Getting to know the deadlines for filing your tax return is important for individuals and organisations in the United Kingdom. Every year, taxpayers must provide details of their income and pay any tax owed through the Self Assessment system authorised by HM Revenue and Customs. Surpassing these deadlines can lead to penalties and interest charges along with additional compliance issues.
The 2025/26 tax year starts from 6 April 2025 to 5 April 2026. As the tax year comes to an end, taxpayers need to complete a Self Assessment return. They need to submit details of their income and expenditures within the deadlines set by HMRC.
This article explains the key deadlines for the 2025/26 tax return, who must submit a return, how the process works, and what happens if the deadlines are missed.
Understanding the UK Tax Year
Before discussing the deadline, it is important to understand how the UK tax year works. Unlike many countries that follow the calendar year, the UK tax year runs from 6 April to 5 April of the following year.
For example:
- Tax Year: 6 April 2025 – 5 April 2026
- Tax Return Filing Period: Starts after 6 April 2026
- Final Online Deadline: 31 January 2027
This means that the tax return for income earned between April 2025 and April 2026 must normally be submitted by 31 January 2027 if filed online.
Understanding this timeline helps taxpayers prepare their financial records and avoid last-minute stress when the deadline approaches.
Key Deadlines for the 2025/26 Tax Return
The UK Self Assessment system has several important dates throughout the year. Missing any of these can result in penalties.
1. Register for Self Assessment – 5 October 2026
If you are filing a Self Assessment tax return for the first time, you must inform HMRC by 5 October 2026. This applies if you:
- Have never filed a Self Assessment before
- Were previously registered but did not file a return in the previous year
Once registered, HMRC will provide a Unique Taxpayer Reference (UTR) and instructions for submitting your return.
Failing to register by this date may delay the process and could lead to penalties if your return is late.
2. Paper Tax Return Deadline – 31 October 2026
If you choose to file your Self Assessment tax return using a paper form, HMRC must receive it by 31 October 2026.
Paper filing is less common today because most taxpayers use the online system. However, it may still be used by individuals who prefer manual submissions or do not have reliable internet access.
If HMRC receives your paper return after this date, it will be treated as late unless you have a valid reason.
3. Online Tax Return Deadline – 31 January 2027
For most taxpayers, the key deadline is the online submission date. If you file your return electronically, the deadline is:
11:59 pm on 31 January 2027
This is the final date to:
- Submit your Self Assessment tax return
- Pay any tax owed for the 2025/26 tax year
If you miss this deadline, HMRC may issue an automatic penalty even if you owe no tax.
Submitting early is strongly recommended so you know how much tax you owe and have time to arrange payment if necessary.
| Date notice to file issued by HMRC | Deadline for submitting paper return | Deadline for submitting return to HMRC to calculate tax (paper returns only) |
Deadline for submitting return online |
| On or before 31 July 2026 | 31 October 2026 | 31 October 2026 | 31 January 2027 |
| 1 August 2026 to 31 August 2026 | 3 months from date of notice | 31 October 2026 | 31 January 2027 |
| 1 September 2026 to 31 October 2026 | 3 months from date of notice | 2 months from date of notice | 31 January 2027 |
| After 31 October 2026 | 3 months from date of notice | 2 months from date of notice | 3 months from date of notice |
When Can You Submit the 2025/26 Tax Return?
Although the final deadline is January 2027, you do not need to wait until the last minute. Tax returns for the 2025/26 year can be submitted from 6 April 2026 onwards.
Submitting early offers several advantages:
- You know your tax bill sooner
- You have more time to arrange payment
- You avoid system delays close to the deadline
- You reduce the risk of errors or missing information
Many accountants recommend completing your return during the summer or autumn rather than waiting until January.
Who Needs to Submit a Self Assessment Tax Return?
Not everyone in the UK needs to complete a tax return. Most employees pay tax automatically through the PAYE (Pay As You Earn) system.
However, you may need to submit a Self Assessment return if you:
- Are self-employed or a sole trader
- Earn income from renting property
- Are a company director
- Have significant savings, dividends, or investment income
- Receive income from overseas
- Earn more than £1,000 from a side business or freelance work
HMRC may also request a return if they believe you owe additional tax.
