Americans Living in the UK - Part 4: Treaty, Reliefs & Credits

After having discussed retirement and estate planning in part 3 of our series on Americans Living in the UK, we now turn to one of the most technical parts of the cross-border picture: the treaty, foreign tax reliefs and tax credits. For Americans living in the UK, avoiding double taxation is not simply a matter of knowing that a treaty exists. It requires an understanding of how the UK/US income tax treaty interacts with domestic tax rules in both countries, when foreign tax credits are available, and which forms and disclosures may be needed to support a claim. This article is written from a UK perspective and gives general guidance only. Detailed US tax advice should be taken separately.

The technical rules that actually stop Americans in the UK being taxed twice

For Americans in the UK, the tax treaty is important, but it is also widely misunderstood. It does not wipe away US filing obligations, and it does not magically decide every cross-border tax issue for you. What it really does is allocate taxing rights, set withholding limits for certain income streams, provide tie-breaker rules for dual residence cases, and help both countries give credit or relief where the same income is taxed twice.

The first thing to understand is the treaty’s saving clause. Under Article 1, the United States can generally continue to tax its residents and, crucially, its citizens, as if the treaty had not come into effect, subject to specific exceptions. That is why a US citizen living in London will usually still file a US return even where the treaty clearly gives the UK primary taxing rights over an item of income. In other words, the treaty helps, but it does not let most Americans simply opt out of the IRS.

That same point explains why the treaty is often most useful indirectly. Rather than eliminating all US tax, it often helps you claim a better foreign tax credit result, or stops the wrong country from withholding too much tax at source. Article 24 is central here because it requires double tax relief, but subject to the limitations of domestic law, so treaty relief and domestic credit rules work together, not separately.

What the treaty covers, and what it does not

The income tax treaty applies to taxes on income and capital gains. On the US side it covers federal income taxes, but excludes social security taxes. On the UK side it covers income tax, capital gains tax, corporation tax, and petroleum revenue tax. That scope matters because many cross-border headaches sit outside it.

So what is outside the treaty? First, US state taxes are a separate problem. Some US states do not honour treaty provisions. Second, social security and National Insurance coordination is handled under a separate US-UK totalisation agreement, not the income tax treaty. Third, reporting systems such as FBAR and FATCA Form 8938 arise under separate legal regimes, so treaty relief does not switch those off. As a practical matter, you can have a perfect treaty position on income tax and still have separate reporting obligations.

A second major misconception is that the treaty contains every cross-border death tax answer. It does not. Estate and inheritance issues often fall under a different treaty track from the income tax one. So if you are dealing with US estate tax and UK inheritance tax, you may need to look beyond the income tax treaty.

Dual residence, where treaty residence really matters

Some Americans in the UK are resident under both countries’ domestic rules at the same time. In those cases, the treaty’s tie-breaker rules matter. The classic sequence is permanent home, then centre of vital interests, then habitual abode, then nationality, and if needed the competent authorities can try to resolve the case. Once one test settles the issue, you do not keep moving down the list.

But treaty residence is not the same as escaping UK or US compliance entirely. Even if the tie-breaker allocates treaty residence to the other country, a person can still remain UK resident for domestic law purposes and still have to complete UK returns and comply with filing rules. On the US side, the saving clause means a US citizen cannot usually use treaty residence alone to stop US taxation. This is one of the most technical areas in the entire cross-border space, and one of the easiest to overstate.

The treaty articles most individuals actually use

Dividends

Article 10 says dividends may be taxed in the shareholder’s residence state, but the source state may also tax them, subject to limits. In the standard case, the treaty caps source-country withholding at 15 percent. There is a 5 percent rate for certain corporate shareholders with at least 10 percent voting ownership, and possible 0 percent outcomes in some narrow cases, including certain large corporate holdings and some pension scheme cases. For most individual investors, the practical figure to remember is the 15 percent treaty rate, not the full domestic non-treaty withholding rate.

Interest

Article 11 is more generous. Interest arising in one state and beneficially owned by a resident of the other state is generally taxable only in the residence state, unless the permanent establishment or special relationship rules apply. In plain English, ordinary cross-border bank or bond interest is often not supposed to suffer source-country tax under the treaty at all.

Royalties

Article 12 uses a similar approach. Royalties arising in one state and beneficially owned by a resident of the other are generally taxable only in the residence state, again subject to carve-outs such as permanent establishment cases and special relationship rules. That is why royalty income is one of the clearest examples where treaty wording can materially reduce source-country withholding.

Pensions, annuities and social security

This is where many Americans in the UK get tripped up. Article 17 says ordinary pensions and similar remuneration are generally taxable only in the recipient’s state of residence. But lump-sum payments from a pension scheme are treated differently. They are generally taxable only in the state where the pension scheme is established. The same article also says social security payments made by one state to a resident of the other are generally taxable only in the recipient’s residence state, and annuities are also generally taxable only in the recipient’s residence state. These distinctions matter a great deal when you move from ongoing pension income to one-off drawdown or lump sums.

