UK pensions are one of the areas where the US-UK treaty does genuine work. Growth inside a recognised scheme is generally not taxed by the US as it accrues — the outcome most people would hope for, and not one you can take for granted with foreign retirement accounts generally.
But the protection is not automatic, it is not complete, and the places where it runs out are exactly where the expensive assumptions live.
What the treaty actually protects
Article 18(1) is one of the few treaty provisions listed as surviving the saving clause for citizens, which is why it works at all for a US passport holder. Properly claimed, it shelters growth inside employer schemes and SIPPs from annual US taxation.
Contributions are a different paragraph and a different answer. The relief for contributions sits in Article 18(2), and the saving clause carve-out for that one reaches only individuals who are not citizens of the taxing state — so a US citizen cannot lean on it against the IRS. Growth and contributions have to be argued separately, not as one package.
Claimed is the operative word: the position should be established on the return, consistently, rather than assumed. And the scheme still appears on the FBAR and often Form 8938 — treaty protection is about tax, not disclosure.
Contributions and the edges of protection
Employer contributions and personal contributions are looked at differently, and relief on the US side does not automatically mirror the UK's generous treatment. Large employer contributions in particular can raise current-tax questions the payslip never hints at.
SIPPs add a second layer: a self-invested pension holding UK retail funds raises PFIC questions inside the wrapper. The conservative reading keeps the treaty shelter over the whole structure, but fund choice inside a SIPP still deserves the same US-aware eye as any other account.
The lump sum, where real money gets lost
Twenty-five percent of a UK pension can typically be taken free of UK tax. That relief is a feature of UK law, not of the treaty, and the US does not simply follow it. Taking a lump sum while US-resident, without modelling it first, is one of the most expensive unforced errors in cross-border tax.
Timing relative to a move matters more than people expect: the same withdrawal can produce materially different outcomes depending on which side of a residence change it falls. Drawdown order across UK pensions, IRAs and 401(k)s is a genuine planning lever — which is an argument for sequencing the retirement, not just reacting to it.