ISAs, Funds and the PFIC Problem: Investing as a US Person in the UK

The ISA illusion

An ISA is a creature of UK statute, and the IRS is not bound by it. To the US a cash ISA is a bank account and a stocks and shares ISA is a brokerage account: every dividend, every interest payment and every gain inside the wrapper lands on the US return as if the wrapper did not exist. Because HMRC charges nothing on it, there is no UK tax to credit — the US tax is simply an extra cost, converting Britain's favourite tax shelter into a US taxpayer's ongoing liability.

That alone would make ISAs merely unattractive. What makes stocks and shares ISAs actively dangerous for US persons is what they usually contain.

PFICs: the punitive default

Nearly every UK retail investment fund — unit trusts, OEICs, most UK- and EU-listed ETFs, and the funds inside a typical stocks and shares ISA — is a passive foreign investment company (PFIC) in US terms. Congress designed the PFIC regime in 1986 to make deferral through foreign funds not worth having, and it succeeded:

• Gains and certain distributions are thrown back across your holding period and taxed at the highest ordinary income rates for each year, with an interest charge stacked on top.
• Each fund generally requires its own annual Form 8621.
• The softer elections (qualified electing fund, mark-to-market) depend on fund cooperation or US-market listing that UK retail funds rarely provide, and work best when made at purchase — not years later.

A modest, diligently built ISA fund portfolio can therefore produce US tax and preparation costs out of all proportion to its returns. This is the single most common expensive surprise we see in US–UK work.

The mirror problem: US funds under UK rules

The trap is symmetrical. The UK's offshore funds regime divides non-UK funds into those with HMRC reporting fund status and those without. A UK resident disposing of a non-reporting fund pays tax on the gain as income — at income tax rates, with no CGT annual exempt amount — instead of capital gains treatment. Plenty of US mutual funds sit outside the reporting regime; meanwhile reporting funds require investors to pick up their share of undistributed income annually.

So the American who keeps investing through a US brokerage after moving to Britain has the same problem in reverse: home-country funds, foreign-country penalty. Whether a given holding is on HMRC's published reporting funds list is checkable, fund by fund — and worth checking before a disposal, not after.

The narrow middle ground

Holdings commonly considered workable for US persons in the UK — as a framework for advice, not a recommendation — share one property: neither rulebook classifies them as a hostile fund.

Access is its own obstacle: EU-derived documentation rules restrict UK platforms from selling US-listed ETFs to retail customers, some US brokers restrict UK-resident accounts, and FATCA makes some UK platforms decline US persons entirely. Pension wrappers change the analysis again — funds held inside a treaty-protected pension are generally insulated from both regimes, which is one reason pensions carry so much of the load in US–UK portfolios.

Reporting wraps around everything

Whatever you hold, the accounts themselves are reportable: ISAs and UK brokerage accounts count towards the FBAR threshold and, at higher levels, Form 8938. Reporting an account is cheap; the expensive part is only ever the contents.

Sequencing a clean-up

Existing PFICs or non-reporting funds are a pricing exercise: what does exiting cost this year, under both systems, against the compounding cost of staying? Timing around a move is often decisive — the same disposal can be cheap before UK residence and punitive after, or vice versa — which is why this review belongs inside move planning whenever a move is in prospect.