The short version
Most employees on PAYE never have to do a tax return — the tax just comes off their wages. Self Assessment is for people whose income isn't fully taxed at source: the self-employed, landlords, partners, and people with extra untaxed income or the Child Benefit charge.
If you do need to file, it's free to register and file directly with HMRC, and once you're set up it's the same calm steps every year: register early, file by 31 January, pay what you owe. Miss the deadline and there's an automatic £100 penalty — so the whole game is doing it on time.
The UK tax year runs 6 April to 5 April. A Self Assessment return reports your income and works out the tax for that year. You report the year just gone — so the return for 2025/26 (year ended 5 April 2026) is filed and paid by 31 January 2027.
Do I need to file a return?
You usually need to send a Self Assessment return for a tax year if any of these applied:
You probably need to file if…
☐ You were self-employed (a sole trader) and earned more than £1,000 (the trading allowance)
☐ You were a partner in a business partnership
☐ You were a landlord with property income above the £1,000 property allowance
☐ You had to pay the High Income Child Benefit Charge (you or your partner had income over £60,000 and someone got Child Benefit)
☐ You had Capital Gains Tax to pay (e.g. selling a second property, shares or other assets)
☐ You had untaxed income not collected through PAYE — some savings interest, dividends, foreign income, tips or commission
☐ HMRC sent you a notice to file a return — you must do it (or tell HMRC if you think you don't need to)
You can claim a £1,000 trading allowance against self-employed income and a separate £1,000 property allowance against rental income — if your income from each is under those amounts, you generally don't need to report it. Above them, you usually do.
The key dates
Self Assessment runs on the same calendar every year. For a tax year ending 5 April:
| Deadline | What it's for |
|---|
| 5 October | Register for Self Assessment — by 5 October after the end of the tax year you need to report. This is the deadline to tell HMRC you need to file for the first time, so you get your UTR in time. |
| 31 October | Deadline for a paper tax return (midnight). Most people file online instead and get longer. |
| 31 January | Deadline for your online tax return and to pay the tax you owe for the year (midnight). The big one. |
| 31 July | Deadline for your second payment on account, if you make them (see below). |
Worked example — the 2025/26 return
The 2025/26 tax year ended 5 April 2026. If it's your first return, register by 5 October 2026. File the paper return by 31 October 2026, or — much more common — file online and pay any tax by 31 January 2027, with a second payment on account (if due) by 31 July 2027.
What happens if you're late
HMRC's penalties stack up the longer a return is overdue — and the first one applies even if you owe no tax or are due a refund:
| How late | Late-filing penalty |
|---|
| Missed 31 January | £100 automatic penalty, even if you owe nothing. |
| 3 months late | £10 a day for up to 90 days — up to a further £900. |
| 6 months late | A further £300 or 5% of the tax due, whichever is higher. |
| 12 months late | Another £300 or 5% of the tax due, whichever is higher (more in serious cases). |
Paying late is penalised separately. Broadly, HMRC charges a penalty of around 5% of the unpaid tax at 30 days, again at 6 months, and again at 12 months — and it charges interest on tax paid late, running daily from the day after the deadline until you pay. The exact interest rate is set as the Bank of England base rate plus a fixed margin and changes over time, so check the current rate on GOV.UK.
Can't pay, or filed late with a good reason?
If you can't pay your bill in full, don't ignore it — ask HMRC for a Time to Pay arrangement (you can often set up an instalment plan online), and you won't get further late-payment penalties as long as you stick to it.
If you missed a deadline because of something genuinely outside your control (a reasonable excuse, e.g. serious illness or a bereavement), you can appeal the penalty through your HMRC account or by post.
How payments on account work
This is the bit that surprises people in their first January. Payments on account are advance payments towards next year's tax bill. They usually apply if your Self Assessment bill is over £1,000 and less than 80% of your tax was already collected at source (for example through PAYE).
