You worked in the UK. You saved diligently. You did everything right. And now you are living in the United States, or thinking about making the move (see UK ISA Living in the USA: New Options for British Expats), and someone has mentioned that your ISA might not be the tax-free account you always thought it was.

They are right. And the details matter.

A UK Individual Savings Account is one of the most efficient savings tools available to UK residents. It shelters interest, dividends, and capital gains from UK income tax and capital gains tax entirely. For UK taxpayers, it is clean, simple, and genuinely valuable. But the moment you become a US tax resident, the picture changes completely. The IRS does not recognize the ISA wrapper. It sees straight through it to the investments inside, and it taxes everything.

This guide covers what happens to your ISA when you move to the United States, how the IRS treats it, what PFIC rules mean for your holdings, what you need to report and when, and how to think about your options going forward. It is not a guide for doing this yourself. Cross-border tax situations involving foreign investment accounts are exactly the kind of situation where professional advice is not just helpful. It is essential.

What Is a UK ISA and Why Does It Complicate Things in the US?

In the UK, an ISA is a tax-advantaged wrapper that sits around your savings or investments (as per the UK Government: Individual Savings Accounts (ISA) Official Guidance). You contribute up to an annual allowance, and everything inside grows free of UK income tax and capital gains tax. For the 2025 to 2026 UK tax year, the annual ISA allowance is £20,000. There are four main types: Cash ISAs, Stocks and Shares ISAs, Lifetime ISAs, and Innovative Finance ISAs.

The problem is that this tax treatment is a creation of UK law. HMRC says the account is tax-free. The IRS was not involved in that conversation and does not consider itself bound by it. Under US tax rules, American citizens, green card holders, and anyone considered a US tax resident must report and pay tax on worldwide income, regardless of where it is earned or held. That includes every dollar of interest, dividends, and capital gains your ISA produces each year.

Important: The US-UK tax treaty does not exempt ISAs from US taxation. It prevents double taxation on income that both countries would otherwise tax, but since the UK exempts ISA income from UK tax, only the US ends up taxing it. That means there is no foreign tax credit available to offset your US tax bill on ISA gains.

How Different Types of ISAs Are Affected

Cash ISAs

A Cash ISA functions like a savings account. The interest it earns is free of UK tax. For a US resident, that same interest must be reported on your Form 1040 and is taxed at ordinary income rates. The tax shelter disappears entirely.

Stocks and Shares ISAs

This is where things become significantly more complex. Most Stocks and Shares ISAs hold UK or European mutual funds and ETFs. A large proportion of these qualify as Passive Foreign Investment Companies under IRS rules. PFIC classification triggers one of the most punitive tax regimes in the US tax code, and it affects a great many expats who were never warned about it when they made the move.

Lifetime ISAs

The Lifetime ISA was designed for first-time home buyers or retirement savers in the UK. It carries a government bonus of up to £1,000 per year. For US residents, the same rules apply: all income and gains are fully taxable in the US, and the investments held inside may trigger PFIC reporting requirements.

The PFIC Problem: Why This Is Bigger Than Most People Expect

PFIC stands for Passive Foreign Investment Company. The IRS uses this classification to capture foreign investment funds, including most UK unit trusts, OEICs, ETFs, and mutual funds, that are not structured as US-registered securities.

If your Stocks and Shares ISA holds any of these, you may be looking at:

• Punitive tax rates on gains and excess distributions from the fund
• Interest charges applied retrospectively on deferred gains going back to when the investment was made
• Complex annual reporting on IRS Form 8621, with one form required per PFIC fund held
• Potential tax liability even in years when you sell nothing and receive no distributions

The PFIC rules catch returning Americans and British expats alike by surprise. The account appeared tax-free, no one flagged the US reporting obligations, and now years of unfiled forms have accumulated. The situation is almost always fixable, but it requires working with an adviser and a tax professional who understands both systems. The sooner you address it, the more straightforward the resolution.

US Reporting Requirements for ISA Holders

Beyond the income tax itself, holding a UK ISA as a US resident triggers several reporting obligations. Failing to file can result in significant penalties, and the IRS has been increasingly focused on foreign account compliance in recent years.

Depending on the value and structure of your account, you may need to file:

• FinCEN Form 114 (FBAR): required if your foreign financial accounts exceed $10,000 in aggregate value at any point during the calendar year
• IRS Form 8938: required for higher-value foreign financial assets under the Foreign Account Tax Compliance Act (FATCA), with thresholds that vary by filing status and residency
• IRS Form 8621: required for each PFIC fund held inside the ISA, even if you made no transactions during the year
• IRS Form 3520: potentially required if the ISA is treated as a foreign grantor trust, a classification that applies to some ISA structures under US rules

Each of these has its own filing deadlines, thresholds, and penalties for non-compliance. This is not paperwork you want to work through for the first time without expert guidance.

Can You Keep Your ISA After Moving to the United States?

Yes. Moving to the US does not force you to close your ISA. HMRC does not require closure, and your account will remain open with your UK provider. However, two things change immediately:

• You cannot make any new contributions. Only UK residents can pay into an ISA. The moment you become a non-resident, contributions stop entirely.
• The IRS begins taxing all income and gains from the account as if the ISA wrapper does not exist. Every pound of interest, dividends, and capital growth is subject to US tax.

