UK-US Cross-Border Estate & Gift Tax Treaty Guide 2026

Executive Summary & Dual Estate Tax Regimes

Cross-border estate planning involving the UK and US requires two different systems to be modelled together. For UK Inheritance Tax, the rules changed materially from 6 April 2025: long-term UK residence replaced the former deemed-domicile framework for most new death and lifetime-transfer cases. For US federal estate tax, US citizens and residents can be taxed on worldwide assets, while nonresident noncitizens are generally within the US estate-tax regime only for specified U.S.-situated property, subject to treaty and other relief. Both countries use progressive or threshold-based systems and the UK-US Estate and Gift Tax Convention coordinates taxing rights and credits in defined circumstances.

Comparative Framework: UK HMRC IHT vs US IRS Estate Tax

The table below contrasts estate tax rules between HMRC and the IRS:

The Article 4 Domicile Tie-Breaker Rule

Article 4 of the 1978 UK-US Estate and Gift Tax Convention contains a multi-step fiscal-domicile rule. First, Article 4(1) determines whether the person is domiciled in each country under the treaty definitions. For a U.S. national who is not a UK national, Article 4(3) can deem the person domiciled in the United States if they were not resident in the UK in at least 7 of the 10 income-tax years ending with the relevant year. For a UK national who is not a U.S. national, Article 4(2) contains the corresponding U.S.-residence 7-of-10 test. If the person remains dual-domiciled, Article 4(4) applies the permanent-home, centre-of-vital-interests, habitual-abode, nationality and competent-authority sequence. It is therefore incorrect to describe Article 4 simply as a permanent-home tie-breaker with a seven-year residence rule.

Credit Mechanisms for Double Estate Tax Relief

Article 5 contains the principal treaty taxing-rights rules. Subject to Articles 6 and 7, where a decedent or transferor was domiciled in one Contracting State, property is generally not taxable in the other State unless the special nationality rules apply. Immovable property is addressed by Article 6 and business property of a permanent establishment or fixed base by Article 7. Article 9 then provides the credit mechanism for cases in which both States can tax the same property under the Convention. The credit is limited and is not an automatic guarantee that all double tax disappears.

UK IHT From 6 April 2025 — Long-Term UK Residence

The UK materially changed the basis of IHT from 6 April 2025. The former domicile and deemed-domicile rules were replaced for most new death and lifetime-transfer cases by long-term UK residence. A person is generally long-term UK resident when they have been UK tax resident for at least 10 of the previous 20 tax years. A person who leaves the UK can remain within worldwide IHT for a tail period of between 3 and 10 years depending on their residence history.

UK £325,000 Nil-Rate Band & £175,000 Residence Nil-Rate Band

The standard UK IHT Nil-Rate Band remains £325,000. A Residence Nil-Rate Band of up to £175,000 can apply where the statutory conditions are satisfied, including qualifying residence and direct-descendant inheritance. The RNRB is tapered for estates above £2 million and can interact with transferable allowances and downsizing rules. The £500,000 combined figure should therefore never be described as a universal exemption.

U.S. 2026 Estate & Gift Tax Exemption

For 2026, the U.S. federal Basic Exclusion Amount is $15,000,000 per individual. The applicable credit amount is the federal estate and gift tax credit corresponding to that exclusion amount. The exclusion is unified across lifetime taxable gifts and the estate at death. Therefore, large lifetime gifts can reduce the exclusion remaining at death. The exclusion is not the same thing as the $60,000 filing threshold applicable to many nonresident noncitizens.

U.S. Nonresident Noncitizen — The $60,000 Rule Is Not a $60,000 Exemption

For a decedent who was neither a U.S. citizen nor domiciled in the United States, Form 706-NA is generally required when U.S.-situated assets exceed $60,000 at death. The $60,000 figure is the domestic filing threshold, not a universal amount of estate exempt from U.S. tax. Treaty relief can produce a much larger pro-rata unified credit or exclude property from U.S. taxation altogether, depending on the deceased person's treaty domicile, nationality, the situs of the property and the UK-US Convention.

Article 4 — Correct Fiscal-Domicile Sequence

Article 4 is more detailed than a normal income-tax residence tie-breaker. A U.S. person can be treated as domiciled in the United States under Article 4(1) if resident there or, for a national who is not otherwise resident, if they had been resident there during the preceding three years. A UK person is domiciled in the UK where domiciled under UK law or treated as domiciled for a covered tax. If dual domicile exists, Article 4(2) and (3) apply nationality plus 7-of-10-year residence conditions before Article 4(4) applies the permanent-home and vital-interests sequence.

Article 5 — Treaty Taxing Rights

Article 5 determines which country can tax property after the treaty domicile rules have been applied. Subject to Articles 6 and 7, property is generally taxable only in the state of domicile, except that a national of the other state can preserve taxing rights in certain cases. Article 6 reserves immovable property to source-country taxation, while Article 7 applies to business property of a permanent establishment and assets connected with a fixed base.