Article 18 then deals with pension schemes themselves. It says that where an individual resident in one state participates in a pension scheme established in the other, income earned by the pension scheme may generally be taxed as that individual’s income only when paid out to that person, subject to Article 17. It also contains rules that can preserve cross-border tax relief for contributions and employer contributions in some work-move situations. That is one reason pension articles need to be read together, not one by one.

Limitation on benefits, less scary for individuals than for entities

The treaty contains a Limitation on Benefits article, which is anti-treaty-shopping language. For companies, funds and other structures, this can get technical fast. But for ordinary individuals, the news is usually simpler. Most individual Americans are not wrestling with the complex ownership and base-erosion tests that entities face. Advisers still need to watch this area for companies and investment structures, but it is rarely the main obstacle for a straightforward individual return.

How relief usually works in real life

On the US return

The standard US mechanism is the foreign tax credit. Individuals generally claim it on Form 1116. There is also an important point that often gets missed. If you exclude income under the foreign earned income exclusion or housing exclusion, you cannot also claim a credit for the foreign tax on the same excluded income. That is why the FEIE versus FTC choice is still a live strategic question for many Americans abroad.

A subtle but powerful treaty rule appears in Article 24. It says that for US credit purposes, gross income derived by a US resident that may be taxed in the UK under the treaty is treated as UK source income for applying the US credit rules. In practice, that re-sourcing rule can help where the normal domestic sourcing rules would otherwise make the foreign tax credit unusable or less efficient.

The credit is not unlimited. The foreign tax credit is limited by category and by the amount of US tax attributable to the foreign source income in that category. It is also important that only the amount of foreign tax that is actually creditable counts. If a treaty would have reduced the foreign tax, then only the treaty-reduced amount is creditable, and any excess may need to be reclaimed from the foreign country rather than credited on the US return.

This also matters after the year ends. If the foreign tax later changes, for example because of a refund, audit, repayment or redetermination, the US position may need to be corrected. Foreign tax credit carryovers, redeterminations and amended positions are a common source of cleanup work.

On the UK return

On the UK side, the core mechanism is double taxation relief or foreign tax credit relief. Relief can arise under a treaty or, in some cases, unilaterally. The key ceiling is simple. The UK credit is the lower of the foreign tax paid, or treaty-allowed amount, and the UK tax attributable to the same income or gain. Where a treaty caps foreign withholding, any excess beyond that cap is not available as UK credit.

A useful practical point is that UK credit is generally calculated item by item, not by lumping unlike amounts together. If there are multiple foreign dividends or gains, you will usually need separate calculations rather than one blended credit computation. That detail gets missed surprisingly often in self-prepared returns.

Which forms and documents matter most

For most Americans in the UK, the core US documents are Form 1116 for the foreign tax credit and, where a true treaty-based return position is being disclosed, Form 8833.

For US-source investment income, many Americans living in the UK also need to remember a basic paperwork point. W-9 is the form used to provide your correct taxpayer identification number to a payer required to file an information return with the IRS, whereas W-8BEN is for a foreign person claiming treaty-based withholding relief from a US withholding agent. For a US citizen with a US brokerage account, the default form is usually W-9, not W-8BEN.

On the UK side, the main compliance form is usually SA106 Foreign alongside the rest of the Self Assessment return. For people claiming relief from UK withholding while resident in another treaty country, HMRC also provides treaty claim forms, including forms specific to individuals under the UK-US convention.

When a foreign tax authority or withholding agent wants proof that you are a US resident for treaty purposes, the IRS has a separate certification process. That document can still be important in cross-border claims, even though many individuals do not need it every year.

Recent and upcoming changes to watch

The biggest UK background change is that the foreign income and gains regime replaced the remittance basis from 6 April 2025. That means UK residents are now generally taxed on the arising basis on worldwide income and gains, subject to the availability of relief for qualifying new residents. As a result, older remittance basis instincts need to be handled much more carefully in current UK-US planning.

There is also a practical compliance change from 6 April 2026. Making Tax Digital for Income Tax applies to sole traders and landlords with more than £50,000 of qualifying income. For Americans in the UK with rental income or self-employment income, that is not a treaty change, but it is very much a cross-border administration change because it affects how UK figures are generated and evidenced.

On the US side, the broad treaty framework remains the same, but foreign tax credit guidance and form instructions should still be checked each year. The technical detail continues to matter, especially where taxpayers assume that any foreign tax automatically qualifies for credit.

Finally, exchange-rate discipline matters more than many people expect. US tax returns must be expressed in US dollars, while UK returns are of course prepared in pounds sterling. Small foreign exchange inconsistencies can create messy treaty credit mismatches, especially where income, withholding tax and relief claims are being tracked across both systems.

Bottom line

The US-UK treaty is best thought of as a framework, not a shortcut. It tells you which country gets first taxing rights over certain income, caps or removes withholding in some cases, gives tie-breaker rules for dual residence, and supports the foreign tax credit systems on both sides. But for Americans in the UK, the actual result still depends on domestic law, the saving clause, the correct forms, and whether you claimed the right relief in the right country.

The treaty is important, but it is only one part of the answer. In practice, avoiding double tax usually comes down to getting three things right: understanding which country has primary taxing rights, claiming the right credit or relief, and keeping the paperwork consistent on both sides.