Guides / Self Assessment deadlines
Guide
Self Assessment deadlines
Missing a Self Assessment deadline costs at least £100. This guide sets out every key date in the order you will meet it, who each one applies to, and what happens if you miss it.
7 min read · Updated October 2026 · Reviewed by qualified accountants
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In short
- Register for Self Assessment by 5 October after the end of the tax year in which you first need to file.
- File your online return by 31 January. The 2025/26 return is due by 31 January 2027.
- Pay your tax by 31 January. Payments on account fall on 31 January and 31 July.
- Paper returns must reach HMRC by 31 October.
- Filing late starts with a £100 penalty, even if you owe no tax.
How the Self Assessment tax year works
The UK tax year runs from 6 April to 5 April. Each Self Assessment return covers one complete tax year. The 2025/26 return, for example, reports income you received between 6 April 2025 and 5 April 2026.
You can file your return any time after the tax year ends on 5 April, so the 2025/26 return could have been filed from 6 April 2026. Filing early does not bring your payment date forward. Any tax you owe is still due on 31 January, so filing early simply gives you more time to plan and to find out your bill.
Key Self Assessment dates
These are the dates for the 2025/26 tax year, which is the return most people are filing now.
| Date | What happens |
|---|---|
| 5 April 2026 | The 2025/26 tax year ends |
| 6 April 2026 | You can start filing your 2025/26 return |
| 5 October 2026 | Deadline to register for Self Assessment if you have never filed before |
| 31 October 2026 | Deadline for paper returns |
| 30 December 2026 | File online by this date if you want a small underpayment collected through your PAYE tax code |
| 31 January 2027 | Online return deadline, balancing payment for 2025/26 and first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
The same pattern repeats every year, one year later.
Mark the dates now
Add 5 October, 31 January and 31 July to your calendar with a reminder two weeks before. Most penalties come from people who simply forget.
Registering for Self Assessment by 5 October
If you have not filed a return before, you must register with HMRC by 5 October after the end of the tax year in which you first had income to report. You normally need to register if you:
- started working for yourself as a sole trader or in a partnership
- began receiving rental income
- have other untaxed income, such as foreign income or large amounts of savings interest
- need to report a capital gain
HMRC sends your 10-digit Unique Taxpayer Reference (UTR) by post, and a separate activation code for your online account follows. Because both arrive by post, register as early as you can. Waiting until the deadline leaves no margin if something is delayed.
Which deadline applies to you?
Almost everyone files online, so 31 January is the date to remember. It is also the day your balancing payment and first payment on account for the next year are due.
The 31 October paper deadline only helps if you file a paper return. Paper returns are slower, give you fewer built-in checks and have to be posted to HMRC, so most people choose to file online.
There is one extra date worth knowing. If you owe less than £3,000 and you are also employed or receive a pension, you can ask HMRC to collect the tax through your PAYE tax code in the following year, as long as you file online by 30 December.
Capital gains on UK property
If you sell UK residential property and there is tax to pay, you must report the sale and pay the tax within 60 days of completion. This is separate from your Self Assessment deadline, which still applies to your full return.
Making Tax Digital
Self-employed people and landlords with qualifying income above the threshold are moving to Making Tax Digital for Income Tax, with quarterly updates and a final declaration. Read our Making Tax Digital guide to see whether you are affected.
When do you pay your tax?
Your tax bill for a tax year is due on 31 January after the year ends. Many people also have to make payments on account, which are advance payments towards the next year’s bill.
You make payments on account if your last Self Assessment bill was over £1,000 and less than 80% of your tax was collected at source. Each payment is half of your previous year’s bill and they fall on 31 January and 31 July.
A simple example
Suppose your 2025/26 bill is £4,000 and you have not made payments on account before. On 31 January 2027 you pay £4,000 for 2025/26, plus a first payment on account of £2,000 for 2026/27, so £6,000 in total. On 31 July 2027 you pay a second payment on account of £2,000. Any difference between your payments on account and your real 2026/27 bill is settled the following January.
If your income has fallen, you can ask HMRC to reduce your payments on account so you do not overpay.
What happens if you miss a deadline?
HMRC applies penalties automatically, and they build up the longer a return is outstanding.
| How late | Penalty |
|---|---|
| Day after the deadline | £100 fixed penalty, even if you owe no tax |
| 3 months late | £10 a day for up to 90 days, a maximum of £900 |
| 6 months late | 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 |
Paying late is penalised separately. Interest runs from the due date, and HMRC adds penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months. See our full late tax return penalties guide and use the penalty calculator to estimate your own position.
Already late?
File as soon as you can. Every extra day or month adds to the penalties, and we can prepare overdue returns for any tax year.
How to make sure you never miss a deadline
- Register early. Do not wait for 5 October.
- Keep records through the year. A simple monthly routine for income and expenses makes filing quick.
- File early. You can file from 6 April, and finding out your bill early lets you set money aside.
- Set reminders. Use calendar alerts for 5 October, 31 January and 31 July.
- Ask for help. If your affairs are complicated, an accountant can prepare and file the return for a fixed fee.
Written and reviewed by the Accotax tax team
Accotax is a London firm of qualified accountants and tax consultants, on the ICAEW approved employers list. Our team prepares Self Assessment, landlord and company tax returns every day, and each guide is checked against GOV.UK before it is published and updated every tax year.
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Questions, answered.
You face an automatic £100 penalty, with more added the longer the return is late. See our guide to late tax return penalties.
Payment is due by 31 January for the balancing payment, with payments on account due on 31 January and 31 July.
Yes. You can file from 6 April, straight after the tax year ends. You still have until 31 January to pay any tax due.
No. Non-resident taxpayers have the same filing and payment deadlines as everyone else, and must register by 5 October if they have UK income to report.
The deadline does not move. Your return must be filed and payment must reach HMRC by 31 January, so allow for bank processing times.
HMRC can cancel a penalty if you had a reasonable excuse, such as serious illness or a bereavement. You must file as soon as the problem is over and explain what happened.
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