ISA vs Roth IRA for US Persons in the UK: What Actually Stays Tax-Free

For a US person living in the UK, the ISA and the Roth IRA are not interchangeable tax-free wrappers — they behave in almost opposite ways. The ISA is tax-free only in the UK: the IRS ignores the wrapper entirely, taxes everything inside it, and usually treats the funds held in a stocks-and-shares ISA as PFICs with punitive consequences. The Roth IRA generally works in both directions: tax-free in the US by design, and — on the position most cross-border practitioners take — respected by the UK under the US-UK tax treaty.

Key takeaways

An ISA is a UK-law wrapper with no US equivalent status. Interest, dividends and gains inside it are fully reportable and taxable on a US return.
Because the income is UK-tax-exempt, there is usually no UK tax to credit against the US tax on ISA income — the exemption works against you.
Stocks-and-shares ISAs holding UK or Irish funds typically create PFIC exposure, with Form 8621 reporting for each fund and a harsh default tax regime.
The Roth IRA is generally the better wrapper for a US person in the UK: tax-free in the US, and widely treated as protected under the US-UK income tax treaty — though the precise treaty treatment of Roth distributions should be confirmed for your facts.
An existing ISA problem is fixable. The worst response is to keep quiet; the usual routes are corrective reporting and, where returns missed it, the streamlined procedures.

This article is educational. We advise on the tax treatment of accounts and investments; we do not recommend investments, and nothing here is investment advice.

Why the ISA wrapper is invisible to the IRS

The ISA's tax-free status comes entirely from UK statute. US citizens and green card holders, however, are taxed by the US on worldwide income regardless of where they live — and the Internal Revenue Code contains no provision recognising the ISA. There is also no treaty article that exempts ISA income for a US person; the treaty's saving clause broadly preserves the US's right to tax its own citizens as if the treaty did not exist, with only limited exceptions (pensions among them — which matters for the Roth, below).

The practical result:

Cash ISA — the interest is taxable on your US return in the year it arises.
Stocks-and-shares ISA — dividends and realised gains are taxable on your US return, and the funds themselves usually raise the PFIC issue.
No offsetting credit — because the UK charges no tax on ISA income, there is generally no UK tax to claim as a foreign tax credit against the US liability. The UK exemption converts "tax-free" into "US-taxable with nothing to credit".

So when clients ask "are ISAs taxable in the US?", the honest answer is: yes, in full, every year — the wrapper simply does not exist in American eyes.

The PFIC trap inside stocks-and-shares ISAs

The deeper problem is what a UK stocks-and-shares ISA usually holds: OEICs, unit trusts, investment trusts and UK- or Ireland-domiciled ETFs. To the IRS these are foreign corporations earning passive income — which is the definition of a passive foreign investment company. We cover the mechanics fully in our guide to PFIC tax rules for US investors abroad; the short version is:

The default regime taxes gains and certain "excess distributions" as if earned rateably over your holding period, at the highest ordinary rates for each year, with an interest charge on the deemed late tax. Long holding periods make this brutal.
Each PFIC generally requires its own annual Form 8621 — an ISA holding a dozen funds can mean a dozen forms, every year.
The elections that soften the regime (QEF, mark-to-market) are often unavailable or unattractive for typical UK retail funds, and they work best when made from the start — not discovered years in.

None of this is altered by the ISA wrapper. A US person who opens a stocks-and-shares ISA on a UK platform's default fund list has, in most cases, unknowingly acquired a portfolio of PFICs.

The Roth IRA: the wrapper that usually survives both systems

The Roth IRA is the mirror image. Contributions are made from after-tax money; qualified distributions are tax-free under US law. And critically, the US-UK treaty — unusually generous on pensions — is widely read as protecting it on the UK side too.

The position most cross-border practitioners take is that the Roth IRA qualifies as a pension scheme for treaty purposes, so that a distribution which is exempt from US tax as a qualified Roth distribution is also relieved from UK tax under the treaty's pension article, and investment growth inside the account is not taxed by the UK as it arises. The pensions area is also one of the carve-outs from the saving clause, which is what lets a US citizen resident in the UK actually use it. The precise article-by-article treatment — including how HMRC characterises a particular distribution and what claims must be made on each return — should be confirmed for your circumstances before you rely on it. Treaty positions are claimed, not automatic, and a badly framed return can forfeit relief that was available.

Two practical cautions for expats:

Contribution eligibility is a US-law question. You need compensation the US recognises, within the Roth income limits — and income excluded under the foreign earned income exclusion does not count. Many US persons in the UK take foreign tax credits instead of the exclusion partly to preserve IRA eligibility.
A Roth is not a UK pension. It sits alongside, not instead of, UK workplace pensions and SIPPs, which raise their own cross-border questions — see our guide to US tax on UK pensions and SIPPs.

