UK Tax Return for Expats: Self-Assessment Guide 2026

For many British expats, the UK self-assessment tax return remains an annual obligation long after they have left the country. Whether you are a non-resident landlord, receive UK pension income, hold UK investments, or left mid-year and triggered split-year treatment, HMRC's self-assessment system still applies to you. This guide explains who must file, what to declare, how to meet the deadlines from abroad, and the mistakes that cost expats thousands of pounds each year.

Who Must File a UK Self-Assessment Return as an Expat?

Not every expat has a UK tax return obligation, but the circumstances that create one are surprisingly common:

Non-resident landlords. If you own UK property and receive rental income, you are almost certainly required to file a self-assessment return, even if you have registered under the Non-Resident Landlord (NRL) scheme and have tax deducted at source by your letting agent. The NRL scheme only covers withholding — it does not replace the return.

UK-source investment income. Dividends from UK companies, interest from UK bank accounts, and income from UK trusts or settlements may create a filing obligation. The thresholds are low: if your untaxed income exceeds £1,000, you will generally need to file.

UK pension income. State pension, occupational pension, and annuity income paid to non-residents is taxable at source for most recipients, but self-assessment may still be required to claim treaty relief, ensure the correct rate has been applied, or declare other income.

Capital gains on UK assets. From April 2015 (residential property) and April 2019 (all UK land), non-residents became liable to UK Capital Gains Tax (CGT) on disposals of UK real estate. Such gains must be reported within 60 days via the UK Property Reporting Service, but a self-assessment return is also typically required. Gains on UK shares are generally outside the scope for non-residents, though there are exceptions.

Split-year treatment. In the year you leave or arrive in the UK, split-year treatment divides your tax year into a UK-resident part and a non-resident part. A return is mandatory in split years to calculate your liability correctly.

High-income taxpayers with certain deductions. If you are UK-resident for part of the year and have complex affairs — multiple income sources, pension annual allowance issues, or Gift Aid to claim — a return will be required.

If you are uncertain whether you need to file, the safest course is to register for self-assessment and file a return. HMRC's records may already show UK income that they expect you to declare.

Key Deadlines for UK Self-Assessment

The UK tax year runs from 6 April to 5 April. Deadlines are fixed regardless of where in the world you live:

• 31 October (following the end of the tax year): paper return deadline
• 31 January (following the end of the tax year): online return deadline and payment of any tax due
• 31 July: second payment on account (for those who make payments on account)

For example, the return for the tax year 6 April 2025 to 5 April 2026 must be submitted online by 31 January 2027, with any outstanding tax paid by the same date.

There is no extension for non-residents. The 31 January deadline applies universally, whether you live in Dubai or Sydney. A common mistake is assuming that being abroad grants additional time — it does not. If you are late, automatic penalties begin immediately.

Registering for Self-Assessment

If you have not previously filed a UK return, you must register with HMRC before you can submit one. Registration should be completed by 5 October following the end of the relevant tax year. For most expats, this means registering by 5 October 2026 for the 2025–26 tax year.

To register:

1. Go to HMRC's website and use the SA1 form (or register online via Government Gateway).
2. Provide your National Insurance number, UK address history, and reason for registering.
3. HMRC will issue a Unique Taxpayer Reference (UTR) — this can take several weeks, so do not leave registration late.

If you have previously filed a return but stopped (for example, when you left the UK), you may need to re-register. HMRC sometimes de-registers individuals who have not filed for several years.

What to Declare on a UK Return as a Non-Resident

The scope of your return depends on your residency status and tax treaty position.

Non-residents are taxable on UK-source income only. Unlike UK residents who are taxed on worldwide income, non-residents pay UK tax only on income arising in the UK. This typically includes:

• Rental income from UK property
• Dividends from UK companies (subject to treaty rates)
• Interest from UK bank and savings accounts
• UK employment income for work performed in the UK
• Pension income from UK schemes
• Income from UK estates in administration

Foreign income is generally not reportable. A non-resident does not declare foreign employment income, foreign dividends, or foreign rental income on a UK return. (Note that the remittance basis and the non-domicile regime were abolished from 6 April 2025 and replaced by a four-year Foreign Income and Gains regime for new arrivers to the UK — so the old "non-dom" framing no longer applies to current years.)

The return includes supplementary pages for different income types. Non-residents typically complete the SA109 (Residence, remittance basis, etc.) in addition to the main SA100 form.