Some providers will also restrict your investment options once they know you are based in the US. Others may refuse to hold certain funds on behalf of US persons due to regulatory restrictions. Keeping an ISA open while living in the US is legally permissible, but it comes with administrative complexity and a tax burden that many holders did not anticipate.

Whether it makes sense to keep the account, restructure it, or close it depends on what is inside, how long you plan to stay in the US, and what alternatives are available to you. That is an assessment that really needs to be done with someone who knows both systems well.

The Roth IRA: The Closest US Equivalent

The US does not have a direct equivalent of the ISA, but the Roth IRA comes closest. Contributions to a Roth IRA are made with after-tax dollars, and qualified withdrawals in retirement are entirely free of US federal income tax. Growth and income inside the account are not taxed on an annual basis.

There are meaningful differences. Roth IRA contributions are capped at $7,000 per year for most people under age 50 in 2025, and eligibility phases out at higher income levels. The account is specifically designed for retirement, and early withdrawals can trigger taxes and penalties. But for cross-border families thinking about long-term, tax-efficient savings in the US, a Roth IRA is often the starting point of the conversation.

Whether a Roth IRA, a traditional IRA, a 401(k), or another structure is right for your situation depends on your income, tax position, and whether you might eventually return to the UK (learn more about the Individual Retirement Account (IRA) for Expats). These are not decisions to make based on general information alone.

Should You Close, Keep, or Restructure Your ISA?

There is no universal answer, but here is how advisers with cross-border expertise typically think through it.

If your ISA holds cash only, the complexity is much lower. Interest is taxable in the US, but you avoid PFIC issues entirely. Some expats choose to hold a Cash ISA and simply report the income each year while keeping the account open.

If your ISA holds funds that are likely to be classified as PFICs, the annual tax and reporting burden can be significant. In many cases, moving out of those funds and into US-compliant investments, either within a restructured account or through a separate US account, is more efficient over the long term.

If you plan to return to the UK in the near future, it may make sense to hold the account and manage the US tax liability in the interim, particularly if the ISA carries a large unrealized gain you would rather not crystallize at this point.

All of these scenarios have different tax implications. A financial adviser with genuine cross-border expertise can model the outcomes specific to your situation (see our British Expats in the USA: Financial Planning Overview) and help you choose the right path, including coordinating with your tax professional on the compliance side.

FAQs – UK ISA as a US Resident

Is a UK ISA taxable in the United States?

Yes. The IRS does not recognize the UK ISA as a tax-advantaged account. All income and gains generated inside the ISA are subject to US income tax and must be reported on your annual tax return. The tax-free status granted by HMRC has no effect on your US obligations.

Do I have to report my ISA to the IRS?

Yes. Depending on the value of the account and the investments held, you may need to file an FBAR, Form 8938, and potentially Form 8621 for each PFIC fund. Non-compliance can result in significant penalties, so getting the reporting right from the start is important.

Can I still contribute to my ISA from the United States?

No. Only UK residents can make new contributions to an ISA. Once you become a US resident, your account remains open but you cannot add to it. The existing balance continues to be invested, but it will not benefit from new contributions or the annual allowance.

What if I was not aware of the PFIC rules and did not file?

This is far more common than most people realize. There are IRS procedures for catching up on unfiled PFIC forms and coming into compliance, but the process is complex and the right approach depends on your specific circumstances. You will need to work with a qualified tax adviser who handles international tax matters regularly.

Does the US-UK tax treaty protect my ISA?

No. The US-UK tax treaty does not exempt ISAs from US taxation. The treaty is designed to prevent double taxation, but since the UK does not tax ISA income, only the US taxes it. There is no foreign tax credit available to offset your US liability on ISA gains.

What is the closest US equivalent to an ISA?

The Roth IRA is most commonly cited as the closest comparison. Contributions are made with after-tax dollars and qualified withdrawals in retirement are free of US federal income tax. The contribution limits, withdrawal rules, and eligibility requirements are quite different from the ISA, however, and whether a Roth IRA fits your situation depends on factors that are worth reviewing with a qualified adviser.

Should I close my ISA when I move to the United States?

Not necessarily, and certainly not without taking advice first. The right decision depends on what you hold inside the account, your timeline for living in the US, and your long-term plans. Closing the ISA may crystallize gains. Keeping it creates US tax and reporting obligations. Neither path is obviously correct without knowing the full picture, which is exactly why speaking to a cross-border adviser before making any decisions is so important.

Your ISA and the US Tax System: Get the Right Advice. At Harrison Brook USA, we work with British expats and returning Americans every day.We help you understand what you hold, what it means under US tax law, and how to structure things correctly going forward. No jargon. No pressure. Just clear, qualified cross-border advice. Talk to one of our advisers today.

Disclaimer: This article is for informational purposes only and does not constitute legal, tax, or financial advice. Tax laws affecting cross-border situations change frequently and individual circumstances vary significantly. Please consult a qualified cross-border financial adviser and tax professional before making any decisions based on this content.