Tax Services US/UK for High Net Worth Families: What Changes at Scale

Tax services US/UK for high net worth families cover the same two annual returns everyone files, plus the information returns, payment planning, estate planning and adviser coordination that significant wealth brings. What changes at scale is the number of thresholds crossed in both countries and the cost of a decision that suits one system but not the other. This guide sets out what the work includes, where it grows and how to judge whether an adviser is set up for it.

It is written for families with at least one US citizen or green card holder and significant assets in the UK, the US or both: investment portfolios, several properties, a private company, trusts or expected inheritances. For the technical planning risks themselves, read our companion piece on where the risk sits in high net worth US/UK tax planning. This article covers the service: what you should expect a firm to do, in what order, and why.

What do tax services US/UK for high net worth families include?

Tax services US/UK for high net worth families include four layers of work: annual returns in both countries, the information returns that come with large or complex assets, tax payment and cash-flow planning, and long-range planning for gifts, trusts and estates. A family with modest savings needs mainly the first layer. A wealthy family needs all four every year.

Layer 1: annual returns

Each American family member files a US Form 1040 reporting worldwide income. Each UK-resident member with income not fully taxed at source files a UK Self Assessment return. At scale these returns carry many more schedules: dividends and interest from several custodians, capital gains from active portfolios, rental income from more than one property and income from partnerships or companies.

Layer 2: information returns

Information returns are forms that report assets or transactions rather than calculate tax. For a high net worth family they often outnumber the tax returns: the FBAR (FinCEN Form 114) for foreign accounts, Form 8938 for specified foreign financial assets, Form 8621 for each PFIC holding, Form 3520 for large foreign gifts and foreign trusts, and forms for interests in foreign companies or partnerships. Penalties for missing them can apply even when no tax is due.

Layer 3: payments and cash flow

Large tax bills fall due on different calendars. UK Self Assessment uses payments on account, and the US expects tax to be paid through the year. Planning when each payment falls, and in which currency, is part of the service.

Layer 4: planning

Planning covers gifts to children and spouses, trusts, the sale of a business or property, a move between the two countries and the estate plan. Each of these has to be checked against both tax codes and against the US-UK income tax treaty and the separate US-UK estate and gift tax treaty. Our tax services for high net worth US/UK families are built around that rule: no transaction goes ahead until both sides have been modelled.

Which thresholds change the work at scale?

The work grows because wealth crosses thresholds in both systems that ordinary filers never reach. The table below lists the main ones, each with the figure for the year stated and a link to the official source.

Threshold	Figure	What it triggers
FBAR	Foreign accounts above $10,000 in aggregate at any time in the calendar year	FinCEN Form 114, due 15 April with an automatic extension to 15 October (IRS)
Form 8938, living abroad	Single filer: more than $200,000 at year end or $300,000 at any time; joint filers: $400,000 or $600,000	Statement of specified foreign financial assets with the Form 1040 (IRS)
Net Investment Income Tax	Modified adjusted gross income above $200,000 (single) or $250,000 (married filing jointly); not indexed for inflation	An extra 3.8% US tax on investment income (IRS)
Foreign gifts	More than $100,000 in a tax year from a nonresident alien individual or foreign estate	Form 3520; late reporting can cost 5% of the gift per month, up to 25% (IRS)
US gift tax annual exclusion, 2026	$19,000 per recipient; $194,000 for gifts to a spouse who is not a US citizen	Form 709 for gifts above these amounts (Rev. Proc. 2025-32)
UK additional rate, 2026/27	Income above £125,140 taxed at 45%; the Personal Allowance is reduced once income passes £100,000	Higher marginal rates and a lost allowance (GOV.UK)
UK Inheritance Tax	40% above the £325,000 threshold	Estate planning in the UK as well as the US (GOV.UK)

Two further UK changes matter most to investment-heavy families. From 6 April 2026 the UK dividend ordinary rate rose to 10.75% and the upper rate to 35.75%, with the additional rate staying at 39.35% (GOV.UK). For 2026/27, UK Capital Gains Tax is charged at 18% and 24% for individuals, with an annual exempt amount of £3,000 (GOV.UK). Because US rates and UK rates on the same dividend or gain differ, the foreign tax credit calculation on the US return becomes one of the most valuable parts of the work.

How the estate picture changes for high net worth families

The US and UK estate systems reach very different estates. For calendar year 2026 the US estate and gift tax basic exclusion amount is $15,000,000 per person (IRS). UK Inheritance Tax, by contrast, is charged at 40% above a £325,000 threshold. A family can therefore be well inside the US exclusion and still have a large UK Inheritance Tax exposure.

Since 6 April 2025, UK Inheritance Tax on assets outside the UK depends on long-term UK residence rather than domicile. HMRC's manual explains that a person is a long-term UK resident when they have been UK resident for at least 10 of the last 20 tax years, and that the status continues for a period after they leave (IHTM47020). An American who has lived in London for a decade is likely to be within UK Inheritance Tax on their US brokerage account, US property and US retirement accounts.

