What US Expats Should Know About UK Pension Tax Rules

Moving between the United States and the United Kingdom can make pension planning considerably more complicated. Retirement accounts that receive favourable treatment in one country may be classified or taxed differently in the other, while US citizens generally remain subject to US filing requirements even after becoming UK residents.

The UK-US Double Taxation Convention provides important protections, but it does not make every pension tax-free or remove every reporting obligation. The treatment can depend on the type of pension, whether a payment is periodic or taken as a lump sum, the individual’s tax residence and whether the person remains a US citizen or green card holder.

Understanding these distinctions before making contributions, transferring a pension or taking benefits can help prevent unexpected tax liabilities.

UK Tax Residence Is the Starting Point

The first question is whether the individual is resident in the UK for tax purposes.

UK residence is determined under the Statutory Residence Test, which considers factors including days spent in the UK, accommodation, work patterns and connections with the country.

Since 6 April 2025, UK residents have generally been taxed on their worldwide income and gains as they arise. The former remittance-basis system has been replaced by a residence-based regime. This means that a UK-resident US expat may need to report pension income received from both UK and American retirement arrangements.

Tax residence should be established for each UK tax year because a person’s position can change after moving, leaving or spending substantial periods in both countries.

The Four-Year Foreign Income and Gains Regime

Some new UK residents may qualify for relief under the Foreign Income and Gains regime, commonly known as the FIG regime.

The regime can apply during an individual’s first four UK-resident tax years following at least ten consecutive tax years of non-UK residence. Qualifying individuals may claim relief on selected foreign income and gains, and eligible foreign pension income can fall within the regime unless it is treated as disqualified income.

A FIG claim is not automatically beneficial. Claimants lose certain UK allowances, including their Personal Allowance and Capital Gains Tax annual exempt amount, for the relevant year. The relief must therefore be assessed against the value of the pension income and the individual’s wider tax position.

The FIG regime also does not remove US tax and reporting obligations. A US citizen claiming UK relief may still need to include the pension income on a US federal tax return.

How the UK Taxes Foreign Pension Income

A UK resident is generally taxable on foreign pension income, subject to any applicable treaty provision or specific relief.

Since 6 April 2017, the UK has generally taxed 100% of foreign pension income received by a UK resident rather than applying the former 10% deduction. This can include income from US employer plans and individual retirement arrangements.

The amount ultimately taxable will depend on the type of payment and the UK-US treaty. Regular pension income, one-off lump sums and US Social Security benefits can each receive different treatment.

Why the UK-US Tax Treaty Matters

The UK-US Double Taxation Convention allocates taxing rights between the two countries.

Under Article 17, regular private pension income beneficially owned by a resident of one country is generally taxable only in that country. A UK resident receiving periodic distributions from a US pension would therefore ordinarily expect the UK to have the primary taxing right.

However, the treaty contains a US “saving clause”. This allows the United States to continue taxing its citizens under US domestic law as though much of the treaty did not exist. As a result, a US citizen living in the UK may still have to report and potentially pay US tax on pension income even where Article 17 assigns the ordinary taxing right to the UK.

Relief from double taxation may then be available through foreign tax credits, but the calculation and sourcing rules can be complex.

Periodic Payments from 401(k) Plans and Traditional IRAs

Regular withdrawals from a US 401(k), traditional IRA or similar retirement arrangement will generally be treated as pension income.

For a UK treaty resident, periodic pension payments are normally taxable in the UK under Article 17. The income may be added to the person’s other taxable income and charged at the applicable UK Income Tax rate.

A US citizen must generally continue reporting worldwide income to the Internal Revenue Service. This means the same distribution may also appear on the individual’s US tax return, although double-tax relief may prevent or reduce a second economic charge.

Care is required when converting payments into sterling because the UK tax calculation must use an appropriate exchange rate. Currency movements can create differences between the taxable amounts reported in each country.

Roth IRA Distributions

Roth IRAs require separate analysis because qualifying distributions are generally exempt from US federal income tax.