- You make two payments, each normally 50% of your previous year's bill.
- The first is due by 31 January, alongside the balancing payment for the year just gone — so that January you can be paying 1.5× a year's tax.
- The second is due by 31 July.
- The following January, the payments on account are set against your actual bill, leaving a smaller balancing payment (or a refund if you overpaid).
If you know your income has dropped, you can ask HMRC to reduce your payments on account — but don't reduce them below what you'll actually owe, or interest is charged on the shortfall.
How to register and file
If this is your first return, you register once; after that you just file each year.
- Register with HMRC — at gov.uk/register-for-self-assessment. You set up (or sign in to) a Government Gateway account and give your details, including your National Insurance number.
- Get your UTR — HMRC posts you a 10-digit Unique Taxpayer Reference, usually within about 10 working days (longer — around 21 days — if you're abroad), plus a separate activation code to switch on your online account. Because it takes time, register early.
- File online — sign in to your HMRC account and complete the return, or use commercial software. Online returns are due by 31 January (paper by 31 October).
- Pay what you owe — by 31 January, plus any payment on account. Pay online via your HMRC account; if you can't pay in full, set up a Time to Pay plan.
Keep your records
Keep records of your income and expenses — HMRC says to keep them for at least 5 years after the 31 January deadline for that return (the self-employed). Good records make the return quick and protect you if HMRC ever asks questions.
A big change: Making Tax Digital
Making Tax Digital for Income Tax — starts 6 April 2026
From 6 April 2026, the way some people do Self Assessment is changing. If your qualifying income — your total gross income (before expenses) from self-employment plus property/rental — was over £50,000 in the 2024/25 tax year, you must use Making Tax Digital (MTD) for Income Tax from 6 April 2026. (Employment and pension income don't count towards the £50,000.)
That means keeping digital records and sending quarterly updates to HMRC through compatible software, then a final declaration after the year — instead of one annual return.
The threshold then lowers in stages: it drops to over £30,000 from April 2027, and over £20,000 from April 2028. If your income is below the current threshold, you carry on filing your normal Self Assessment return as usual. Check your position on the GOV.UK MTD eligibility tool below.
Do this right now
If you think you might need to file, here's the calm, free order:
Register, file, pay — in order
- Check if you need to file. Use the free GOV.UK tool at gov.uk/check-if-you-need-tax-return.
- Register early. If it's your first return, register at gov.uk/register-for-self-assessment by 5 October so your UTR arrives in time.
- File online by 31 January. Through your HMRC account or commercial software — and pay the tax you owe the same day.
- Can't pay? Don't miss the deadline — set up a Time to Pay plan on GOV.UK or call HMRC. And check the Making Tax Digital eligibility tool if your income is over £50,000.
The HMRC Self Assessment helpline is 0300 200 3310 — busiest in January, so call early if you can.
For free, independent help: Low Incomes Tax Reform Group (LITRG) explains Self Assessment in plain English, TaxAid helps people on low incomes for free, and Citizens Advice can help if things are tangled. The HMRC Self Assessment helpline is 0300 200 3310.
Watch out for tax scams
HMRC "tax refund" or "tax owed" texts & emails are scams
Around the 31 January deadline, fake HMRC messages spike. They might say you're owed a refund, or threaten arrest over "unpaid tax", and push you to click a link or call a number — to steal your bank and personal details. HMRC never asks for bank or card details by text or email, and never threatens immediate arrest.
Do this: don't click. Forward scam texts to 60599 and scam emails to phishing@hmrc.gov.uk, then delete them. Only ever log in through gov.uk or the official HMRC app. Not sure if a message is real? Run it through Sorted's free scam check →
You don't need to pay a "tax rebate" firm
If you're owed money back through Self Assessment you keep 100% by claiming yourself through HMRC for free. Third-party "tax rebate" firms take a commission — often around a third — out of money that's already yours, and HMRC doesn't endorse any agent.