UK-US double tax treaty 101

If you are a US citizen who has moved, or is about to move, to the United Kingdom, you are about to join a small group of people who are fully taxable in two countries at once.

The reason is a quirk of American law. The United States taxes on citizenship. The United Kingdom taxes on residence. Almost every other country uses residence alone. The US is the outlier.

So the moment you become UK tax resident, two tax systems reach for the same income at the same time. The UK wants tax on your worldwide income because you live here. The US wants tax on your worldwide income because of the passport in your drawer. Your salary, your Vanguard dividends, your Chicago rental, your 401(k), all of it sits in the crosshairs of both HMRC and the IRS.

The double tax treaty is what stops that becoming a 70% tax bill. But it works in a way that surprises most people, and it does not work automatically. This guide walks through exactly how the treaty carves up each type of income, with worked examples throughout.

What the treaty actually does

The current agreement is the 2001 UK-USA Double Taxation Convention, amended by a protocol signed in 2002 and in force since 31 March 2003. It has applied to UK income tax and capital gains tax since 6 April 2003, and to US federal income taxes since 1 January 2004.

The treaty does not decide whether you pay tax. It decides who gets paid first. For each category of income it assigns a primary taxing right to one country, then obliges the other to give a credit for the tax paid in the first. You generally end up paying the higher of the two rates, but only once.

A crucial threshold point. Under Article 4(2), a US citizen is only treated as a US resident for treaty purposes if they have a substantial presence, permanent home or habitual abode in the United States. If you have genuinely relocated to Britain, you are a UK resident for treaty purposes. That matters, because most of the allocation rules are written from the perspective of the residence State, and that is now the UK.

The savings clause

This is where most people’s understanding falls over.

Read Article 11 and you will see that interest is taxable only in your country of residence. Read Article 13(5) and share gains are taxable only in your country of residence. Read Article 17(1) and pensions are taxable only in your country of residence.

Then read Article 1(4), the savings clause:

Notwithstanding any provision of this Convention except paragraph 5 of this Article, a Contracting State may tax its residents, and by reason of citizenship may tax its citizens, as if this Convention had not come into effect.

In plain English, the US reserves the right to ignore the treaty entirely when taxing its own citizens. Every taxable only in the UK provision is, for you, quietly rewritten as taxable in the UK, and also in the US anyway.

This is the single most important thing to understand about the treaty, and it is why the mechanics run in a particular direction.

Image 1 — how the savings clause works in practice

That credit mechanism sits in Article 24(6). It is elegant once you see it. Because a US citizen would normally have no foreign tax credit available against US tax on US-source income, Article 24(6)(d) deems that income to arise in the UK, purely for the purpose of relieving double taxation, so that UK tax can be credited against it on Form 1116.

There are a handful of provisions the savings clause cannot touch. Article 1(5) lists them, and they are worth knowing, because they are where the genuine planning opportunities live.

●       Article 17(1)(b). Pension payments exempt in the source country stay exempt in the other.

●       Article 17(3). Social security is taxable only in the country of residence.

●       Articles 18(1) and 18(5). Pension scheme growth, and relief for UK pension contributions.

●       Articles 24, 25 and 26. Double tax relief, non-discrimination and mutual agreement.

Everything else is fair game for the IRS.

Quick reference: who taxes what

Rates used in the examples below are illustrative and based on 2026/27 UK figures. Always check current rates and thresholds before relying on any calculation.

Employment income

Article 14. Employment income is taxable where the work is physically performed. As a UK resident your UK workdays are UK-taxable, and because you are a US citizen they are US-taxable too.

The split matters most if you work for a US employer. Article 14(2) only exempts short-term visitors whose remuneration is paid by an employer who is not resident in the country where the work is done. If your employer is a US company, that exemption fails for your US workdays, and the US retains the primary right to tax them.

●       US workdays with a US employer: the US taxes first, the UK gives the credit.

●       All other workdays: the UK taxes first, the US gives the credit.

Example: Michael, £160,000 salary, US employer

Michael lives in London and works for a US corporation. Of his 220 working days, 22, or 10%, are spent on business trips to New York.

●       UK.  Taxes the full £160,000 as a UK resident, giving tax of roughly £58,200.

●       US workdays.  £16,000 is US-source and the US may tax it under Article 14 regardless of citizenship. US tax on that slice at 35% is about £5,600. The UK must give credit for it, dropping the UK bill to roughly £52,600.

●       UK workdays.  The remaining £144,000 is taxed by the US only because Michael is a citizen. Article 24(6) re-sources it to the UK, so the UK tax on that slice, comfortably more than the US tax, wipes out the US liability on Form 1116.

Net result: Michael pays UK rates overall, with excess foreign tax credits carried forward. He does not pay 76%.

Two things worth flagging. First, the Foreign Earned Income Exclusion on Form 2555 is a domestic US relief, not a treaty relief, and in a high-tax country like the UK the foreign tax credit is usually the better choice, because it generates carryforwards the exclusion does not. Second, Article 18(5) lets a US citizen employed in the UK deduct their UK workplace pension contributions on their US return, and excludes employer contributions from US income. This is protected from the savings clause and is routinely missed.

