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 penalties start the moment you miss them.
This guide covers every key Self Assessment deadline for the 2024/25 tax year (online filing deadline: 31 January 2026) and the upcoming 2025/26 tax year (deadline: 31 January 2027). We also cover what is changing in April 2026 with Making Tax Digital (MTD) for Income Tax, and what it means for sole traders and landlords earning over £50,000.
Key Takeaways
- Online deadline for 2024/25 returns: 31 January 2026
- Online deadline for 2025/26 returns: 31 January 2027
- Paper return deadlines fall three months earlier: 31 October
- Register for Self Assessment by 5 October if filing for the first time
- Late filing penalty: automatic £100, even if no tax is owed
- From April 2026, Making Tax Digital is mandatory for income over £50,000
- Always pay 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 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
Who Must File – and Who Doesn’t?
Not everyone needs to complete a Self Assessment return. HMRC may also write to you directly requesting one — if they do, you must comply even if your income falls below the standard thresholds.
The table below summarises the most common situations:
| Your Situation | Do You Need to File? |
|---|---|
| Self-employed, profit over £1,000 | Yes |
| Landlord with rental income | Yes |
| Employed only, all tax via PAYE | No (unless HMRC writes to you) |
| Director of a limited company | Usually yes |
| Earning over £100,000 | Yes |
| High Income Child Benefit (over £60,000) | Yes |
| Savings/dividend income, untaxed | Yes |
Self Assessment Deadlines for 2024/25 (Filing in 2025/26)
| Date | Action Required | Status |
|---|---|---|
| 5 October 2025 | Register for Self Assessment (first-time filers) | Passed |
| 31 October 2025 | Paper return deadline for 2024/25 | Passed |
| 30 December 2025 | Deadline to pay via PAYE tax code | Passed |
| 31 January 2026 | Online return & payment deadline for 2024/25 | Passed |
| 31 July 2026 | Second payment on account for 2025/26 | Upcoming |
Self Assessment Deadlines for 2025/26 (Filing in 2026/27)
| 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 2025/26 |
| 31 October 2026 | Paper return deadline for 2025/26 |
| 30 December 2026 | Deadline to pay via PAYE tax code (if applicable) |
| 31 January 2027 | Online return & payment deadline for 2025/26 |
| 31 July 2027 | Second payment on account for 2026/27 |
Pro Tip: Filing early, as soon as April 2026, means faster refunds if you’re owed money, and more time to budget if you owe tax. You don’t pay earlier by filing earlier; the payment deadline stays 31 January 2027.
How to Register for Self Assessment
If this is your first time filing, you must register before you can submit a return. Here is how:
- Self-employed individuals: Use form CWF1 (online via HMRC)
- Landlords and investors (non-PAYE income): Use form SA1
- You will need your National Insurance number and details of income sources
- HMRC posts your Unique Taxpayer Reference (UTR) within approximately 10 working days
- Log in via HMRC Government Gateway to file, check statements and manage payments
The Self Assessment registration deadline for the 2025/26 tax year is 5 October 2026. Missing this doesn’t remove your obligation, it just risks delaying your UTR, pushing you dangerously close to the January deadline.
Payments on Account Explained (With a Real Example)
If your Self Assessment tax bill for the previous year was over £1,000, HMRC requires you to make advance payments towards next year’s bill. These are called payments on account.
They are split into two equal instalments:
- First payment on account: 31 January (same day as your main bill)
- Second payment on account: 31 July
Worked Example: Sarah, Freelance Graphic Designer
Sarah’s Self Assessment tax bill for 2024/25 is £3,200.
Because this is over £1,000, HMRC requires payments on account for 2025/26:
- Each payment = 50% of £3,200 = £1,600
- 31 January 2026: She pays her £3,200 bill PLUS £1,600 first payment on account = £4,800 total
- 31 July 2026: She pays the second payment on account = £1,600
If her actual 2025/26 tax bill turns out to be £3,600, she pays the £400 balance on 31 January 2027. If it’s lower, HMRC refunds the difference.
Tip: If your income drops significantly, you can apply to reduce your payments on account through your HMRC online account.
Self Assessment Late Filing Penalties
HMRC penalties are automatic and escalate the longer your return remains outstanding:
| How Late | Penalty |
|---|---|
| 1 day late | Automatic £100, even if no tax is owed |
| 3 months late | £10 per day for up to 90 days (max £900) |
| 6 months late | Further £300 or 5% of tax due, whichever is higher |
| 12 months late | Another £300 or 5% of tax due, whichever is higher |
In addition to filing penalties, HMRC charges separate late payment penalties:
| How Late (Payment) | Penalty |
|---|---|
| 30 days late | 5% of tax unpaid |
| 6 months late | Further 5% of tax unpaid |
| 12 months late | Another 5% of tax unpaid |
| Any unpaid balance | Daily interest charged from 1 February |
If you cannot pay in full, HMRC’s Time to Pay arrangement lets you spread payments. You must contact HMRC proactively, ideally before the deadline. You can set this up online if you owe less than £30,000.
Common Self Assessment Mistakes to Avoid
At Outbooks, these are the mistakes we see most often when clients come to us after missing a deadline or receiving an unexpected penalty:
- Forgetting the July payment on account. Many people pay the January bill but miss the 31 July second payment, triggering an immediate 5% penalty.