Article 17 provides that pension income paid from a scheme established in the other country may remain exempt in the country of residence where the payment would have been exempt had the recipient remained resident in the country where the scheme was established.

This provision can protect qualifying Roth IRA distributions from UK tax, provided the arrangement and withdrawal satisfy the relevant treaty and US qualification requirements.

Actions taken after becoming UK resident can complicate the position. Additional contributions, conversions or changes to the arrangement should therefore be reviewed before they are made rather than assuming that every Roth withdrawal will automatically receive treaty protection.

Pension Lump Sums Are Treated Differently

One of the most important distinctions under the treaty is the difference between periodic pension income and a lump-sum payment.

Article 17 states that a lump sum derived from a pension scheme established in one country and received by a resident of the other country is generally taxable only in the country where the pension scheme was established.

For example, a genuine lump sum from a US pension received by a UK treaty resident may fall within the taxing rights of the United States rather than the United Kingdom.

The classification of the payment is critical. A complete withdrawal may qualify as a lump sum, while a series of withdrawals may be treated as periodic pension payments. The tax result should not be assumed solely because a provider describes a withdrawal as a “distribution”.

The US saving clause may also affect US citizens receiving lump sums from UK pension schemes, potentially allowing the United States to impose tax despite the treaty’s general allocation of taxing rights. Double-tax relief may then need to be considered.

The UK Tax-Free Pension Lump Sum Does Not Automatically Translate to the US

UK pension rules may allow part of a qualifying UK pension to be taken without UK Income Tax, subject to the applicable lump-sum limits and scheme rules.

A US taxpayer should not assume that the same amount will also be tax-free in the United States.

US tax law may calculate the taxable portion of a UK pension distribution differently. The result can depend on matters such as employee contributions, employer contributions, the individual’s cost basis and treaty protection.

Taking a UK pension commencement lump sum without first checking the US treatment can therefore create an unexpected US liability.

US Social Security Benefits

US Social Security payments are treated differently from private pensions.

Article 17 provides that payments made under the social security legislation of one country to a resident of the other are taxable only in the recipient’s country of residence. This provision is preserved from the US saving clause.

A US citizen who is treaty-resident in the UK may therefore find that US Social Security is taxable in the UK rather than the United States.

The UK tax calculation may differ from the way Social Security would have been taxed had the individual remained resident in America, so the amount received should be reviewed as part of the person’s overall UK income position.

Government Service Pensions

Pensions arising from government employment may be governed by Article 19 rather than the standard private-pension provisions.

The treaty generally assigns taxing rights over a government service pension to the country paying it. An exception may apply where the recipient is both resident in and a national of the other country.

US federal, state or local government pensions should therefore be identified separately from private-sector retirement benefits.

The individual’s citizenship and the nature of the former employer can materially change the outcome.

Contributing to a UK Pension as a US Citizen

US expats working in the UK may participate in workplace pensions, personal pensions or self-invested personal pensions.

UK tax relief may be available on qualifying contributions, subject to earnings-related limits, the annual allowance and other pension rules.

The treaty also contains provisions that may allow a US citizen working in the UK to receive corresponding US tax treatment for certain contributions to and benefits accrued within a qualifying UK pension scheme. The relief is subject to detailed conditions and cannot exceed the relief that would have applied to a generally corresponding US pension arrangement.

This protection does not mean that every UK pension or every personal contribution is automatically deductible on a US return. The type of scheme, employment relationship and contribution level must be considered.

Continuing Contributions to a US Retirement Plan

A person who moves to the UK may wish to continue contributing to an existing IRA or employer-sponsored US plan.

Eligibility under US rules does not necessarily mean that the contribution will qualify for UK tax relief.

The UK may not recognise a contribution to a US retirement plan in the same way that it recognises a payment into a UK-registered pension. Treaty relief can sometimes apply where an individual was already participating in the US plan before beginning employment or self-employment in the UK, but specific conditions must be met.