The US-UK estate and gift tax treaty then decides which country has the first right to tax each asset and how credits work, as explained in our guide to the US-UK estate tax treaty. Wills, trusts and lifetime gifts must be written with both systems in mind; our trusts and estates service works with the family's lawyers in each country to do that.

Is the FIG regime useful for a wealthy American moving to the UK?

The 4-year foreign income and gains (FIG) regime is useful on the UK side only. It lets a qualifying new UK resident claim relief from UK tax on foreign income and gains for up to four tax years, provided they were not UK resident for at least ten consecutive years before arriving (GOV.UK). It replaced the remittance basis for new arrivals from 6 April 2025.

For a US citizen the regime does nothing to US tax, which continues to apply to worldwide income every year. That creates a planning point many people miss: during the FIG years there may be little or no UK tax on foreign income, so there is little UK tax to credit against US tax on that income. Timing gains, dividends and pension withdrawals across the four years and the years after needs both returns modelled together. The relief is not automatic: it has to be claimed on the UK return. Our article on the non-dom changes for Americans in the UK covers the rules in detail.

What do people get wrong when buying high net worth tax services?

The most common mistake is buying two separate services and assuming they will join up. A US preparer and a UK accountant who never speak can each file a correct return while the family overpays, misses relief or creates a problem in the other country. These are the patterns we see most often:

• Investment managers choosing funds without the US position. UK-domiciled funds and investment trusts are generally passive foreign investment companies (PFICs) for US tax, reported on Form 8621. Our worked example of the PFIC excess distribution calculation shows how quickly the charge grows.
• Gifts made before the tax check. A transfer to a non-US-citizen spouse above the $194,000 annual limit for 2026, or to a child, can need a US gift tax return, and a gift to a child may also start the UK seven-year clock for Inheritance Tax.
• Trusts drafted for one country only. A UK trust with US beneficiaries brings US foreign trust reporting, and a trust drafted only under US conventions can create UK Inheritance Tax consequences nobody intended.
• No cash plan for tax bills. UK payments on account are each normally half of the previous year's bill, due on 31 January and 31 July (GOV.UK), while US tax is due through the year. A large sale in one year can create payments in both countries in the next.
• Keeping exit options open by accident. Renouncing US citizenship with a net worth of $2 million or more on the expatriation date makes a person a covered expatriate under the exit tax rules (IRS Form 8854 instructions). Families who may consider it one day benefit from knowing this when they plan gifts and trusts.

How to choose tax services US/UK for high net worth clients

Choose a firm that can show it will own both sides of the family's position, not just prepare forms. Use these steps to compare advisers:

1. Ask who is answerable for both countries. One lead adviser, or one team covering both countries, should sign off every recommendation. "We will liaise with your other accountant" is a weaker answer.
2. Ask for a written scope that lists every filing. It should name each person, each return, each information return and each due date for the year, in both countries.
3. Test their knowledge of the specific assets. Ask how they would report your UK funds, your pensions, your trust and any private company. Specific answers show experience; general reassurance does not.
4. Ask how they coordinate other advisers. Lawyers, private bankers and investment managers in both countries should know who to call before a transaction.
5. Ask how fees are set. A fixed annual fee for the compliance layer, with planning projects priced separately, makes costs predictable. Hourly billing can suit one-off advice.
6. Ask what happens before a big decision. The answer should be: both returns are modelled first, and the decision is written up with the treaty articles and rules it relies on.

US/UK Cross Border Tax works this way: US CPAs and UK tax advisers working as one team, with offices in London, Manchester, New York and San Francisco. Our private client service covers the compliance and planning layers together, and our broader guide to tax services US/UK maps the full service list.

A year of high net worth US/UK tax services: illustrative example

Illustrative example: a married couple live in London. One spouse is a US citizen who has been UK resident for twelve years; the other is British. They hold a US brokerage account, a portfolio of UK funds, two UK rental flats and a family trust set up by a British grandparent. Over one year, their tax services would typically include: two UK Self Assessment returns with the property and foreign income pages; a US Form 1040 for the American spouse, filed married filing separately unless a joint election is better; an FBAR and Form 8938; a Form 8621 for each UK fund; foreign trust reporting if the American spouse is a beneficiary who receives a distribution; a review of the American spouse's estate, which is likely to be within UK Inheritance Tax on worldwide assets as a long-term UK resident; and a check before any gift between the spouses. This is an illustration of scope, not a description of any real client.

The example shows why the work is a single plan rather than a stack of forms. The choice of filing status, the treatment of the funds and the trust, and the estate plan all affect one another, and each should be decided once, with both systems in view.

The bottom line

Tax services US/UK for high net worth families are judged less by any single return than by whether the whole position holds together: every filing made, every threshold tracked, and every major decision tested in both countries before it happens. If your family's wealth now spans both countries and you are not sure your current advisers are coordinating, contact our team for a review of your scope and calendar.