UK Self Assessment Registration for Americans

Most Americans who move to the UK need to register for Self Assessment, even on a salary taxed through PAYE, because US bank interest, dividends and capital gains are foreign income that PAYE never touches. HMRC's rule is to register by 5 October after the end of the tax year in which that income arose.

The surprise for newly arrived Americans is that the UK system is built the opposite way round from the US one. In the United States everyone files. In the UK most employees never file at all, because PAYE settles their tax at source. HMRC only expects a return when something falls outside PAYE, and for an American with even a modest US brokerage or savings account, something almost always does. This article covers when you have to register, how to do it, and the US-specific decisions that start with that first return.

Key takeaways

• PAYE does not cover your US income. Interest from a US checking or savings account, US dividends and gains on US investments are foreign income, and reporting them usually means a Self Assessment return.
• The registration deadline is 5 October following the end of the UK tax year (6 April to 5 April) in which you first need to file, according to HMRC's own guidance on GOV.UK.
• New arrivals may be able to claim the 4-year foreign income and gains (FIG) regime, but only through a Self Assessment return, and claiming it costs you the UK personal allowance for that year.
• Your first return is where split-year treatment is claimed, so the arrival year is often the year registration matters most.
• Your US return does not stop. The UK return and the US return are two separate obligations covering different tax years, and the order you prepare them in affects your foreign tax credits.

Do you need to register for Self Assessment if you are paid through PAYE?

Not always, but usually. GOV.UK's guidance on tax on foreign income says you usually need to fill in a Self Assessment return if you are a UK resident with foreign income or capital gains. It sets out a narrow exception: you do not need a return if your only foreign income is dividends, your total dividends including UK ones are below the £500 dividend allowance (2026-27), and you have nothing else to report.

That exception rarely fits an American. The common triggers we see in a first UK year are:

| Trigger | Why it usually needs a return |

|---|---|

| Interest on a US bank or high-yield savings account | Foreign interest, not taxed through PAYE |

| Dividends from US shares or US mutual funds | Foreign dividends; the exception above only covers small, dividend-only cases |

| Selling US shares, funds or a US home | Foreign capital gains |

| Rent from a US property you kept | Foreign property income |

| Self-employment or freelance work | Outside PAYE whatever its source |

| Arrival part-way through the tax year | Split-year treatment is claimed on the return |

| Wanting the FIG regime | The claim can only be made on a return |

If none of those applies and your only income is a UK salary, you may genuinely have nothing to file. GOV.UK has a check if you need to send a tax return tool, and it is worth running once your first tax year ends.

When is the deadline, and which tax year does it refer to?

The UK tax year runs from 6 April to 5 April, not January to December. HMRC's register for Self Assessment page states that you must tell HMRC by 5 October following the tax year you need to file for, if you have not sent a return before. For the 2025-26 tax year (6 April 2025 to 5 April 2026), that date was 5 October 2026. HMRC warns that telling it later can lead to a penalty.

Registration is only the first step. The return itself is due online by 31 January after the end of the tax year, which is also when any tax owed is payable, per GOV.UK's Self Assessment deadlines page.

| Step | Date for income in 2026-27 (6 Apr 2026 – 5 Apr 2027) | Source |

|---|---|---|

| Register for Self Assessment | 5 October 2027 | GOV.UK, register for Self Assessment |

| File the online return | 31 January 2028 | GOV.UK, Self Assessment deadlines |

| Pay the balance owed | 31 January 2028 | GOV.UK, Self Assessment deadlines |

The mismatch with the US calendar year is the part that trips people up. A single UK tax year straddles two US tax years, so the same dividend can sit on your 2026 US return and your 2026-27 UK return at the same time.

How do you actually register as a US citizen?

Registration is done on GOV.UK. In practice you will need:

• A UK National Insurance number. HMRC identifies you by this. Your US Social Security number plays no part in the UK system.
• A Government Gateway account, created during the online process.
• Your UK address and contact details, and the date your UK income or residence began.

Once registered, HMRC issues a Unique Taxpayer Reference (UTR), a ten-digit number, by post. Your UTR is what you, your adviser and HMRC use for every return from then on. If you register before your UTR arrives and the deadline is close, record the date you registered; HMRC's guidance explains how to check when to expect a reply.

If you arrived without a National Insurance number, apply for one first, because registration is far simpler with it. Keep evidence of when you started the process in case the timing is ever questioned.

Should a newly arrived American claim the 4-year FIG regime?

Since 6 April 2025, the remittance basis has been replaced by the 4-year foreign income and gains regime. HMRC's guidance on checking whether you can claim the 4-year FIG regime says it is available if you are UK resident under the statutory residence test and within your first four years of UK residence after at least ten consecutive years of non-UK residence. Most Americans arriving for the first time meet that description.

The regime is claimed on your Self Assessment return, so it is a reason to register, not a reason to skip it. HMRC lists the cost: claiming means losing the Income Tax personal allowance (£12,570 for 2026-27) and the Capital Gains Tax annual exempt amount for that year. Foreign employment earnings are outside the regime altogether.

For a US citizen, the decision is less obvious than it is for other new arrivals, because the United States taxes the same income regardless:

• If you claim FIG, the UK does not tax your eligible US interest, dividends and gains. The US still does, and with no UK tax paid on that income there is no UK tax to credit against it on Form 1116. You have also given up your personal allowance on your UK salary.
• If you do not claim, the UK taxes the US income, and that UK tax can often be credited on your US return, subject to the treaty's re-sourcing rules and the Form 1116 limitation.

Which leaves you better off depends on the size of your US investment income against your UK salary, and it has to be modelled across both returns. It is exactly the kind of interaction we cover on our US–UK cross-border tax specialists page.

What goes on an American's first UK return?

The main return is the SA100. For a typical American arrival, the supplementary pages that come up are:

• SA106 (Foreign) for US interest, dividends, US property income and foreign tax already paid.
• SA109 (the residence pages) to claim split-year treatment in the arrival year and, where relevant, to make the FIG claim.
• SA108 (Capital gains) if you sold US investments or property after becoming UK resident.

Split-year treatment matters in the arrival year. Without it, a UK resident is taxed for the whole tax year; with it, the year is divided so that the part before you arrived is treated as overseas. Our article on the moving-year tax return between the US and the UK explains how split-year treatment and the US side interact in that first year.

What about your US return?

Registering in the UK does not change your US position. As a US citizen or green card holder you still file Form 1040 every year, report your UK salary, and claim either the foreign earned income exclusion (Form 2555) or foreign tax credits (Form 1116). You also file an FBAR for your UK accounts if their combined value crosses the reporting threshold.

Because the UK return covers 6 April to 5 April and the US return covers January to December, the order in which you prepare them affects how much UK tax is available to credit. Our guide on which tax return to file first, US or UK works through that sequencing.

How Next Tax Source helps new arrivals

We register you with HMRC, decide with you whether a FIG claim makes sense once both returns are modelled, prepare the SA100 and its supplementary pages, and prepare the matching US return so the two agree. Every return is reviewed by our IRS Enrolled Agent, who is also ACCA-qualified, and you approve and submit it yourself. If you arrived in the UK this year and hold anything in the US, book a consultation well before 5 October.