If you need to complete a self assessment tax return, one thing is certain: missing a deadline is costly. Whether you are self employed, a landlord, a company director, or someone with untaxed income, HMRC operates on strict fixed dates and the penalties for missing them start immediately.
This guide covers every key self assessment tax return deadline for both the 2024/25 tax year (filing in 2025/26) and the upcoming 2025/26 tax year (filing in 2026/27), so you can plan ahead with confidence. We also look at what is changing in 2026/27 with Making Tax Digital (MTD), which will affect thousands of sole traders and landlords.
Key Takeaways
- Self assessment deadline for 2024/25 online returns: 31 January 2026
- Self assessment deadline for 2025/26 online returns: 31 January 2027
- Paper return deadlines fall on 31 October – three months earlier than online filing
- Register for self assessment by 5 October if it is your first time filing for that tax year
- Late filing penalties start at an automatic £100 – even if no tax is owed
- Self assessment tax return deadline dates are the same each year: 31 October (paper) and 31 January (online)
- From April 2026, Making Tax Digital changes reporting for those earning over £50,000
- Always pay self assessment tax by 31 January to avoid daily interest charges.
What Is a Self Assessment Tax Return?
A self assessment tax return is how individuals report income to HMRC that has not been taxed automatically through PAYE. You may need to file a tax return if you are:
- Self-employed as a sole trader earning over £1,000
- A partner in a business partnership
- A landlord receiving rental income
- Earning over £100,000 per year
- Receiving untaxed income from savings, dividends, or foreign sources
- A company director with additional income outside PAYE
Not sure whether you need to file? Our guide on who needs to do self assessment explains the self assessment criteria in full. HMRC may also write to you directly requesting a return. If so, you must comply even if you do not meet the standard thresholds.
Self Assessment Deadlines for 2024/25 (Filing in 2025/26)
The 2024/25 tax year ran from 6 April 2024 to 5 April 2025. Here are all the key self assessment dates for this filing cycle:
| Date | Action Required |
| 5 October 2025 | Deadline to register for self assessment if filing for 2024/25 for the first time |
| 31 October 2025 | Paper self assessment tax return deadline for 2024/25 |
| 31 January 2026 | Online self assessment tax return deadline for 2024/25 |
| 31 January 2026 | Deadline to pay any tax owed for 2024/25 (balancing payment) |
| 31 January 2026 | First payment on account due for 2025/26 (if applicable) |
| 31 July 2026 | Second payment on account due for 2025/26 (if applicable) |
The hmrc tax return deadline of 31 January is the most critical date for the majority of taxpayers. Filing online gives you an extra three months compared to the paper route making the self assessment tax return login via your Government Gateway account the preferred option for most people.
Self Assessment Deadlines for 2025/26 (Filing in 2026/27)
The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Below are the upcoming self assessment tax return dates to plan for well in advance:
| Date | Action Required |
| 6 April 2026 | Filing window opens – you can submit your 2025/26 return from this date |
| 5 October 2026 | Deadline to register for self assessment for the 2025/26 tax year |
| 31 October 2026 | Paper self assessment tax return deadline for 2025/26 |
| 31 January 2027 | Online self assessment tax return deadline for 2025/26 |
| 31 January 2027 | Deadline to pay tax owed for 2025/26 (balancing payment) |
| 31 January 2027 | First payment on account due for 2026/27 (if applicable) |
| 31 July 2027 | Second payment on account due for 2026/27 (if applicable) |
The deadline for self assessment tax return follows the same annual pattern. The online deadline is always 31 January following the end of the tax year, giving you around nine months after the tax year closes to submit your self assessment form. Do not wait until January; filing early after 6 April means faster refunds and more time to budget for your bill.
How to Register for Self Assessment
If this is your first time filing, you must register for self assessment before you can submit a return. Completing the register for self assessment form is straightforward:
- Self-employed individuals use a CWF1 form
- Those with non-PAYE income (landlords, investors) use an SA1 form
- You will need your National Insurance number and details of your income sources
- HMRC posts your Unique Taxpayer Reference (UTR) within approximately 10 working days
The self assessment tax registration deadline for the 2025/26 tax year is 5 October 2026. Missing this date does not remove your filing obligation, it simply risks delays in receiving your UTR, potentially pushing you towards the January deadline unprepared.
