US Tax Help for Wealthy Britons Living in Boston Wealthy Britons who move to Boston become subject to U.S. tax on their worldwide income once they meet the substantial presence test or hold a green card. Specialist US tax help in Boston matters because Massachusetts levies up to 9% at the state level, and everyday […]
Wealthy Britons who move to Boston become subject to U.S. tax on their worldwide income once they meet the substantial presence test or hold a green card. Specialist US tax help in Boston matters because Massachusetts levies up to 9% at the state level, and everyday UK assets like ISAs turn into punitive US tax problems overnight.
By the Jungle Tax Cross-Border Tax Team — reviewed by a US-UK dual-qualified adviser (CPA / Enrolled Agent).
You become a US tax resident the moment you either receive a green card or meet the IRS substantial presence test. From that point, the United States taxes your entire worldwide income, not merely what you earn inside America. This is the single fact that catches most affluent arrivals off guard, and it is the reason so many search for reliable US tax help in Boston within weeks of landing.
The substantial presence test counts all your days in the US this year, one-third of your days last year, and one-sixth of your days the year before. If the weighted total reaches 183 days and you have spent at least 31 days here this year, you are a resident for tax purposes. Many people cross that line without noticing, especially if they visited on business before relocating.
The green card route is even simpler to trip over. Lawful permanent residents are US tax residents from the day their status is granted, regardless of how many days they actually spend in the country. A wealthy Briton who obtains a green card to work in Boston is immediately within the US net, with no day-counting relief available.
UK rental income, UK dividends, interest on your building society account, capital gains on your London flat, and distributions from your investment portfolio all become reportable on a US federal return. The US-UK double tax treaty and the foreign tax credit prevent most double taxation, but they do not remove the reporting obligation. Getting the first filing correct is where good US tax help in Boston earns its fee.
Currency movement adds a hidden trap. The IRS assesses gains in US dollars, so a mortgage repayment or a fund sale can generate a taxable foreign-exchange gain even when nothing has changed in sterling terms. A weakening pound during your holding period can quietly create a US liability that never appears on your UK return, which is another reason coordinated support looks at the dollar figures, not just the sterling ones.
Massachusetts applies a flat 5% income tax to residents, then adds a 4% surtax on taxable income above an inflation-indexed threshold of $1,107,750 for tax year 2026. For a wealthy Briton, that combined 9% top rate sits entirely outside the US-UK treaty, because tax treaties bind the federal government, not individual states. Massachusetts does not have to honor treaty positions, foreign tax credits, or federal exclusions.
This state-level gap is why generic advice fails in Boston. A treaty election that shields income from federal tax can still leave that same income fully exposed to Massachusetts. Coordinated US tax help Boston looks at federal and state consequences together, rather than solving one and creating a problem in the other.
|
Income level (2026) |
Massachusetts rate |
Notes
|
|---|---|---|
|
Up to $1,107,750 |
5% flat |
Applies to most residents’ income |
|
Above $1,107,750 |
9% (5% + 4% surtax) |
Surtax hits only the portion over the threshold |
The surtax threshold is indexed each year. It rose from $1,083,150 in 2025 to $1,107,750 in 2026, so anyone with a large one-off event, such as selling a business or exercising options, should model the timing carefully.
This is the most expensive surprise for wealthy Britons, and it is where dedicated cross-border advice pays for itself many times over. ISAs receive no special treatment from the IRS. The tax-free wrapper you enjoy in Britain simply does not exist in the US, so the underlying income and gains are fully taxable there.
Worse, most UK funds, unit trusts, OEICs and investment trusts are treated as Passive Foreign Investment Companies, or PFICs. The PFIC regime under section 1291 is deliberately punitive: it can tax gains at the highest marginal rate, apply an interest charge for every year you held the fund, and demand complex annual reporting on Form 8621 for each fund you own.
Pre-immigration planning is the difference between a clean start and a costly clean-up. Before your US residency clock starts, there is often a window to sell PFIC holdings, crystallize gains at UK rates, and restructure into US-compliant investments. Once you are a US resident, those same moves trigger American tax. This is precisely why we urge clients to seek this help before they board the plane, not after.
Two federal reporting regimes catch nearly every wealthy Briton. The first is the FBAR, which is filed when your foreign financial accounts exceed $10,000 in aggregate at any point during the year. The second is Form 8938 under FATCA, which, for a married couple living abroad, kicks in at $400,000 on the last day of the year, though the thresholds fall sharply once you are physically present in the US.
