How to File Your UK Tax Return: Self Assessment Guide (2026/27)
Llandora·Updated 2026-10-14
⚠️ Disclaimer: For general information only — not tax, financial, legal, or medical advice. Figures may be outdated or incorrect; tax rules change frequently. Verify important decisions with the CRA/IRS or a qualified professional (for health topics, a licensed healthcare provider). You use this information at your own risk.
The short answer
Most UK employees never file a tax return — tax is collected automatically through PAYE (Pay As You Earn) on each payslip. You must file a Self Assessment return if you are self-employed with turnover above £1,000, a company director, a landlord, have untaxed income or capital gains, or need to pay the High Income Child Benefit Charge. Register by 5 October following the tax year, file online by 31 January, and pay what you owe by 31 January.
Who must file
For the tax year 6 April to 5 April, you must send a return if any of these applied:
You were self-employed as a sole trader and earned more than £1,000 (before expenses).
You were a partner in a business partnership.
You had Capital Gains Tax to pay (for example, selling shares, crypto, or a second property above the annual exempt amount of £3,000).
You need to pay the High Income Child Benefit Charge (you or your partner claimed Child Benefit and either of you earned over £60,000).
You received untaxed income over £2,500 — for example, rental income or foreign income.
You are a company director, a trustee, or have income from abroad that needs UK tax paid on it.
HMRC sent you a notice to file — you must comply even if none of the above apply.
One big change: from the 2024/25 tax year, there is no income-level trigger for people taxed only through PAYE. A salaried employee earning £200,000 with no other income no longer has to file purely because of the salary. If HMRC thinks you no longer need to file, tell them online so they stop expecting a return.
Step 1: register (by 5 October)
If you have never filed before, register for Self Assessment online with HMRC. You will receive a Unique Taxpayer Reference (UTR) by post (allow about 10 working days, longer from overseas) and then set up a Government Gateway account — your login for filing, checking your tax account, and paying. The registration deadline is 5 October following the end of the tax year you need to file for. Miss it and you may face penalties even before the filing deadline arrives.
Step 2: gather your documents
Before you start, collect: P60 (year-end summary from your employer) and any P45s; payslips; bank and savings interest statements; dividend vouchers; rental income and expense records; records of self-employment income and allowable expenses; details of capital gains (purchase and sale prices, dates); pension contribution statements; and Gift Aid donation records. Self-employed records must be kept for at least 5 years after the 31 January filing deadline.
Step 3: file the return
Paper returns: deadline 31 October after the tax year ends. Almost nobody does this now.
Online returns: deadline 31 January. The HMRC online service and the HMRC app walk you through each section; most first-time filers finish in 1–2 hours.
Declare everything in the right boxes — employment, self-employment, property, savings, dividends, gains, and foreign income each have their own section. The system calculates your bill, but you are responsible for the figures.
Simple Assessment: if your affairs are straightforward (for example, you owe tax on savings interest or have underpaid PAYE), HMRC may send a Simple Assessment letter calculating the bill for you instead of requiring a return.
Step 4: pay your bill
Payment is due by 31 January — the same date as the online filing deadline. If you owe more than £1,000, you will usually also make payments on account: two advance payments toward next year's bill, each 50% of the current bill, due 31 January and 31 July. Ways to pay include bank transfer (Faster Payments), debit card online, Direct Debit, or at your bank or building society. HMRC does not accept personal credit cards. Interest accrues from 1 February on anything unpaid, so file early enough to arrange payment.
Penalties for missing deadlines
£100 immediately, even one day late.
After 3 months: £10 per day for up to 90 days (max £900).
After 6 months: a further 5% of the tax due (or £300, whichever is greater).
After 12 months: another 5% (or £300, whichever is greater).
Interest on late payment runs on top. These apply even if you owe no tax — file on time or file a nil return.
Newcomer notes
In your first UK tax year, check whether split year treatment applies (see our residency guide) — it changes which income goes on the return. If you arrive mid-year and start work, your employer puts you on an emergency tax code until HMRC issues the correct one; overpaid tax is reclaimed through your return or an in-year claim. Keep every document from day one: P45s, tenancy agreements, and arrival-date evidence all matter.
Frequently asked questions
I am employed and my tax looks right. Do I need to do anything?
No. PAYE handles it. You only need Self Assessment if one of the triggers above applies or HMRC sends you a notice to file.
What is a UTR and how long does it take?
Your Unique Taxpayer Reference is a 10-digit number HMRC uses to identify your tax account. It arrives by post, typically within 10 working days of registering (allow more if you are abroad). You cannot file without it.
Can I pay in instalments?
Yes — if you owe less than £30,000 you can usually set up a Time to Pay arrangement or pay through your tax code. Contact HMRC before the deadline; penalties still apply to late amounts not covered by an agreement.
I made a mistake on a filed return. What now?
You can amend an online return within 12 months of the 31 January deadline (so for 2025/26, until 31 January 2028). After that, write to HMRC — overpaid tax can generally be reclaimed for up to 4 years.
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