What HNW US persons in the UK typically do instead

Patterns we see among well-advised US persons in the UK — described factually, not as recommendations:

They avoid stocks-and-shares ISAs holding non-US funds, for the PFIC reasons above.
Some keep a cash ISA, accepting that the interest is US-taxable. It is a modest UK-side benefit with no reporting landmines — harmless rather than tax-free.
They fund US retirement wrappers first — Roth and traditional IRAs, and US employer plans where available — because these are the wrappers both systems respect.
For taxable investing, they generally hold US-domiciled ETFs or individual securities rather than UK/EU funds, avoiding PFIC status. One genuine friction: UK and EU PRIIPs rules require a key information document that most US-domiciled ETFs do not produce, so many UK retail platforms will not sell them. Access typically depends on the platform and the investor's classification; some use US brokerage accounts or platforms built for US persons abroad. This is a regulatory access issue to discuss with a platform or financial adviser — our role is the tax treatment either side of it.
They coordinate the two tax returns. The UK's own treatment of US accounts, remittance-basis history, and foreign tax credit ordering all interact — this is the core of our US-UK expat tax service.

Cleaning up an existing ISA problem

If you are a US person who has held a stocks-and-shares ISA for years, the sequence matters more than the speed:

1. Inventory the wrapper. Every fund, acquisition date and distribution history — PFIC analysis is holding-by-holding.

2. Establish what was reported. Were the dividends and gains on your US returns? Were Forms 8621 filed? Was the account captured on FBAR and Form 8938 where thresholds were met?

3. Do not sell reflexively. Disposals of PFICs are taxable events under the default regime; the order of elections, disposals and disclosures should be advised, not improvised.

4. Fix the history through the right door. Where past returns are wrong and the failure was non-wilful, the IRS streamlined procedures usually offer a penalty-protected route — our guide to streamlined filing for US expats explains eligibility and mechanics.

Most ISA problems we see were built innocently — a UK adviser or platform suggested the obvious UK product, unaware the client's US passport changed everything. The IRS's non-wilful routes exist for exactly this pattern, but they reward taxpayers who come forward before the IRS writes first.

Where we fit

ISA-versus-Roth questions sit precisely on the seam between the two systems, which is where DIY answers fail: the UK answer is right, the US answer is right, and the combined answer is wrong. At Next Tax Source this is private-client work — a licensed CPA or Enrolled Agent reviews and signs off every return and disclosure, and cross-border positions are documented, not assumed. If you hold an ISA as a US person, are weighing a Roth from the UK, or suspect past returns missed something, book a confidential consultation and we will map the exposure and the fix in plain English.

This article is general information, not tax or investment advice, and does not create a professional relationship. We advise on tax treatment only — we do not recommend investments or platforms. Treaty positions, thresholds and eligibility rules change and depend on individual facts; confirm the current position with a licensed professional before acting.

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Reviewed by a CPA / Enrolled Agent. Last updated: 4 September 2026.

Official sources: gov.uk — Individual Savings Accounts | IRS — About Form 8621 (PFIC) | IRS — United Kingdom Tax Treaty | IRS — International Taxpayers

Frequently asked questions

Are ISAs taxable in the US?+

Yes. The ISA is a UK tax wrapper only — the IRS does not recognise it. A US person must report interest, dividends and capital gains arising inside a cash or stocks-and-shares ISA on their US return each year, exactly as if the wrapper did not exist. The UK exemption removes UK tax on that income, but it does nothing on the US side, and it can leave you with US tax and no UK tax to credit against it.

Why do stocks-and-shares ISAs cause PFIC problems for US citizens?+

Most funds offered inside a UK stocks-and-shares ISA — OEICs, unit trusts, UK- and Ireland-domiciled ETFs — are non-US pooled investments, which the US tax code generally treats as passive foreign investment companies (PFICs). PFIC status brings a punitive default tax regime on gains and certain distributions, plus annual reporting on Form 8621 for each holding. The ISA wrapper does not change any of this, because the IRS looks straight through it to the underlying funds.

Is a Roth IRA tax-free in the UK?+

In broad terms, the position most practitioners take is that the US-UK income tax treaty respects the Roth IRA as a pension arrangement, so qualified Roth distributions that are tax-free in the US are also relieved from UK tax under the treaty's pension article. The precise treaty analysis depends on your facts, how the distribution is characterised, and correct treaty claims on both returns, so it should always be confirmed by a cross-border professional before you rely on it.

Can a US citizen living in the UK contribute to a Roth IRA?+

Only if the US-side conditions are met: you need US taxable compensation and income within the Roth eligibility limits. This is where the foreign earned income exclusion can backfire — income you exclude does not count as compensation for IRA purposes, so expats who exclude everything may have no capacity to contribute. Many instead use foreign tax credits rather than the exclusion, partly to preserve retirement-account eligibility. The interaction is fact-specific and worth professional review.

What should I do if I already hold a stocks-and-shares ISA as a US person?+

First, do not panic-sell — disposing of PFIC holdings has its own US tax consequences and sequencing matters. The right order is: inventory exactly what the ISA holds, establish what has and has not been reported to the IRS, then decide on elections, disposals and corrective filings with advice. If past US returns omitted the ISA income or Form 8621, the IRS streamlined filing compliance procedures often provide a penalty-protected route to fix the history for non-wilful taxpayers.

Should I just keep my ISA in cash instead?+

A cash ISA avoids the PFIC problem entirely, because bank interest is not a PFIC. But the interest is still fully taxable on your US return, so for a US person the cash ISA is merely harmless, not tax-free — you keep the UK exemption and simplicity while accepting US tax on the interest and, over the long term, the drag of holding cash. Whether that trade-off makes sense is a planning question, not a foregone conclusion.

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