Most people in the UK never file a tax return. PAYE takes the right tax from wages and pensions, and that's the end of it. Self Assessment exists for everything PAYE can't reach: self-employment, rent, gains, foreign income, and the tax consequences of moving into or out of the UK.
This guide covers the 2025/26 tax year (6 April 2025 to 5 April 2026). The return is due online by 31 January 2027. If you've never filed before and need to, you must register with HMRC by 5 October 2026.
HMRC won't always know your circumstances have changed. Working out whether you need to file is your responsibility, not theirs.
What is a Self Assessment tax return?
What does a tax return actually do? It reports income and gains that haven't already been taxed correctly at source, claims any reliefs you're entitled to, and calculates the balance you owe or the refund you're due.
The main return is the SA100. You add supplementary pages for the income you have, such as SA103 for self-employment, SA105 for UK property, SA106 for foreign income, SA108 for capital gains and SA109 for residence. The last one matters for anyone who has moved into or out of the UK.
One rule overrides everything else in this guide. If HMRC sends you a notice to file, you must file by the deadline on the notice, even if you owe nothing. If you think you shouldn't be in the system, ask HMRC to withdraw the notice rather than ignoring it.
👉 HMRC guidance: Self Assessment tax returns
Who must file a UK tax return?
Who does HMRC say must file? For 2025/26, you need a return if any of the following applied in the tax year:
Self-employment: you were a sole trader with gross income over £1,000, before expenses.
Partnerships: you were a partner in a business partnership.
Capital Gains Tax: you had CGT to pay, and didn't report it through HMRC's real-time CGT service.
High Income Child Benefit Charge: you owe the charge and don't pay it through your tax code.
Off-payroll work: you're an off-payroll worker repaying a student or postgraduate loan.
You'll also usually need a return if you had untaxed income that can't be collected another way. In practice that means:
Rental income: from UK or overseas property, after the £1,000 property allowance.
Untaxed income of £2,500 or more: such as tips, commission or casual work paid gross.
Dividends over £10,000: smaller amounts above your allowances can usually go through your tax code instead.
Pension annual allowance charge: if contributions exceeded your allowance, the charge is reported on a return.
Employment expenses over £2,500: claims above this level go through Self Assessment rather than a simple claim.
👉 HMRC guidance: Who must send a tax return
Filing triggers for expats and non-residents
Why do so many internationally mobile people end up in Self Assessment? Because residence changes almost always need a return to claim the right treatment, and HMRC's PAYE system can't do it for you.
Image 1 — the common filing triggers
If you're UK resident
Foreign income or gains. Since 6 April 2025 the remittance basis has gone, so UK residents are taxed on foreign income and gains as they arise. That income goes on the return, with credit for foreign tax.
The FIG regime. New arrivals who were non-resident for 10 consecutive years can claim four years of relief on foreign income and gains, but only through the return. See our guide to the 4-year FIG regime.
The Temporary Repatriation Facility. Former remittance basis users designate old offshore income and gains on the return. See our guide to the Temporary Repatriation Facility.
Arriving part-way through the year. Split-year treatment has to be claimed on the SA109 residence pages.
Returning within five years. Coming back after a short period abroad can bring gains and some income from the non-resident years into charge. See our guide to the temporary non-residence rules.
If you're non-resident
UK rental income. You must file even if your letting agent pays you gross under the non-resident landlord scheme. Gross payment only defers the tax to the return. See our guide to the non-resident landlord scheme.
Leaving part-way through the year. Most leavers are owed a refund of PAYE, and split-year treatment is claimed on the SA109. See our guide to split-year treatment.
UK workdays. Salary for work physically done in the UK stays taxable here. See working remotely abroad for a UK company.
Selling UK property. Non-residents must report every disposal of UK land or property within 60 days, even where no tax is due, and include it on the return if they file one. See our guide to non-resident capital gains tax.
What if your only UK income as a non-resident is bank interest or dividends? That income is usually disregarded income, which caps your UK tax on it, and you won't normally need a return for it alone unless HMRC asks. See our guide to disregarded income and our overview of what the UK taxes once you've left.
👉 HMRC guidance: Tax on your UK income if you live abroad
When you don't need to file
Can you avoid Self Assessment? Several recent changes mean fewer people need a return than before:
High earners taxed only through PAYE. The old rule that PAYE earners over £100,000, and later £150,000, had to file was removed from 2024/25. If all your income is taxed through PAYE and nothing else on this page applies, you don't need a return.
High Income Child Benefit Charge. Since autumn 2025, employed people whose only reason for filing is the charge can leave Self Assessment and pay it through their tax code instead.
Small amounts of untaxed income. Below £2,500, HMRC can usually collect the tax through your tax code. Tell HMRC between the end of the tax year and 5 October.
Gains, if you're UK resident. The real-time CGT service lets you report and pay without registering for Self Assessment.
If you're already registered and no longer need to file, tell HMRC. Until you do, they'll keep issuing notices, and late filing penalties follow each one.
👉 HMRC guidance: If you no longer need to send a tax return
How to register for Self Assessment
How do you get into the system for the first time? You register with HMRC by 5 October after the end of the tax year in which you first needed to file.