These are information returns, not tax bills, but the penalties for missing them are severe. Willful FBAR failures can attract penalties measured as a percentage of the account balance. UK rental income sits on Schedule E, and your UK pension needs careful treaty analysis rather than a guess.
|
Form |
Triggered by |
Filed with
|
|---|---|---|
|
FinCEN 114 (FBAR) |
Foreign accounts over $10,000 aggregate |
FinCEN, separate from tax return |
|
Form 8938 |
Specified foreign assets over the threshold |
Attached to Form 1040 |
|
Form 8621 |
Each PFIC held (UK funds, OEICs, ISAs) |
Attached to Form 1040 |
UK pensions, including a SIPP, usually enjoy protection under the US-UK treaty, but the treatment is not automatic. Growth within the pension, the tax-free lump sum, and drawdown timing all require a treaty position to be taken on the return. Getting this wrong can convert a protected pension into a currently taxable one.
The 25% tax-free lump sum deserves particular caution. It is genuinely tax-free in Britain, yet the US may treat it as ordinary income unless the treaty position is correctly and consistently claimed. Drawing that lump sum in a year when you are already a US resident, rather than before you arrive, can turn a tax-free benefit into a taxable one worth tens of thousands. Employer and workplace pensions raise similar questions, and each scheme needs to be assessed on its own terms rather than lumped together.
When the same income is taxed in both countries, the foreign tax credit lets you offset UK tax paid against your US liability. Because UK income tax rates often exceed US federal rates, many clients carry forward excess credits. HMRC’s own guidance on tax on foreign income mirrors this from the British side.
The credit is powerful but imperfect. It does not apply cleanly at the Massachusetts state level; it does not rescue PFIC income taxed at penalty rates, and it requires careful sourcing of each income type. Good planning sequences income and credits so nothing is wasted.
Domicile, not residency, drives US estate and gift tax, and a wealthy Briton who intends to remain in Boston can acquire US domicile without realizing it. Once US-domiciled, your worldwide estate falls under the federal system, which currently offers a $15,000,000 exemption per person for 2026, following the One Big Beautiful Bill Act.
Massachusetts adds its own layer. The state imposes an estate tax above $2,000,000, with graduated rates ranging from 7.2% to 16%, and it does not track the generous federal figure. A Boston estate can therefore owe Massachusetts tax while owing nothing federally. Lifetime gifting, trust structuring, and domicile planning all deserve early attention.
A British technology founder, whom we will call James, accepted a role in Boston and planned to sell a stake in his UK company soon after arriving. He held a stocks-and-shares ISA worth around £320,000, two UK index funds, and a SIPP.
Because he engaged us three months before his move, we crystallized his ISA and fund gains at UK rates while he was still solely UK-resident, avoiding the PFIC section 1291 charge entirely. We timed his share sale to fall in a UK-only tax year, sidestepping both the US federal charge and the Massachusetts 4% surtax. We then filed a protective treaty position on his SIPP. The pre-immigration work saved a projected six-figure sum against the outcome had he simply arrived and filed later.
If you are a wealthy Briton relocating to Boston, the time to plan is before your US residency begins. Jungle Tax specializes in US-UK cross-border tax and works with founders, executives, and creative professionals on exactly these questions
.
Email hello@jungletax.co.uk, call 0333 880 7974, or visit jungletax.co.uk to arrange a confidential pre-immigration review. You can also read our related guides on US-UK cross-border tax, PFICs and UK funds, American expat tax, UK pensions under the US treaty, and pre-immigration tax planning.
In practice, US tax help in Boston is the exact scenario our cross-border specialists resolve every week.
Do I have to pay US tax on my UK income if I live in Boston?
Yes. Once you are a US tax resident, the United States taxes your worldwide income, including UK rent, dividends, and gains. The foreign tax credit usually prevents double taxation, but you must still report everything.
Are my ISAs really taxable in the United States?
Yes. The IRS does not recognize the ISA wrapper, so income and gains held in an ISA are taxable in the US. Many ISA holdings are also PFICs, which are subject to punitive treatment and additional reporting on Form 8621.
What is the substantial presence test?
The IRS day-counting rule determines US tax residency. It weighs your US days across the current year and the two prior years, and you become a resident if the weighted total reaches 183 days.
How much is Massachusetts income tax for high earners?
Massachusetts charges a flat 5% tax, plus a 4% surtax on taxable income above $1,107,750 for 2026, resulting in a 9% top rate. This state tax sits outside the US-UK treaty.
Will I owe US estate tax on my UK assets?
If you become US-domiciled, your worldwide estate falls within the federal system, which has a $15,000,000 exemption for 2026. Massachusetts also taxes estates exceeding $2,000,000, so state exposure can arise even without federal liability.
Do I need to file an FBAR for my UK bank accounts?
Yes, if your foreign accounts together exceed $10,000 at any point in the year. The FBAR is an information return filed with FinCEN, and penalties for failing to file it can be severe.
