Staying on Top of Your UK Expat Tax Paperwork

If you’ve just moved to the UK – or you’re about to – there’s probably a long list of things you’re trying to sort out. Housing, banking, healthcare…and then there’s taxes.

Getting your taxes sorted isn’t exactly exciting, but getting your head around it early saves you from annoying setbacks later.

A big part of what makes taxes such a nuisance – especially in a new country – is the paperwork. There are forms to register, deadlines to track, and documents to keep on hand. It’s all too easy to miss something or assume a form doesn’t apply to you.

But getting up to speed with the what, where, and when of expat tax paperwork means you can take care of it early and start enjoying your new life in the UK with peace of mind.

Registering to Pay UK Tax

Before you can file anything or pay tax in the UK, you need to be registered with HMRC – the official UK tax system. 

For most expats, this starts with creating an account through HMRC’s online portal. Once that’s set up, you can register for the services you need and carry out your UK tax obligations.

Common setup steps include:

• Applying for a National Insurance (NI) number: Needed if you’re working in the UK. You can see a full list of the documents needed for your registration in our free guide here. 
• Registering for Self Assessment: Required if you’re self-employed, earning foreign income, or not taxed fully through payroll. Note: You do not need to register just for foreign income if your only foreign income is dividends and they are fully covered by the £500 dividend allowance for 2025-26, and you have nothing else that would require a tax return.

Reporting What You Earn

If you’re employed in the UK, most of your tax is handled automatically through Pay As You Earn (PAYE). But if you’re self-employed or freelancing, you’ll usually need to report this yourself through Self Assessment.

Note: Even if tax is deducted from your salary through PAYE, many expats still need to register for Self Assessment to declare income that isn’t fully taxed through payroll – like earning income from abroad, renting out property, or any other untaxed income sources.

Your Self Assessment tax return is built around the SA100, which is the main form. You then add extra sections depending on how you earn your money:

• SA102 (If you’re employed – for salary, bonuses, benefits in kind, company cars, and other employment income taxed through PAYE)
• SA103 (If you’re self-employed or freelancing)
• SA105 (If you rent out property or land in the UK – including buy‑to‑let and some holiday lets)
• SA106 and SA109 (Covering foreign income and your residency status)
• SA108 (Reports asset sales and calculates Capital Gains Tax – like when you sell property other than your main home, shares, or crypto. These gains usually need to be included in your UK tax return.)

If you’re employed, your employer will also give you documents, like a:

• P60 (Your end-of-year summary)
• P45 (When you leave a job) or 
• P11D (If you receive benefits like private health insurance) 

You don’t submit these with your tax return, but you use the figures on them to fill in the employment section, and you should keep them as proof.

Note for 2026: If you’re a sole trader or landlord with a total qualifying income over £50,000, (based on your gross self-employment turnover and/or gross rental income, not your profit), you now fall under Making Tax Digital (MTD). This means you must keep digital records and send updates to HMRC every quarter using compatible software, rather than just filing once a year.

Claiming Reliefs, Refunds, and Adjustments

If you’ve paid too much tax, earned money outside the UK, or qualify for certain allowances, there are ways to sort it all out. The catch is that HMRC usually won’t flag these things for you. You need to know what applies to your situation and make the right claims yourself.

This can include:

Claiming the 4-year FIG Regime

If you’re a new UK tax resident (and haven’t lived in the UK for the last 10 years), you can claim this via Self Assessment. It allows you to bring foreign income and gains into the UK tax-free for your first four years of residence.

The claim must be made by 31 January in the second tax year after the year concerned.

For example, for the 2025-26 tax year, the deadline to claim is 31 January 2028.

Claiming Double Taxation Relief

If you’ve already paid tax on the same income in another country, you can usually claim relief under the relevant double taxation agreement. This is usually declared on your SA106 form and helps reduce your UK tax bill so you’re not paying income tax twice on the same earnings.

