The Self Assessment deadline for the 2025–26 tax year depends on how you file your UK tax return. Paper returns must reach HMRC by 31 October 2026, but the deadline for online filing and tax payment is 31 January 2027. These dates relate to income earned between 6 April 2025 and 5 April 2026, not the 2026–27 tax year itself. In this guide, we shall learn which deadline applies and how it gives you time to organise your records, prepare your return and avoid late filing penalties.
What Are the UK Self Assessment Deadlines for 2026–27?
The Self Assessment deadline is entirely dependent on whether you need to register, file a paper return or submit your return online. These dates apply to the 2025–26 tax year, although HMRC may set a different filing date in certain circumstances.
| Requirement | Deadline |
| Notify HMRC or register, where required | 5 October 2026 |
| Submit a paper tax return | 31 October 2026 |
| Submit an online tax return and pay tax due | 31 January 2027 |
| Submit an online return to request payment through your PAYE tax code, if eligible | 30 December 2026 |
Check HMRC’s official Self Assessment deadlines for the latest guidance. A later notice from HMRC or specific circumstances may affect your filing date.
Paper vs Online Filing: Which Deadline Applies?
The UK tax return deadline varies on the basis of how you choose to file it. Paper returns are due in October. You get time until January if you file online instead.
Paper Filing Deadline
HMRC has set the paper tax return deadline as 31 October 2026 at 11:59 pm. Posting the return on the final day is not advised since it can arrive late, so allow time for delivery and keep proof of postage. If you miss this date, you can generally switch to online filing before the January deadline.
Online Filing Deadline
The online Self Assessment deadline is 31 January 2027, and your return must be submitted successfully by 11:59 pm. If you miss the October paper deadline, filing online by January can help you avoid a late filing penalty, provided you have not already submitted a late paper return. Sending a second return online will not normally cancel a penalty for a late paper submission.
When Must You Pay Your Self Assessment Tax?
Filing your return in October does not usually mean you have to pay your tax then. The standard payment deadline remains 31 January 2027, even if you submit your paper return months earlier.
Your bill may include the balancing payment for 2025–26, which covers tax still owed after any payments already made. If you need to make payments on account, your first instalment for the following tax year is also due on 31 January 2027. The second “payment on account” is due on 31 July 2027.
What Should You Prepare Before Filing?
Getting your records together before you start can save time when completing your tax return. Keep the following details handy so that you are not searching for missing figures close to the deadline.
- Your Unique Taxpayer Reference (UTR) and National Insurance number.
- Make sure you can access your HMRC online account before you start. It saves you from login problems at the last minute.
- Have your P60, P45 or payslips nearby if you had a job during the tax year. You may also need statements showing bank interest or dividends.
- If self-employed, keep your sales records, invoices, receipts and business expense details together. You may need to check a few figures before entering them.
- Note down any tax you have already paid, including payments on account, so you can compare it with the amount due.
- If you received other income or want to claim relief on pension contributions or charitable donations, keep those records handy too.
These records must be organised early to spot missing figures, rather than checking paperwork just before the deadline.
What Happens If You Miss a Self Assessment Deadline?
Missing a tax return deadline can lead to penalties, even if you do not owe any tax. Paying late is a separate issue and can bring additional charges.
What Are the Penalties for Late Filing and Payment?
A late Self Assessment return normally attracts an initial £100 filing penalty, even if there is no tax to pay. Further penalties can apply if the return remains outstanding, with the amount increasing as the delay continues. Late payment is treated separately. HMRC can charge interest on overdue tax and apply additional payment penalties. Check HMRC’s official penalties guidance for the current rules and charges.
What Should You Do If You Miss a Deadline?
- If your return is overdue, get it submitted as soon as you can. Waiting longer could often lead to more penalties.
- Pay the tax you owe as soon as possible. If you cannot afford the full amount, speak to HMRC about the options available.
- Missed the 5 October registration date? Contact HMRC promptly for your registration. You may be given a later filing deadline, but the payment date will generally still be 31 January.
- Appeal if you have a reasonable excuse. HMRC may consider your circumstances, so check the guidance before submitting an appeal.
Frequently Asked Questions
Can I file online if I miss the 31 October paper deadline?
Yes. You can generally submit your return online by 31 January 2027 instead. However, if you have already submitted a paper return after the deadline, filing another return online will not normally cancel the late filing penalty.
Does filing a paper return mean I must pay tax in October?
No. Filing your paper return by 31 October does not usually bring the payment deadline forward. Any tax due for the 2025–26 tax year is generally payable by 31 January 2027.
What should I do if I missed the 5 October registration deadline?
If you were supposed to register by 5 October 2026 but missed the date, get in touch with HMRC now and explain your situation. You may be given more time to file your return. The tax payment deadline, however, will generally still be 31 January 2027.
Do these deadlines cover the 2025–26 or 2026–27 tax year?
These deadlines relate to the 2025–26 tax year, which ran from 6 April 2025 to 5 April 2026. The 2026–27 tax year runs from 6 April 2026 to 5 April 2027.
Need Help Preparing Your UK Tax Return?
While filing a tax return, income records, business expenses and tax details need to be in order before filing. RNM Consulting provides UK accounting and taxation services to support businesses with record preparation and tax return requirements.
Contact RNM Consulting to discuss your accounting needs and the support available for your UK tax return today!