UK to US Financial Planning: Five Common Mistakes

Most people relocating to the US focus their attention on logistics - visas, housing, schooling - and assume their financial affairs can be sorted out once they have settled in. When it comes to UK investments, this is a costly assumption.

The fundamental problem is that the US and UK tax systems view investment wrappers and asset types very differently. A structure that is highly efficient in the UK may be treated in a completely different way - and sometimes punitively - once you become a US tax resident. The IRS taxes US residents on their worldwide income and does not automatically recognise the tax-advantaged status of UK investment accounts. But the issue goes further than any single account type.

Before relocating, it is worth reviewing your entire UK investment portfolio through a US tax lens. This means considering not just what you hold, but where it is held, how it is structured, and what the US tax treatment of each element will be after your move. UK-domiciled funds, certain investment bonds, ISAs, and assets held in wrappers that have no US equivalent can all create unexpected liabilities if carried across unreviewed.

There is also a significant opportunity in this process that is easily missed. While you remain a UK resident, you may be able to crystallise gains in a more tax-efficient way than would be possible after you move, taking advantage of UK allowances before your residency status changes. Once you are subject to the US tax system, the options available to you narrow considerably. Acting before departure gives you the flexibility to reposition your portfolio on your own terms rather than being forced to do so reactively.

The practical goal is to arrive in the US with an investment portfolio that is structured for where you are going, not where you have been - one that will grow efficiently within the US tax framework rather than creating a compliance burden or eroding returns through avoidable tax charges. A qualified cross-border adviser can review your holdings, identify what needs to change, and help you time any disposals or restructuring to minimise the overall tax cost of the transition.

This is not a review that can be done effectively after the fact. By the time you are a US tax resident, some of the most valuable planning options will already be unavailable to you.

UK pensions represent one of the most complex areas of cross-border financial planning, and one of the most frequently mishandled. The instinct for many people is to try to consolidate their financial life - to transfer everything to the US and start fresh. When it comes to pensions, this can end up being an expensive mistake.

Transferring a UK pension directly to a US retirement account is rarely straightforward and is often impossible without triggering significant tax consequences. In most cases, such a transfer is treated as a taxable distribution in the United States, potentially resulting in a large income tax bill at the point of transfer. In many scenarios, the most tax-efficient course of action is simply to leave the UK pension where it is.

UK pensions, including SIPPs and occupational schemes, remain tax-deferred regardless of where you live. They also offer considerable flexibility in how and when you draw income - a flexibility that is notably absent from the US system, which imposes Required Minimum Distributions (RMDs) from accounts such as IRAs and 401(k)s once you reach a certain age.

There is, however, one action that is well worth considering before you depart: taking your 25% tax-free lump sum. Under current UK rules, pension holders can access a quarter of their pot as a tax-free cash payment from the age of 55 (from April 2028, this rises to age 57). This benefit does not follow you across the Atlantic - once you are a US tax resident, the tax-free status of this lump sum may not be recognised by the IRS. Taking it before you move can provide a useful cash reserve for early retirement years and reduce the complexity of managing cross-border pension income later.

The interaction between UK pension income and US RMDs requires a carefully coordinated withdrawal strategy. Without proper planning, you may find yourself drawing from both systems simultaneously in a way that pushes you into a higher tax bracket unnecessarily.

As you establish yourself in the United States, you will naturally begin building a financial footprint there - contributions to a 401(k) through your employer, if you work, perhaps an Individual Retirement Account (IRA), and various US-based savings and investments. Meanwhile, your UK assets - property, pensions, savings - continue to exist in a separate jurisdiction under a different regulatory and tax framework.

Over time, this creates what is often described as asset fragmentation: a situation in which your wealth is spread across two countries in a way that lacks coherence or coordination. Each element may be functioning reasonably well in isolation, but the portfolio as a whole is not being managed strategically.

The consequences of fragmentation become most apparent in retirement, when you begin drawing on your assets. A well-designed drawdown strategy considers the tax treatment of every income source, the sequencing of withdrawals, and the interaction between different accounts. When assets are fragmented across two jurisdictions, this kind of coordinated planning becomes extremely difficult. The result is often a higher overall tax burden than necessary, as income from different sources collides in ways that were not anticipated.

Fragmentation can also create significant complications for estate planning and the legacy you leave behind. The US is generally more generous than the UK when it comes to inheritance tax thresholds, which can make it advantageous to preserve and pass on US-based assets to the next generation. This means the sequencing of how you draw down your wealth during retirement is not just a tax efficiency question - it is also a legacy question. Drawing on your UK assets first, for example, may allow you to preserve assets in the more favourable US environment for your heirs. Without a coordinated view of your entire estate, these opportunities are easily missed. The decision about which pot to draw from, and when, has implications that extend well beyond your own retirement income.

The solution is to treat your assets as a single, integrated portfolio regardless of where they are held. This means working with an adviser who has visibility of your complete financial picture across both countries and can design a strategy that optimises your position holistically - both for the retirement you want to have and the legacy you want to leave.

The complexity of a UK-to-US move means that generalist financial advice is rarely sufficient. Many people continue working with their existing UK adviser during and after the transition, assuming that familiarity with their financial history compensates for any gaps in expertise. It does not.

UK advisers are typically not licensed to operate in the United States, and - through no fault of their own - may be unaware of the specific tax treatments and reporting obligations that apply once their client becomes a US resident. They may not flag issues with ISAS or be unfamiliar with the interaction between UK pension rules and US RMD requirements. They may have limited experience with the double taxation agreement and how to apply it in specific circumstances.

The cost of this gap in advice is not always immediately visible. Problems often emerge gradually: an unexpected tax bill here, a missed reporting obligation there. By the time the full picture becomes clear, unwinding the damage can be both technically complex and expensive.

Engaging a cross-border specialist - ideally one who is qualified in both the UK and the US and has direct experience of the interaction between the two systems - as early as possible in the planning process is one of the most important investments you can make. The goal is not simply compliance. It is building a financial strategy that is genuinely optimised for your life across both countries: one that protects your wealth, minimises unnecessary tax and remains aligned with your long-term objectives regardless of where you choose to live.