But keep in mind that: 

• Foreign employment income taxed overseas is normally declared on SA102 (Employment) alongside SA106
• Foreign pensions or annuities that have already been taxed abroad are generally reported on the main return SA100, with relief applied through SA106

Fixing Mistakes on a Return

You can usually amend your return online within 12 months of the filing deadline.

Applying for a Tax Refund

If you don’t file a Self Assessment tax return, you can normally claim a refund using HMRC’s online “Claim a Tax Refund” service, or by using the specific form for your situation. For example:

• R40 for tax on savings and investment income
• P85 if you’ve left the UK part-way through the tax year
• R43 if you live abroad but are due UK tax back
• R38 for other Income tax overpayments

Key UK Tax Deadlines

• The UK tax year: Runs from 6 April to 5 April each year.
• Registering for Self Assessment: Must be done by 5 October following the end of the tax year you’re reporting.
• Filing your UK tax return: Paper return must be filed by 31 October following the end of the tax year, while online returns have until 31 January following the end of the tax year to be submitted.
• Paying your Self Assessment bill: Any tax due for the year must be paid by 31 January following the end of the tax year.
• Payments on Account: If your Self Assessment tax bill is over £1,000, and less than 80% of your tax is collected at source, HMRC usually asks you to make two advance payments toward next year’s tax. The first payment is due 31 January, and the second on 31 July. Each payment is normally 50% of your previous year’s tax bill. These aren’t extra taxes – they’re advance payments toward what you’re expected to owe next year.

If You Fall Under Making Tax Digital (Starting April 2026)

If you earn over £50,000 from self-employment or rent, you’ll start the new digital system on 6 April 2026. You’ll still do a final annual declaration by 31 January, but you must now send quarterly updates by the 7th of the month (not the 5th):

• 7 August: For the quarter ending 5 July
• 7 November: For the quarter ending 5 October
• 7 February: For the quarter ending 5 January
• 7 May: For the quarter ending 5 April

Proof and Record-Keeping

HMRC has a long memory. They can ask questions about your filings years after the fact. Unfortunately, they won’t accept “I missed the email” as an excuse. You’ll need to keep a solid secure folder (digital, physical, or both) containing:

• Submission receipts: Any time you file something online, save the confirmation email or reference number. This is your proof that you actually submitted it.
• The P forms: Keep every P60 (your end-of-year summary) and P45 (what you get when you leave a job) your employer gives you.
• Bank evidence: If you’re moving money from overseas or earning income abroad, keep statements that show where the money came from, when it arrived, and how much it was.
• Tax calculations and letters: Download copies of any HMRC issues, plus any letters or messages you receive through your online account.

Future you will be very grateful you took this step!

UK Tax Support for Expats

Moving to the UK is stressful enough without having to figure out HMRC’s rules and how to fulfill your UK expat tax obligations on top of everything else. We help expats get their UK taxes sorted, so they can focus on settling in – not trying to make sense of confusing forms and deadlines.

Our network of UK and cross-border tax specialists prepares and reviews tax returns, lets you know exactly what you need to do, and makes sure everything is filed correctly and on time. We also keep an eye out for ways to reduce your UK income tax bill, so you’re not paying more than you should.

Whether you’re trying to understand how your foreign income is taxed, which deadlines apply to you, or how to fix something from a previous year, we’re here to guide you through it with UK expat tax advice.

By booking a consultation, you’ll receive a £100 credit that can be applied to any future services with your chartered tax adviser – including UK tax return preparation – so you can start saving straight away.

Book a consultation today!

DISCLAIMER: The material in this article is for general information purposes only and does not constitute legal or taxation advice. Legal, financial, investment and taxation advice should be sought before acting or refraining from acting. All information and taxation rules are subject to change without notice. Expattaxes.co.uk Limited (hereafter ‘the parties’) accept no liability for any action taken based on the information in this article or any of the articles on this website.