Learn › Filing your tax return in United Kingdom

In short: Most UK employees and pensioners don’t file a tax return because PAYE already collects their tax. You file a Self Assessment return if you have untaxed income — self-employment, rental, large savings/dividends, foreign income, or a high salary. Online returns are due by 31 January after the tax year ends (5 April); paper returns by the earlier 31 October. You’ll need a UTR and a Government Gateway account. Figures here are as of 2026 — check the official source when in doubt.

Filing your tax return in United Kingdom

Kontoo editorial team · Updated 06/24/2026

In the United Kingdom, most employees and pensioners never file a tax return at all — their Income Tax is collected automatically through PAYE (Pay As You Earn) by their employer or pension provider. You only need to deal with HM Revenue & Customs (HMRC) directly through “Self Assessment” if you have income that isn’t taxed at source: self-employment, rental income, large amounts of savings or dividend income, foreign income, or a high salary. This lesson explains how Self Assessment works, the key dates, and the accounts and reference numbers you’ll need. It’s general education, not personal tax advice.

Check whether you need to file at all. If all your income is from one job or pension and tax is already taken via PAYE, you usually don’t. You typically must file if you were self-employed earning over £1,000, had untaxed income (rent, savings, dividends, foreign income), or hit certain high-income thresholds. Use the official “Check if you need to send a Self Assessment tax return” tool on GOV.UK when in doubt.
Register with HMRC if it’s your first time. You’ll need to register for Self Assessment, after which HMRC issues your UTR (Unique Taxpayer Reference) — a 10-digit number — usually by post within about 10 working days. The registration deadline is 5 October after the end of the tax year. You’ll also set up or use a Government Gateway account to sign in online.
Gather your figures and complete the return. The UK tax year runs 6 April to 5 April. Collect records of income and allowable expenses, your P60/P45 if employed, and bank or dividend statements. File online through your Government Gateway sign-in, or on a paper form (SA100) if you prefer.
File and pay before the deadline. For an online return the deadline is 31 January following the end of the tax year; for a paper return it’s the earlier 31 October. Any tax you owe is also due by 31 January. Keep your records in case HMRC asks questions later.

What matters

The United Kingdom runs two parallel systems for collecting Income Tax, and which one applies to you decides whether you ever touch a tax return. The first is PAYE — Pay As You Earn. If you’re an employee or you draw a pension, your employer or pension provider deducts Income Tax and National Insurance before you’re paid and sends it to HMRC. Your tax code tells them how much to take. For millions of people this is the whole story: the right amount is collected automatically and no return is needed. The second system is Self Assessment, used for income that PAYE can’t reach. You generally need to file a Self Assessment return if, in the tax year (6 April to 5 April), you were self-employed with turnover above £1,000, received rental income, had significant untaxed savings or dividend income, earned foreign income, or had a high salary above certain thresholds. The definitive test is the “Check if you need to send a Self Assessment tax return” tool on GOV.UK — it walks through your circumstances and tells you yes or no. If you do need to file for the first time, you register with HMRC. After registering, HMRC issues your UTR (Unique Taxpayer Reference), a 10-digit number, typically posted within about 10 working days — so don’t leave registration to the last minute. The registration deadline is 5 October after the end of the relevant tax year. To file online you sign in through a Government Gateway account, the single login HMRC uses across its online services. The deadlines are the part people most often get wrong. For a given tax year ending 5 April, a paper return (form SA100) must reach HMRC by 31 October that year. An online return has the later deadline of 31 January the following year. Crucially, payment of any tax owed is due by 31 January regardless of how you filed. Miss the filing deadline and you face an automatic £100 penalty even if you owe nothing; further penalties build up the longer you leave it. All figures and rules here are current as of 2026 — always confirm your own dates and obligations on the official GOV.UK pages, and remember this is general information, not tax advice.

ExampleSuppose you have a £40,000 salary taxed under PAYE, plus £6,000 of profit from freelance work on the side in the 2025/26 tax year. The salary’s tax is already handled by your employer. On the £6,000 freelance profit, with your Personal Allowance (£12,570, as of 2026) already used up by your salary, you’d pay Income Tax at the basic rate of 20%: £6,000 × 20% = £1,200, plus any National Insurance due. Setting aside roughly £100 a month across the year would cover that £1,200 bill by the 31 January deadline. Rounded illustration only — check the official rates for your year.

Use the Kontoo budget planner to set aside a monthly amount for your tax bill so 31 January doesn’t catch you short, and check the official portal at gov.uk/self-assessment-tax-returns for your exact dates and circumstances.

In depth

PAYE and your tax code

PAYE relies on your tax code to deduct the right amount each payday. If your code is wrong — after changing jobs, having two jobs, or getting taxable benefits — too much or too little tax can be collected. HMRC may reconcile this after year-end, but it’s worth checking your code on your payslip or in your Personal Tax Account so surprises don’t pile up.

Penalties and paying late

Late filing starts at a fixed £100, then adds daily penalties after three months and percentage-based charges after six and twelve months. Paying late attracts separate penalties plus interest on the outstanding amount. If you genuinely can’t pay in full by 31 January, HMRC offers “Time to Pay” arrangements — acting early and contacting them is far cheaper than ignoring the bill.

Records and the tax year

The UK tax year is 6 April to 5 April, which trips up people used to a calendar year. Keep records of income, expenses, and supporting documents (P60, P45, bank and dividend statements) for several years, as HMRC can open enquiries after you’ve filed. Good record-keeping also makes the return itself far quicker to complete.

Checklist

Is all my income already taxed through PAYE, or do I have untaxed income that needs a Self Assessment return?
Have I registered for Self Assessment and received my UTR (allow about 10 working days, register by 5 October)?
Do I know which deadline applies — 31 October for paper, 31 January for online — and is any tax I owe set aside for 31 January?
Can I sign in to my Government Gateway account, and are my income and expense records ready?

Common myths

Myth: Everyone in the UK has to file a tax return.

Reality: No. Most employees and pensioners are taxed automatically through PAYE and never file. Self Assessment is only for people with untaxed income or other specific circumstances.

Myth: If I owe no tax, a late return is harmless.

Reality: Not so. Missing the filing deadline triggers an automatic £100 penalty even when your tax bill is zero, with further charges the longer it stays unfiled. File on time regardless.

Sources

Frequently asked questions

Do I need to file a tax return if I only have a salary?

Usually not. If you’re employed and all your tax is collected through PAYE, HMRC normally doesn’t need a Self Assessment return from you. You typically only need one if you have other untaxed income or meet specific criteria — the GOV.UK checker confirms your situation.

What’s the difference between the 31 October and 31 January deadlines?

They are two ways to file the same return. 31 October (after the 5 April year-end) is the deadline for paper returns; 31 January is the later deadline for filing online. Most people file online. Either way, any tax owed is due by 31 January. As of 2026, check gov.uk for the precise dates for your tax year.

What is a UTR and where do I get it?

A UTR (Unique Taxpayer Reference) is a 10-digit number that identifies you to HMRC for Self Assessment. You receive it after registering — usually by post within about 10 working days. You sign in to file using a Government Gateway account.

All lessons · Glossary · Editorial · Kontoo does the math and explains – this is general education, not tax, legal or financial advice.

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