Once registered, use the hmrc self assessment login via Government Gateway to file your return, check your tax statement and manage upcoming payments.
When Do You Start Paying Tax?
A common question for new filers: when do you start paying tax? Once you submit your self assessment return, HMRC calculates what you owe after deducting your Personal Allowance (£12,570 for both 2025/26 and 2026/27).
When do you start paying tax in UK under self assessment specifically? As soon as your taxable income (after allowances and deductible expenses) exceeds the Personal Allowance threshold. For self-employed individuals, this includes profit from your business, not just revenue.
If your previous year’s tax bill was over £1,000, you will also need to make payments on account, two advance payments towards next year’s bill. Understanding when do i have to pay tax and planning for these payments is essential to managing your cash flow effectively throughout the year.
Self Assessment Late Filing Penalties: What You Will Be Charged?
HMRC penalties for late filing are automatic and escalate the longer your return remains outstanding. Here is exactly what happens if you miss the self assessment tax return filing deadline:
| Date | Action Required |
| 1 day late | Automatic £100 penalty, even if no tax is owed and even if you have nothing to pay |
| 3 months late | £10 per day for up to 90 days (up to a maximum of £900 in additional penalties) |
| 6 months late | A further £300 or 5% of the tax due, whichever is the higher amount |
| 12 months late | Another £300 or 5% of tax due, whichever is higher; in serious cases, penalties can be significantly more |
On top of self assessment late filing penalties, HMRC also charges daily interest on any unpaid tax from the day after the self assessment tax return payment deadline. If you genuinely cannot pay in full, HMRC’s Time to Pay arrangement allows you to spread payments over monthly instalments, but you must contact HMRC proactively before or shortly after the deadline.
If illness, bereavement, or another serious event caused you to miss the self Assessment tax return deadline, you can appeal. HMRC will review your case but requires supporting evidence. File and pay self assessment tax as soon as possible regardless, to limit ongoing daily charges.
Self Assessment Tax Refund: Could You Be Owed Money Back?
Not every self assessment tax return results in a bill. Many filers are entitled to a self assessment tax refund, particularly if they:
- Overpaid tax through PAYE during the year
- Made pension contributions or Gift Aid donations
- Had significant allowable business expenses that reduced taxable profit
- Underclaimed reliefs or allowances in a previous return
Refunds are generally processed within a few weeks of filing and paid directly to your bank account. Filing your self employment tax returns early, as soon as the tax year ends, means you receive any refund far sooner rather than waiting months after the January rush.
What Is Changing in 2026/27: Making Tax Digital for Income Tax?
The 2026/27 tax year introduces a significant shift for many self employment tax returns filers. Making Tax Digital (MTD) for Income Tax becomes mandatory from 6 April 2026 for anyone with qualifying income over £50,000 from self-employment or property.
Under MTD, the traditional annual return is replaced with a new quarterly reporting system:
- Quarterly updates must be submitted via HMRC-approved software (first quarterly deadline: 7 August 2026)
- Fully digital record-keeping is required throughout the tax year
- A Final Declaration replaces the traditional return, due 31 January 2028 for the 2026/27 tax year
- The £50,000 income threshold drops to £30,000 in April 2027
Crucially, the standard self assessment tax return deadline of 31 January 2027 still applies for the 2025/26 tax year, even for those transitioning to MTD. The personal allowance remains £12,570 for 2026/27, though dividend tax rates are set to increase for basic and higher rate taxpayers.
If your income is below £50,000, you continue on the standard self assessment form process for now. However, it is worth preparing your digital record-keeping systems early to ease the transition when MTD thresholds extend to cover your income level.
How to File Your Self Assessment Tax Return Online?