Article 8 — Cross-Border Marital Deductions

Article 8 contains the treaty's marital-deduction provisions. Where a UK-domiciled or UK-national transferor passes property that can be taxed in the United States, paragraph 2 allows a U.S. marital deduction to the extent it would have been available if the transferor had been U.S.-domiciled and the estate were limited to U.S.-taxable property. Conversely, paragraph 3 can give a UK spouse exemption equal to 50% of the relevant value in specified cases where the transferor was U.S.-domiciled or a U.S. national and the spouse was not UK-domiciled.

Article 9 — Estate/Gift Tax Credits

Article 9 contains the convention's reciprocal credit rules. The credit depends on which state is imposing tax under the domicile/situs rules and whether the property falls within Articles 6 or 7. The credit is limited to the relevant tax attributable to the property and cannot simply be treated as a blanket credit for all foreign estate or gift tax paid. A claim must also be made within the treaty's stated period.

UK Lifetime Gifts — PETs, 7 Years & Taper Relief

For UK IHT, a potentially exempt transfer to an individual can become exempt if the donor survives seven years. If the donor dies within seven years, the transfer may become chargeable. Taper relief can reduce the amount of IHT payable on a failed lifetime transfer after three years, but taper relief does not reduce the value of the gift itself and does not make every gift tax-free after a particular three-year period. Gifts with reservation of benefit and other anti-avoidance rules can also keep property within the estate.

U.S. Lifetime Gifts — $19,000 Annual Exclusion in 2026

The U.S. annual gift-tax exclusion for 2026 is $19,000 per donee. Gifts above the annual exclusion can still be covered by the lifetime unified estate-and-gift exclusion, but the donor may need to file Form 709 and use part of the applicable exclusion amount. Gifts to a spouse who is not a U.S. citizen have a separate annual exclusion of $194,000 for 2026.

U.S. Citizens Living in the UK — Worldwide Estate

A U.S. citizen remains subject to U.S. federal estate tax on worldwide assets regardless of whether they live permanently in the UK. The U.S. estate is tested under the worldwide gross-estate rules and the applicable exclusion. The UK may also tax the same estate under the long-term UK residence rules. The UK-US treaty then determines domicile, taxing rights and credits where applicable.

UK Long-Term Resident Who Leaves the UK

Leaving the UK does not immediately take a former long-term UK resident outside worldwide IHT. From 6 April 2025, a long-term UK resident can remain within the worldwide IHT regime for between 3 and 10 years after departure, depending on the individual's previous residence history. The exact tail period should be calculated by reference to the 10-of-20 residence record.

Trusts, Settlements & Generation-Skipping Transfers

The UK-US treaty contains specific rules for property held in trusts or treated as comprised in UK settlements. Article 5 excludes certain U.S. generation-skipping trust cases from the ordinary domicile allocation rules and provides separate protections where a U.S.-domiciled settlor who is not a UK national created a settlement. These provisions must be read with each country's trust and generation-skipping rules.

Filing Forms & Treaty-Based Claims

U.S. estate-tax filings depend on the decedent's citizenship/domicile and the value and location of assets. A U.S. citizen or U.S.-domiciled resident generally uses Form 706, while a nonresident noncitizen generally uses Form 706-NA. A treaty-based position can require disclosure, including Form 8833 or the treaty statement requirements described in the Form 706-NA instructions. UK claims are generally handled through the IHT return and HMRC credit/refund processes.

Six-Year Treaty Claim Period

Article 9(5) provides that a treaty-based claim for a credit or refund generally must be made within six years from the date of the event giving rise to the tax liability, or within one year from the latest date on which the tax for which credit is claimed is due, if later. This is an important procedural deadline for cross-border estates and gifts.

Estate-Tax Planning for Non-US-Citizen Spouses

A spouse's citizenship and domicile matter differently in the two countries. U.S. estate tax generally provides an unlimited marital deduction for transfers to a U.S.-citizen spouse, while a noncitizen surviving spouse normally requires QDOT treatment to defer U.S. estate tax on qualifying property. The UK-US treaty contains separate Article 8 rules that can provide special cross-border relief, but those rules do not simply turn every transfer to a foreign spouse into a 100% tax-free transfer.

Practical UK-US Estate & Gift Tax Workflow

A reliable cross-border calculation should identify nationality, UK long-term residence, treaty domicile under Article 4, citizenship/domicile under U.S. estate law, asset situs, trusts/settlements, spouse status, lifetime gifts, and the tax history attached to the property. It should then calculate each country's tax independently before applying Article 8 marital relief and Article 9 credits. The U.S. $60,000 NRNC threshold should never be substituted for a treaty unified-credit computation.

Frequently Asked Questions (6)