ISA into her sole name, replaced Daniel's PFIC funds with US-compliant equivalents, and modeled — but did not make — a long-term-resident election for UK inheritance tax. The estate tax was deferred, the reporting was cleaned up, and both wills now read consistently across two countries.
Action
Problem it solves
QDOT for the UK spouse
Restores the marital deduction and defers US estate tax
ISA and funds into the UK spouse's sole name
Removes PFIC exposure for the US spouse
Prenuptial agreement and updated beneficiaries
Cleaner gift and estate reporting; assets follow the plan
Model the UK long-term-resident election
Decide whether the full UK spouse exemption is worth worldwide IHT
Talk to TaxYork before you say "I do"
Cross-border marriage rewards couples who plan early. If you are approaching a wedding, or already married and unsure whether your wills and accounts still work across the Atlantic, TaxYork can map the US and UK sides together and put the right structures in place. Email hello@taxyork.com, call 020 3488 8606, or visit taxyork.com to arrange a consultation.