What Happens to Your 401(k) or IRA When You Move to the UK?

You spent a career building a 401(k) or anIRA. Then you accept a role in London, or follow family across the Atlantic,and a practical question surfaces almost immediately: what actually happens tothat account now? The reassuring part is that the account itself does not needto go anywhere. The part that catches people out is everything that quietlychanges around it.

This article is aimed at US citizens,green-card holders, and other US-connected people who hold a 401(k) ortraditional IRA and are moving to, or already living in, the United Kingdom. Itexplains how the account is treated once you are UK tax-resident, where the USand UK tax systems interact, and which decisions tend to cause problems if theyare made without cross-border advice.

Your account stays put - and that is usually a good thing

A 401(k) is tied to a US employer's plan; an IRA sits with a US custodian. Neither is portable to a UK pension, and there is no mechanism to fold either into a UK SIPP or workplace scheme. When you become UK-resident, the account remains exactly where it is: US-sited, invested in US-dollar assets, and still growing tax-deferred under US rules.

That immobility is often misread as a problem. In practice it is frequently an advantage. A US retirement account keeps you inside the US tax-deferred system, gives you continued access to US-domiciled investments, and avoids the punitive treatment that can apply when a US person reaches instead for ordinary UK retail funds. The account does not need rescuing. It needs understanding.

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How the US-UK treaty taxes your distributions

The US-UK Income Tax Treaty is the document that decides who taxes what. For pensions and similar remuneration, the general rule under Article 17 is that periodic distributions are taxable in the country where the recipient lives. For a UK resident drawing income from a 401(k) or IRA, that points to the UK as the primary taxing authority.

There is an important complication for Americans. The treaty contains a 'saving clause' that preserves the right of the United States to tax its own citizens and green-card holders broadly as if the treaty did not exist. So a US citizen living in the UK can find that both countries assert a right to tax the same distribution. This is not double taxation in practice, because the system is built to resolve it: foreign tax credits, and the treaty's re-sourcing rules, are designed so that tax paid in one country offsets tax owed in the other. The mechanics are intricate, and the order in which the two systems apply matters, which is precisely why this is an area for professional coordination rather than guesswork.

Lump sums are treated differently from regular income. A one-off, full withdrawal does not necessarily follow the same residence-based rule as a monthly drawdown, and the treaty's treatment of lump-sum pension payments has its own provisions and its own areas of dispute. The practical point is simple: a large single withdrawal taken shortly before or after a move can land in an unexpected place tax-wise, and is worth modelling before it happens.

The early-withdrawal penalty travels with the account

US retirement accounts carry a 10% additional tax on most distributions taken before age 59½, on top of ordinary income tax. Becoming UK-resident does not remove this penalty - it is a feature of the US account, not of where you live. A saver who cashes out a 401(k) to fund relocation costs, a deposit, or a gap in income can therefore face US income tax, the 10% penalty, and a UK tax charge on the same money, all at once.

This is the single most common and most costly error in this area. The educational point is not 'never withdraw'; it is that an early withdrawal around the time of a move is a decision with three sets of consequences, and the sequencing and timing deserve careful attention.

When new UK residents arrive: the four-year FIG window

The UK abolished the old non-domicile remittance basis from 6 April 2025 and replaced it with a residence-based regime. Under the new Foreign Income and Gains (FIG) rules, individuals who become UK-resident after a period of at least ten consecutive non-resident years can claim relief on foreign income and gains for their first four years of UK residence.

For someone moving from the US, this window can affect how - and whether - US retirement distributions are taxed in the UK during those early years. Whether the relief applies to a given distribution depends on the rules and on individual circumstances, and claiming it is an active choice with trade-offs. It is mentioned here because the first four years are exactly when many movers make irreversible decisions, and the FIG regime can change the calculus.

Reporting, currency, and the practical mechanics

What you report, and where

A 401(k) or IRA held with a US custodian is a US account, so it does not usually create the same foreign-account reporting obligations that a US person's UK accounts do. The reporting that matters runs the other way: once UK-resident, distributions may need to be reported to HMRC, and a US citizen continues to file a US return on worldwide income. Two systems, two returns, one coordinated position.

Currency

Your account pays in dollars; your life inthe UK is priced in pounds. The exchange rate at the moment of each conversion,how frequently you convert, and whether income is needed immediately or can betimed all affect what the distribution is ultimately worth. Currency is not aside issue in cross-border retirement income; it is one of the main variables.

Access to your account from a UK address

Some US custodians restrict or close accounts once the holder has a non-US address. This does not change the tax treatment, but it can affect where the account can live and how it can be managed. Anticipating it before the move is far easier than reacting to a closure letter afterwards.

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An illustrative example

Consider a hypothetical US citizen, age 48,who moves from Boston to London for a five-year posting, leaving behind a former-employer 401(k) and a traditional IRA. Tempted to 'tidy up', sheconsiders withdrawing the IRA to consolidate her finances. Looked at in isolation, the withdrawal seems administrative.

Viewed across both systems, the same step would trigger US income tax, the 10% early-withdrawal penalty because she is under 59½, and a potential UK charge - while also forfeiting decades of tax-deferred growth. Left in place and understood, the accounts simply continue, with her early UK years potentially shaped by the FIG regime and her later income planned around the treaty. This example is hypothetical and for illustration only.