Bank interest

Article 11(1) says interest is taxable only in the country of residence, meaning the UK. In principle, no US tax. In practice the savings clause means the US taxes it anyway, and then gives the credit.

Example: Emily, $20,000 of US bank interest

●       UK.  Taxes the whole amount at her marginal rate of 40%, less the personal savings allowance. Roughly $7,800.

●       US.  Taxes it at 32%, about $6,400, but Article 24(6) treats it as UK-source, so the UK tax fully covers it. US liability nil.

Net result: $7,800, all to HMRC.

Dividends

Article 10(2)(b) gives the source country the right to tax portfolio dividends, capped at 15%. So for dividends from US companies, the US gets the first 15% and the UK credits it.

In practice no US withholding actually occurs, because your broker does not withhold on a US person. But 15% is still the amount the US is entitled to under the treaty, and it is the amount the UK will credit.

Example: James, $50,000 of US dividends

●       US.  Entitled to 15% under the treaty, being $7,500.

●       UK.  Taxes at the higher dividend rate of 35.75%, being $17,875, and gives credit for the $7,500, leaving $10,375 payable to HMRC.

●       US tax above 15%.  Relieved via Article 24(6), with the excess UK tax credited on Form 1116.

Net result: $17,875 in total, at the UK rate, split between two treasuries.

Rental income

Article 6 gives the country where the property sits the primary taxing right. Most Americans moving to the UK keep a property back home, so US property means the US taxes first and the UK gives the credit, while UK property runs the other way.

The complication is not the treaty. It is that the two countries compute rental profit very differently, so the credit rarely lines up cleanly.

Example: Dana, a Boston condo

Dana nets $24,000 a year from her Boston rental.

●       US.  She claims depreciation of around $12,000, cutting taxable profit to $12,000. US tax at 24% is $2,880.

●       UK.  HMRC gives no depreciation relief, and restricts mortgage interest to a 20% basic rate tax reducer. UK taxable profit is closer to $30,000, taxed at 40%, so about $12,000, less credit for the $2,880 of US tax, leaving $9,120.

Net result: roughly $12,000 in total, and the credit only absorbs a quarter of the UK bill.

Private pensions: regular payments

Article 17(1)(a) makes pensions taxable only in the country of residence, meaning the UK. The savings clause lets the US tax anyway, and the US gives the credit.

Example: Robert, $40,000 a year from his 401(k)

●       UK.  Taxes the full $40,000 as pension income, roughly $12,000 at his marginal rate.

●       US.  Taxes it too, but Article 24(6) re-sources it and the UK tax more than covers the US liability. US tax nil.

Net result: UK rates. Robert should file a Form W-4P with his plan administrator to reduce US withholding, or he will be lending the IRS money for a year.

A genuinely valuable point concerns Roth IRA distributions. Under Article 17(1)(b), which the savings clause cannot override, a payment from a US pension scheme that would be exempt in the US if the recipient lived there is exempt in the UK as well. Roth IRAs are named as pension schemes in the exchange of notes to the treaty. A qualified Roth distribution should therefore be tax-free in both countries, which makes Roth conversions before departure worth serious thought.

The reverse also holds. A US citizen with a UK pension taking the 25% tax-free pension commencement lump sum can generally rely on Article 17(1)(b) to keep it exempt in the US too.

Private pensions: lump sums

Article 17(2) carves lump sums out of the general rule. A lump-sum payment from a pension scheme established in one country and owned by a resident of the other is taxable only in the country where the scheme sits. For a 401(k) or IRA that means the US has the primary right, and the UK gives the credit.

Example: Robert takes a $200,000 lump sum

●       US.  Taxes it at 32%, being $64,000. Add a 10% early distribution penalty if he is under 59 and a half.

●       UK.  Taxes it too, at 45%, being $90,000, but gives credit for the $64,000 of US tax, leaving $26,000 for HMRC.

Net result: $90,000 in total. The UK rate wins.

⚠️ WARNING  HMRC’s view is that Article 17(2) applies to a genuine lump sum, meaning a full commutation of the entire pension entitlement, and not to partial drawdown withdrawals, which it treats as ordinary pension income under Article 17(1). The distinction changes which country taxes first and is one of the most contested areas of the treaty. Take advice before drawing anything.

US social security

This is the one place the treaty gives an unambiguously clean answer.

Article 17(3) provides that social security payments made by one country to a resident of the other are taxable only in the country of residence. Critically, Article 17(3) is listed in Article 1(5)(a), so the savings clause does not apply. The US does not tax your social security at all. Only the UK does.

Example: Linda, $36,000 of US social security

●       UK.  Taxes it as pension income at her marginal rate, roughly $9,500.

●       US.  No tax. She reports the SSA-1099 and claims the treaty exemption, disclosing the position on Form 8833.

Note that this is not always good news. The US would have taxed at most 85% of the benefit, whereas the UK taxes all of it. For someone whose social security is their main income, the UK bill can exceed what they would have paid at home.

