Every year, millions of people in the UK must send a Self Assessment tax return to HMRC. If you miss a deadline, you can get a penalty, even if the mistake was small. This guide explains the key dates and penalties in simple English, so you can plan ahead and avoid extra charges.
This guide was checked on gov.uk on 6 October 2026. It covers the 2025/26 tax year (6 April 2025 to 5 April 2026). The tax return for this year is due by 31 January 2027 if you file online.
Who needs to send a tax return?
You must send a Self Assessment tax return for the 2025/26 tax year if, for example:
- you were self-employed as a sole trader and earned more than £1,000 (before taking off anything you can claim)
- you were a partner in a business partnership
- you had to pay Capital Gains Tax
- you had to pay the High Income Child Benefit Charge and do not pay it through your tax code
- HMRC wrote to you and asked you to send a return
You may also need a return if you had other untaxed income, such as rent from a property, tips, commission, savings interest, dividends or foreign income.
Self Assessment deadlines for the 2025/26 tax year
Here are the main dates you need to know:
- 5 October 2026 – deadline to register for Self Assessment if you need to send a return for the first time. If you missed it, register as soon as possible.
- 31 October 2026 – deadline for paper tax returns (by 11:59pm).
- 30 December 2026 – deadline to file online if you want HMRC to collect the tax you owe through your PAYE tax code (by 11:59pm).
- 31 January 2027 – deadline for online tax returns (by 11:59pm).
- 31 January 2027 – deadline to pay the tax you owe for 2025/26, and your first payment on account for 2026/27 if you need to make one.
- 31 July 2027 – deadline for your second payment on account for 2026/27.
Most people file online. It is quicker, and you get three more months than with a paper return.
What are payments on account?
Payments on account are advance payments towards next year’s tax bill. They are due by 31 January and 31 July. Each payment is usually half of the tax you owed for the year before.
You do not need to make payments on account if:
- your last Self Assessment tax bill was less than £1,000, or
- you already paid more than 80% of all the tax you owed, for example through your tax code
If your income goes down, you can ask HMRC to reduce your payments on account, online or with form SA303. Be careful: if you reduce them too much, you will pay interest on the difference.
Payments on account often surprise people in their second year of self-employment. In January you may have to pay the full bill for last year plus half of next year’s bill at the same time, so it is wise to save money each month.
Penalties for filing your tax return late
If your tax return is late, HMRC charges these penalties:
- 1 day late: a £100 penalty
- 3 months late: £10 for each extra day, up to a maximum of £900
- 6 months late: a further 5% of the tax due or £300, whichever is greater
- 12 months late: another 5% of the tax due or £300, whichever is greater
So a return that is a year late can cost you £1,600 or more in penalties alone, before any tax or interest.
Penalties for paying your tax late
If you file on time but do not pay on time, you will also get late payment penalties. HMRC charges 5% of the tax still unpaid at each of these points:
- 30 days after the payment deadline
- 6 months after the payment deadline
- 12 months after the payment deadline
On top of this, HMRC charges interest on tax you pay late. Since 6 April 2025, late payment interest is the Bank of England base rate plus 4%. Interest is charged every day until you pay.
If you cannot pay in full, contact HMRC before the deadline. You may be able to set up a payment plan to pay in monthly amounts.
Making Tax Digital and the new penalty system
From 6 April 2026, sole traders and landlords with qualifying income over £50,000 (based on their 2024/25 tax return) must use Making Tax Digital for Income Tax. This means sending quarterly updates through software, as well as a tax return.
For people in Making Tax Digital, a new points-based system replaces the old penalties for late tax returns. You get one point for each missed deadline. When you reach 4 points, you get a £200 penalty, and another £200 for each missed deadline after that. Late payment penalties also work differently.
But note: HMRC says the current penalties (the ones in this guide) still apply to your 2025/26 tax return due on 31 January 2027. Read our guide to Making Tax Digital for sole traders and landlords to learn more.
What if you have a reasonable excuse?
If you have a reasonable excuse for missing a deadline, you can appeal against the penalty. HMRC decides if your excuse is accepted, so keep evidence of what happened.
If you do not appeal, you must pay the penalty within 30 days of getting the penalty notice.
Simple tips to avoid penalties
- Keep all your receipts, invoices and bank statements in one place during the year.
- Do not wait until January. File your return early, for example in the summer or autumn.
- Put money aside each month for your tax bill and payments on account.
- Use an accountant who knows your type of work and reminds you of the dates.
How UK Tax Co can help
UK Tax Co prepares and files Self Assessment tax returns for sole traders, taxi and Uber drivers, CIS subcontractors, landlords and company directors all over the UK. We work online, so you can send your papers by WhatsApp or email. Our fixed price for a Self Assessment tax return is £120. If you need Making Tax Digital quarterly updates, our price is £79 per quarter.
See our Self Assessment tax return service for more details.
FAQ
When is the Self Assessment deadline for the 2025/26 tax year?
31 October 2026 for paper returns and 31 January 2027 for online returns. You must also pay any tax you owe by 31 January 2027.
How much is the penalty for a late tax return?
£100 straight away. After 3 months, £10 a day up to £900. After 6 months and again after 12 months, 5% of the tax due or £300, whichever is greater.
Can I avoid a penalty if my return is late?
You can appeal if you have a reasonable excuse, and HMRC will decide. The best way is to file and pay on time.
Do I have to make payments on account?
Not if your last tax bill was less than £1,000, or if you already paid more than 80% of your tax another way, for example through your tax code.
Does Making Tax Digital change my January 2027 penalties?
No. HMRC says the current penalties still apply to the 2025/26 tax return due on 31 January 2027. The new points system applies from the tax year you join Making Tax Digital.
This article is general guidance, not personal tax advice.
Need help? Call UK Tax Co on 020 7050 0712 or WhatsApp 07579566666.