Contributions should be reviewed from both sides before payment, particularly where the individual expects tax relief in both jurisdictions.

Transferring Pensions Between the UK and US

Direct pension transfers between the two countries are rarely straightforward.

A US retirement plan may not accept a transfer from a UK pension, while an American scheme may not meet the requirements needed to receive a tax-advantaged UK pension transfer.

An attempted transfer can trigger UK tax charges, US tax consequences or both. The transfer may also affect future treaty treatment and reporting.

For many US expats, retaining separate UK and US retirement arrangements may be more practical than attempting to consolidate them, although this depends on the person’s circumstances, investment objectives and future residence plans.

Foreign Tax Credits and Double-Tax Relief

Where both countries tax the same pension income, foreign tax credits may be available.

The UK generally allows credit for qualifying foreign tax paid where the income is also taxable in the UK, subject to the treaty and UK limitations. The credit is normally restricted to the lower of the eligible foreign tax and the UK tax attributable to that income.

US foreign tax credits may similarly reduce US federal tax on income that has been taxed in the UK. The treaty contains additional rules intended to coordinate relief where the United States taxes a UK resident because that person is also a US citizen.

Credits do not always produce a complete offset. Differences in tax years, income sourcing, currency conversion and tax rates can leave residual tax in one country or create credits that cannot be used immediately.

US Reporting Continues After Moving to the UK

US citizens and resident aliens generally remain subject to US federal filing requirements on worldwide income, even while living abroad.

An interest in a UK pension or foreign deferred-compensation plan may also need to be reported on Form 8938 where the individual’s total specified foreign financial assets exceed the applicable threshold. The IRS specifically identifies foreign pension interests as potentially reportable assets.

Separate FBAR obligations may also arise where the individual has reportable foreign financial accounts and the aggregate value exceeds the filing threshold. Whether a particular pension arrangement constitutes a reportable financial account should be checked according to its legal and administrative structure.

Certain qualifying tax-favoured foreign retirement trusts may be exempt from Forms 3520 and 3520-A under Revenue Procedure 2020-17, but the exemption is conditional and does not eliminate other US reporting requirements.

The Timing of Pension Withdrawals Matters

The tax result can change depending on whether benefits are taken before or after becoming UK resident.

A withdrawal made while solely US resident may receive different treatment from one taken after UK treaty residence begins. The difference can be particularly significant for large lump sums, Roth accounts and distributions intended to fund a move to Britain.

Individuals planning to relocate should model the tax consequences before establishing UK residence rather than waiting until a withdrawal has already been processed.

The UK and US tax years also operate on different dates. The UK tax year runs from 6 April to 5 April, while the US generally uses the calendar year. A single pension payment may therefore be reported in different tax periods in each country.

Common Pension Tax Mistakes

Problems often arise when US expats assume that:

• a payment described as tax-free in one country must also be tax-free in the other;

• the treaty removes the requirement to file a US tax return;

• every withdrawal from a pension is treated as a lump sum;

• UK pension contributions automatically receive US tax relief;

• foreign tax credits will always cancel the entire second tax charge;

• pension accounts do not need to be included in US information reporting.

Each assumption can be wrong depending on the pension arrangement and the individual’s circumstances.

Planning Before Taking Pension Benefits

Cross-border pension planning should ideally take place before a contribution, conversion, transfer or withdrawal is made.

The review should establish the individual’s UK and treaty residence, US citizenship or green-card status, pension type, contribution history and intended form of withdrawal.

It should also consider whether the individual qualifies for the FIG regime, whether the payment is periodic or a genuine lump sum, which country has the primary taxing right and how double-tax relief will be claimed.

For US expats, pension decisions cannot be viewed through either the UK or US system in isolation. Coordinating both tax regimes before accessing retirement savings can protect treaty benefits, reduce reporting errors and prevent an apparently routine pension decision from creating an avoidable cross-border tax liability.