For example, if you started letting a flat in May 2025, that income falls in the 2025/26 tax year, so you must register by 5 October 2026. HMRC then issues your Unique Taxpayer Reference (UTR), a ten-digit number that stays with you for life. The activation letter goes by post, so leave time if you're overseas.
Register late and you may face a failure to notify penalty if the tax isn't paid by 31 January. It's based on the tax left unpaid, so registering on time matters most when there's tax to pay.
👉 HMRC guidance: Register for Self Assessment
Non-residents without a UK address or National Insurance number often struggle with online registration. Our guide to HMRC forms for expats covers the paper route.
Self Assessment deadlines for 2025/26
Which dates actually matter? The UK tax year runs from 6 April to 5 April. For the 2025/26 year, the key dates are:
Image 2 — 2025/26 deadlines and what lateness costs
5 October 2026: register for Self Assessment if you're filing for the first time.
31 October 2026: file a paper return.
30 December 2026: file online by this date if you owe less than £3,000 and want it collected through your tax code.
31 January 2027: file online, and pay the balance for 2025/26 plus your first payment on account for 2026/27.
31 July 2027: pay your second payment on account.
Worked example: the first-year bill
Payments on account catch out most new filers. If your bill is over £1,000 and less than 80% of your tax was collected at source, HMRC asks for two advance payments towards next year, each half of this year's bill.
Sam starts letting a flat in 2025/26 and owes £4,000 on the rental profit.
On 31 January 2027 Sam pays the £4,000, plus a first payment on account of £2,000 for 2026/27.
On 31 July 2027 Sam pays a second £2,000.
That's £6,000 due in January rather than the £4,000 Sam expected. If income is falling, you can apply to reduce payments on account, but interest applies if you reduce them too far.
👉 HMRC guidance: Understand your Self Assessment tax bill
What happens if you file or pay late?
How much does missing a deadline cost? Late filing penalties are automatic and apply even if you owe no tax at all:
1 day late: a £100 penalty.
3 months late: £10 a day for up to 90 days, a maximum of £900.
6 months late: 5% of the tax due or £300, whichever is greater.
12 months late: another 5% or £300, whichever is greater.
Paying late is charged separately: 5% of the unpaid tax at 30 days, 6 months and 12 months. Interest runs on top from the day after the due date, at the Bank of England base rate plus 4%.
If you had a reasonable excuse, such as serious illness, you can appeal. It's far easier to file on time and agree a payment plan if you can't pay in full.
👉 HMRC guidance: Self Assessment penalties
Making Tax Digital: what changed from April 2026
Does Making Tax Digital affect you? From 6 April 2026, sole traders and landlords must keep digital records and send HMRC quarterly updates if their qualifying income is over the threshold. Qualifying income is gross self-employment and property income before expenses:
From April 2026: qualifying income over £50,000 on your 2024/25 return.
From April 2027: over £30,000 on your 2025/26 return.
From April 2028: over £20,000.
You still finalise the year after it ends, and other income such as salary, dividends and gains goes into that year-end submission. For jointly owned property, only your share of the rent counts towards the threshold.
Non-residents get breathing space. If you filed the SA109 residence pages for 2024/25 and expect to file them for 2026/27, you're automatically exempt until April 2027 at the earliest. Anyone without a National Insurance number is exempt too.
👉 HMRC guidance: Exemptions from Making Tax Digital for Income Tax
How to file your tax return
How do you actually submit it? If your affairs are straightforward, HMRC's free online service works well. You sign in through your personal tax account or Government Gateway.
There's one significant gap. HMRC's online service can't file the SA109 residence pages, which every non-resident and every split-year claimant needs. You can either file the whole return on paper, with the earlier 31 October deadline, or buy commercial software that supports SA109 and file online by 31 January. You can't mix the two. The third option is to have an adviser file it for you, which is what our UK tax return service for expats is for.
👉 HMRC guidance: File your Self Assessment tax return online
👉 HMRC list: Self Assessment commercial software suppliers
Keep your records. HMRC expects you to keep them for at least 22 months after the end of the tax year, or 5 years after the 31 January deadline if you're self-employed or a landlord. For cross-border returns, that includes travel records supporting your residence position.
Frequently asked questions
Do I need to file a tax return if I'm only employed?
Usually not. If all your income is taxed through PAYE, you don't need a return, whatever you earn. You'll still need one if you have other untaxed income, gains to report, or HMRC sends you a notice to file.
Do I need to file a UK tax return if I live abroad?
Often, yes. It depends on your UK income, not on where you live. You usually need to file if you have UK rental income, UK self-employment income or a UK pension that is not fully taxed, if you are reclaiming overpaid UK tax, or if you are claiming split-year treatment or non-resident status. Non-residents file the SA109 residence pages, which HMRC’s own free online service does not support.
What is the deadline to register for Self Assessment for 2025/26?
5 October 2026. You need to register by then if you're filing for the first time, or if you didn't need to file for 2024/25. HMRC will then send you a Unique Taxpayer Reference.
Do I have to file if I don't owe any tax?
Yes, if HMRC has sent you a notice to file. The £100 late filing penalty applies even when no tax is due. If you no longer need to be in Self Assessment, ask HMRC to withdraw the notice instead.
Can I file the SA109 residence pages online with HMRC?
No. HMRC's free online service doesn't support SA109. Non-residents and split-year claimants either file a paper return by 31 October or use commercial software to file online by 31 January.
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