Government service pensions

Article 19(2) handles pensions for government service, covering federal, state, local and military. The answer turns entirely on nationality. If you are a US citizen only, the pension is taxable only in the US and the UK exempts it. If you are also a British national and UK resident, it becomes taxable in the UK.

Example A: Frank, US citizen only, $50,000 federal pension

Article 19(2)(a) gives the US exclusive taxing rights. The UK does not tax it, and Frank claims the treaty exemption on his self assessment return. US tax is about $11,000 at 22%, and UK tax is nil.

Example B: Frank naturalises as a British citizen

Article 19(2)(b) flips the primary right to the UK, because he is now resident and a national there. UK tax is about $20,000 at 40%. The US still taxes under the savings clause, since Article 19 is only protected for people who are not citizens of the taxing state, but gives credit for the UK tax, reducing the US bill to nil.

Net result: taking British citizenship nearly doubles Frank’s tax on his federal pension.

That is not a reason to avoid naturalising. It is a reason to model the cost before filing the application. The same asymmetry applies to indefinite leave to remain, which can affect whether the UK is obliged to honour the Article 19 exemption at all.

Gains on shares and funds

Article 13(5) makes gains on everything other than real property taxable only in the country of residence. The UK taxes, the savings clause lets the US tax too, and the US gives the credit.

Example: Priya sells $100,000 of stock

●       UK.  Capital gains tax at 24%, less the annual exempt amount, so roughly $24,000.

●       US.  Long-term capital gains at 20% plus 3.8% net investment income tax, about $23,800. The 20% + 3.8% is covered by credit for the UK tax.

Net result: $24,000, which is equally what you would have paid regardless of where you live.

Gains on property

Article 13(1) gives the country where the property sits the right to tax the gain. For your US home or rental that is the US, and the UK gives the credit.

Example: Tom sells his Chicago rental, $300,000 gain

●       US.  $60,000 of depreciation recapture at 25%, being $15,000, plus $240,000 at the 20% long-term rate, being $48,000, plus 3.8% net investment income tax of $11,400. About $74,400 in total.

●       UK.  Capital gains tax is computed in sterling, using the exchange rates at purchase and at sale. If the dollar strengthened over Tom’s ownership period, the sterling gain is larger than the dollar gain, say the equivalent of $360,000. At 24% that is $86,400, less credit for the $74,400 of US tax, leaving about $12,000 for HMRC.

Net result: roughly $86,400, and around $12,000 of it exists purely because of currency movement.

Currency is the recurring villain here. So is the mismatch between the US section 121 exclusion, at $250,000 or $500,000 on a main home, and UK private residence relief. A former US main home can be fully exempt in the US and fully taxable in the UK, leaving no US tax to credit.

The first four years: the FIG regime

One development changes the picture substantially for new arrivals. The UK abolished the remittance basis and non-dom status from 6 April 2025, replacing them with the foreign income and gains regime.

If you have not been UK tax resident in any of the previous ten tax years, you can claim full relief on foreign income and gains for your first four years of UK residence. For an American, foreign means non-UK, so your US dividends, US interest, US rental income and US capital gains can fall outside UK tax entirely for four years.

That sounds like an unambiguous win, and it often is. But note the consequences.

●       Claiming the relief means losing your personal allowance and capital gains annual exempt amount for that year.

●       With no UK tax paid on that income there is no foreign tax credit, so the US tax applies in full and you build no carryforwards.

●       The income must still be reported, and the claim made correctly, or the relief is lost.

For a US citizen the four-year window is often the single best planning opportunity of the whole move. It is a period in which realising US gains, converting to a Roth, or taking pension distributions may be taxed once at US rates rather than twice with credits in between. It closes permanently at the end of year four.

Read the treaty before you plan

Every scenario above turns on the wording of a specific article. Whether your pension withdrawal is a lump-sum payment, whether your employer is a resident of the other State, whether you are a national of the UK. These are not academic distinctions. They determine which country taxes first, which credit you can claim, and in the case of social security and government pensions, whether one country taxes you at all.

The treaty is a public document, it is not long, and it is written more clearly than most tax legislation. Anyone planning a move across the Atlantic should read it, particularly Articles 1, 4, 14, 17, 19 and 24.

●       HMRC, full consolidated text: the 2001 UK-USA Double Taxation Convention as amended by the 2002 protocol.

●       HMRC, all UK-USA treaty documents.

●       IRS, treaty, protocol and technical explanation.

The technical explanation published by the US Treasury is particularly useful. It explains the intended operation of each article, including the savings clause and the Article 24(6) credit mechanism, in far more detail than the treaty text itself.

Getting both sides right

The recurring failure in transatlantic tax is not that people ignore the treaty. It is that they get advice on one side of the Atlantic only. A UK adviser who does not know how Form 1116 baskets work, or a US preparer who does not know how the FIG regime interacts with foreign tax credits, will each produce a defensible return, and between them lose you thousands.

The two returns have to be planned together, in the right order, with the credits modelled before the transactions happen rather than after.

We handle the UK side. For the US side we work with Bright!Tax, a US expat tax practice serving Americans across many countries.

Between us, both returns get prepared by people who understand what the other one is doing.