Payments on Account
Some taxpayers are required to make advance payments towards the next year’s tax bill. These are known as payments on account.
If your Self Assessment bill exceeds £1,000 and most of your income is not taxed through PAYE, you may need to make two payments:
- 31 January 2027 – first payment on account
- 31 July 2027 – second payment on account
These payments are based on the previous year’s tax bill and are deducted from your final liability for the following tax year.
What Happens If You Miss the Deadline?
Missing the Self Assessment deadline can result in financial Self Assessment penalties and interest charges. The initial penalty is typically £100 if the return is filed after the deadline, even if no tax is owed.
Further penalties may apply if the delay continues:
- Daily fines after three months
- Additional penalties after six months
- Interest on unpaid tax
These charges can accumulate quickly, so it is important to submit your return and pay any tax due on time.
Tips for Completing Your Tax Return on Time
To ensure your tax return is filed before the deadline, it is important to stay organised throughout the year.
Keep Accurate Records
Maintain records of your income, expenses, and financial transactions. This makes completing the tax return much easier.
Start Early
You can begin preparing your return shortly after the tax year ends in April.
Gather Required Documents
Typical documents include:
- P60 or P45 forms
- Bank statements
- Dividend certificates
- Rental income records
- Business expense receipts
Use Online Filing
Submitting your tax return online is usually faster and more convenient than sending a paper form.
Seek Professional Advice
If your finances are complex, an accountant or tax adviser, such as Lexarox Accounts, can help ensure your return is accurate and compliant.
Future Changes to the UK Tax System
The UK government is gradually introducing Making Tax Digital (MTD) for Income Tax. This initiative aims to modernise the tax system by requiring digital record-keeping and more frequent reporting.
From April 2026, many sole traders and landlords earning over £50,000 will need to submit quarterly updates to HMRC using approved software.
However, the 2025/26 tax return will still follow the traditional Self Assessment process, with the usual January 2027 deadline.
Conclusion
The tax return for the 2025/26 tax year covers income earned between 6 April 2025 and 5 April 2026. For most taxpayers, the key deadline is 31 January 2027, which is the final date to submit the online Self Assessment return and pay any tax owed.
Important deadlines to remember include:
- 5 October 2026 – register for Self Assessment if required
- 31 October 2026 – deadline for paper tax returns
- 31 January 2027 – deadline for online tax returns and payment
Submitting your return early and keeping accurate financial records can help you avoid penalties and manage your tax obligations more efficiently.
By understanding the deadlines and preparing in advance, UK taxpayers can ensure they meet their responsibilities and stay compliant with HMRC regulations.
Frequently Asked Questions
When does the 2025/26 tax year start and end in the UK?
The 2025/26 tax year in the United Kingdom runs from 6 April 2025 to 5 April 2026. Any income earned during this period must be reported in the Self Assessment tax return for that tax year.
When is the deadline to submit the 2025/26 Self Assessment tax return?
The deadline to submit the online Self Assessment tax return for the 2025/26 tax year is 31 January 2027. If you choose to submit a paper return, the deadline is 31 October 2026.
When do I need to register for Self Assessment for the 2025/26 tax year?
If you are filing a Self Assessment tax return for the first time, you must register with HMRC by 5 October 2026. This allows HMRC to issue your Unique Taxpayer Reference (UTR) and give you access to the online filing system.
Can I submit my 2025/26 tax return before the deadline?
Yes. You can submit your Self Assessment tax return from 6 April 2026 onwards, once the tax year has ended. Filing early allows you to know your tax liability sooner and helps avoid last-minute issues.
What happens if I miss the Self Assessment deadline?
If you miss the deadline for submitting your tax return, HMRC usually charges an initial £100 penalty, even if no tax is owed. Additional penalties and interest may apply if the delay continues.
Who needs to file a Self Assessment tax return in the UK?
You may need to complete a Self Assessment return if you are self-employed, a landlord receiving rental income, a company director, or someone earning income that is not taxed through PAYE. HMRC may also require a return in certain circumstances.
Do I have to pay my tax bill at the same time as submitting my return?
Yes. Any tax owed for the 2025/26 tax year must normally be paid by 31 January 2027, which is the same deadline as the online tax return submission.