Wondering how to do tax return online? The process through the HMRC portal is straightforward once you have your UTR and Government Gateway credentials. Here is a summary of how do you do a tax return online:
- Log in via the hmrc self assessment login on the Government Gateway
- Select the relevant tax year and confirm your personal details
- Enter income from all sources: employment, self-employment, rental income, savings, dividends
- Add allowable expenses and any pension or Gift Aid contributions
- Review your calculated tax bill before submitting
- Submit and pay any tax owed by the self assessment tax return deadline
You can file your self assessment tax return online from 6 April onwards, there is no need to wait until autumn. Filing early gives you a clear picture of what you owe and more time to budget, or to claim a refund if you have overpaid.
All Key Dates at a Glance
2024/25 Tax Year — Current Deadlines:
| Date | Action Required |
| 5 October 2025 | Registration deadline for 2024/25 (passed) |
| 31 October 2025 | Paper return deadline (passed) |
| 31 January 2026 | Online return & payment deadline |
| 31 July 2026 | Second payment on account |
2025/26 Tax Year – Upcoming Deadlines
| Date | Action Required |
| 6 April 2026 | Filing window opens for 2025/26 returns |
| 5 October 2026 | Registration deadline for 2025/26 |
| 31 October 2026 | Paper return deadline for 2025/26 |
| 31 January 2027 | Online return & payment deadline for 2025/26 |
| 31 July 2027 | Second payment on account for 2026/27 |
2026/27 Tax Year – Key Dates (MTD Transition Year)
| Date | Action Required |
| 6 April 2026 | MTD for Income Tax mandatory for income over £50,000 |
| 7 August 2026 | First MTD quarterly update deadline |
| 5 October 2027 | Registration deadline for 2026/27 |
| 31 October 2027 | Paper return deadline for 2026/27 |
| 31 January 2028 | Online return, payment deadline & MTD Final Declaration |
Staying on top of your self assessment dates and planning around them is the single most effective way to avoid unnecessary HMRC penalties. Whether you are a first-time filer who needs to register for self assessment, a self employed sole trader preparing for Making Tax Digital, or someone simply checking when submit tax return for the first time, getting organised early makes everything easier.
If you need help completing your self assessment tax return or are unsure about the deadline for submitting self assessment tax return that applies to your situation, speak to a qualified accountant. They can guide you through the process, ensure your return is accurate and help you avoid the stress of last-minute filing.
Conclusion
Staying ahead of your Self Assessment deadlines is the simplest way to avoid unnecessary penalties, interest and last minute stress. The key dates remain consistent each year, which means early preparation, accurate records and timely filing give you complete control over your tax position. Filing sooner also helps you plan cash flow properly and receive any refunds without delay.
With Making Tax Digital starting from April 2026 for higher earning sole traders and landlords, strong digital record keeping will soon become essential. Preparing now will make the transition smoother and reduce compliance risks.
If you need support with your Self Assessment return, Outbooks UK can help ensure everything is filed accurately and on time, so you stay compliant and focused on running your business.
Call us today on +44 330 057 8597 or email info@outbooks.co.uk to get expert help with your Self Assessment.
Frequently Asked Questions
When is the online Self Assessment tax return deadline for 2026?
The online Self Assessment tax return deadline for the 2024–25 tax year is 31 January 2026.
What happens if I miss the Self Assessment deadline?
If you miss the deadline, HMRC charges an automatic £100 penalty, even if no tax is owed. Additional penalties and interest apply the longer the return remains unfiled or unpaid.
Can I still file a paper tax return?
Yes, but the paper tax return deadline is earlier. For the 2024–25 tax year, paper returns must be submitted by 31 October 2025.
When do I need to register for Self Assessment?
If you are newly self-employed or start earning untaxed income, you must register for Self Assessment by 5 October following the end of the tax year.
What are payments on account?
Payments on account are advance payments towards your next tax bill. They usually apply if your previous year’s tax bill was more than £1,000 and are due on 31 January and 31 July.
What is the deadline for the next tax year?
For income earned during the 2025–26 tax year, the Self Assessment deadline will be 31 January 2027.
Parul is a content specialist with expertise in accounting and bookkeeping. Her writing covers a wide range of accounting topics such as payroll, financial reporting and more. Her content is well-researched and she has a strong understanding of accounting terms and industry-specific terminologies. As a subject matter expert, she simplifies complex concepts into clear, practical insights, helping businesses with accurate tips and solutions to make informed decisions.