The SA109: The Non-Resident's Key Supplementary Page

The SA109 is where non-residents declare their residence status and claim treaty relief. This page cannot be filed through HMRC's free online service — it requires third-party software or a paper return. Many expats are caught out by this limitation and inadvertently file an incomplete return.

Key sections of SA109 include:

• Confirmation of statutory residence test outcome
• Split-year treatment claim (if applicable)
• Claims for personal allowances under a tax treaty
• Certification of non-residence status for treaty purposes

Note on personal allowances: non-residents do not automatically receive the UK personal allowance (£12,570 as of 2026). You may claim it if you are a citizen of a country with a double-taxation agreement that provides for personal allowances, or if you are a Crown employee, EEA national, or resident of certain territories. Without it, UK-source income is taxed from the first pound.

Paying UK Tax from Abroad

Once your return is submitted, any tax due must be paid by 31 January. HMRC accepts payment by:

• Online banking (faster payment or BACS)
• International bank transfer (using HMRC's bank account details and your UTR as reference)
• Debit or corporate credit card via HMRC's website

Be aware of currency costs. If you are paying in a currency other than sterling, your bank's exchange rate and transfer fees can add meaningfully to the total. Some expats use foreign exchange services to obtain better rates when making large payments.

Payment on account applies if your self-assessment liability exceeds £1,000 and tax collected at source is less than 80% of the total. In such cases, HMRC requires advance payments — 50% on 31 January and 50% on 31 July — based on the prior year's liability. This can create a significant cash flow demand in the first year of filing.

Common Mistakes Made by Expat Filers

Assuming HMRC will not find out. HMRC receives data automatically under the Common Reporting Standard (CRS) and FATCA. Banks in over 100 countries report UK nationals' account balances and income to HMRC. Rental income is often reported by letting agents. The era of undisclosed offshore income is over.

Missing the 60-day UK property reporting deadline. Since April 2020, disposals of UK residential property by non-residents must be reported and any CGT paid within 60 days of completion. Missing this deadline triggers an automatic penalty, separate from the annual self-assessment obligations.

Overclaiming the personal allowance. Some non-residents claim the allowance without checking treaty eligibility. HMRC can challenge this and seek repayment with interest and penalties.

Filing the wrong year. The UK tax year differs from calendar years used in most other countries. An expat who left in August 2025 needs to file for the year ended 5 April 2026 (covering the split year) and for 5 April 2025 (the final full resident year, if not already filed).

Ignoring payments on account. Receiving a large demand for a past year's liability plus two payments on account simultaneously can cause severe cash flow problems. Planning ahead with a tax adviser avoids unpleasant surprises.

Using a UK Tax Adviser from Abroad

Given the complexity of non-resident UK tax, most expats benefit from professional assistance. A UK-qualified tax adviser or accountant (look for ICAEW or CIOT membership) with experience of non-resident clients will:

• Confirm whether you need to file and on which basis
• Complete SA109 correctly
• Identify treaty relief available
• Review your overall position for planning opportunities
• Represent you in any HMRC enquiry

Many reputable firms now offer fully remote services. Bear in mind that tax advice is not regulated in the same way as financial advice, so credentials and membership of a professional body matter.

Compliance as of 2026

HMRC has significantly increased its compliance activity targeting non-residents, particularly in respect of undisclosed rental income, CGT on property, and the former non-dom regime. Voluntary compliance, timely filing, and accurate disclosure remain by far the most cost-effective approach. HMRC's various disclosure facilities — including the Worldwide Disclosure Facility — exist for those with past irregularities, but penalties increase substantially if HMRC opens an enquiry before you come forward.

As always with international tax matters, rules change and individual circumstances vary enormously. This article reflects the position as of 2026 but should not be treated as personal advice. Always seek specialist guidance for your specific situation.

How Global Investments Can Help

Global Investments has worked with internationally mobile clients for over 32 years. Our team understands the intersection of UK tax obligations and global wealth management. Whether you need a referral to a specialist UK tax adviser, guidance on structuring your UK assets to minimise ongoing obligations, or help understanding how your UK affairs interact with your host-country tax position, we can help.

We work with clients across the international markets in which they invest and reside, and can co-ordinate advice across jurisdictions to ensure your overall position is managed efficiently and compliantly. Contact our team to arrange a confidential consultation.

This article is for general information only. Tax rules are complex and change frequently. Nothing here constitutes personal tax or legal advice. You should seek independent professional advice tailored to your circumstances. Investments can fall as well as rise in value.