- Not registering early enough. Waiting until December to register means your UTR may not arrive before the January deadline.
- Claiming wrong expenses. Dual-use items (like a home phone used partly for work) require careful apportionment. Overclaiming triggers HMRC enquiries.
- Missing rental income. Landlords often forget to include income from informal arrangements or short-term lets (e.g. Airbnb).
- Ignoring Making Tax Digital. If your income is above £50,000, you must switch to MTD-compatible software from April 2026, the standard annual return will no longer be accepted.
Self Assessment Tax Refund: Could You Be Owed Money Back?
Not every return results in a bill. Many filers are entitled to a 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 processed within a few weeks of filing and paid directly to your bank account. Filing early, as soon as April 2026, means any refund arrives months sooner than if you wait until January.
Making Tax Digital for Income Tax 2026: What You Must Do Now
From 6 April 2026, Making Tax Digital (MTD) for Income Tax becomes mandatory for anyone with qualifying income over £50,000 from self-employment or property. The £30,000 threshold follows in April 2027.
This is a fundamental change to how you report income to HMRC. Instead of one annual return, you will submit:
- Quarterly updates via HMRC-approved software (4 times a year)
- Digital records of all income and expenses throughout the year
- A Final Declaration (replacing the traditional return) by 31 January after the tax year ends
MTD 2026 Checklist – What to Do Before April 2026
- Check if your qualifying income (self-employment + property) exceeds £50,000
- Choose MTD-compatible software (e.g. QuickBooks, FreeAgent, Xero, Sage)
- Sign up for MTD for Income Tax via HMRC’s Government Gateway
- Start keeping digital records of income and expenses from 6 April 2026
- Submit your first quarterly update by 7 August 2026
- Submit your MTD Final Declaration by 31 January 2028 (for 2026/27 tax year)
MTD Key Dates for 2026/27
| Date | MTD Action Required |
|---|---|
| 6 April 2026 | MTD mandatory for income over £50,000 |
| 7 August 2026 | First quarterly update deadline (Q1: Apr–Jun 2026) |
| 7 November 2026 | Second quarterly update (Q2: Jul–Sep 2026) |
| 7 February 2027 | Third quarterly update (Q3: Oct–Dec 2026) |
| 7 May 2027 | Fourth quarterly update (Q4: Jan–Mar 2027) |
| 31 January 2028 | MTD Final Declaration for 2026/27 |
| April 2027 | MTD extended to income over £30,000 |
Important: If your income is currently below £50,000, the standard Self Assessment process continues for now. However, it is worth setting up digital record-keeping now to make the transition easier when the threshold drops to £30,000 in April 2027.
How to File Your Self Assessment Tax Return Online
Filing via HMRC’s Government Gateway is straightforward once you have your UTR and login credentials:
- Log in at gov.uk/log-in-file-self-assessment-tax-return
- 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 deadline
You can file from 6 April 2026 for the 2025/26 tax year. There is no benefit to waiting, filing early means you know your position and can plan cash flow, or receive a refund sooner.
All Key Dates at a Glance
2024/25 Tax Year
| Date | Action |
|---|---|
| 5 Oct 2025 | Registration deadline (passed) |
| 31 Oct 2025 | Paper return deadline (passed) |
| 30 Dec 2025 | Deadline to pay via PAYE code (passed) |
| 31 Jan 2026 | Online return & payment deadline (passed) |
| 31 Jul 2026 | Second payment on account (upcoming) |
2025/26 Tax Year
| Date | Action |
|---|---|
| 6 Apr 2026 | Filing window opens for 2025/26 returns |
| 5 Oct 2026 | Registration deadline |
| 31 Oct 2026 | Paper return deadline |
| 30 Dec 2026 | Deadline to pay via PAYE code |
| 31 Jan 2027 | Online return & payment deadline |
| 31 Jul 2027 | Second payment on account |
2026/27 Tax Year (MTD Transition Year)
| Date | Action |
|---|---|
| 6 Apr 2026 | MTD mandatory for income over £50,000 |
| 7 Aug 2026 | First MTD quarterly update |
| 5 Oct 2027 | Registration deadline for 2026/27 |
| 31 Oct 2027 | Paper return deadline |
| 31 Jan 2028 | Online return, payment & MTD Final Declaration |
| Apr 2027 | MTD extended to income over £30,000 |
Frequently Asked Questions
When is the online Self Assessment deadline for 2026?
The online Self Assessment deadline for the 2024/25 tax year was 31 January 2026. For the 2025/26 tax year, the online deadline is 31 January 2027.
What happens if I miss the Self Assessment deadline?
HMRC charges an automatic £100 penalty even if no tax is owed. Additional daily penalties of £10 per day apply after 3 months, and further charges at 6 and 12 months. Interest is also charged on any unpaid tax from 1 February.
What is my Unique Taxpayer Reference (UTR)?
Your UTR is a 10-digit reference number HMRC assigns when you register for Self Assessment. It is required to log in and file your return. HMRC sends it by post within approximately 10 working days of registration.
What are payments on account?
Payments on account are advance payments towards next year’s tax bill. They apply if your previous bill exceeded £1,000. Each payment is 50% of your previous bill, due on 31 January and 31 July.
What expenses can I claim on my Self Assessment?
Allowable expenses include office costs, travel (excluding commuting), equipment, marketing, professional subscriptions, accountancy fees, and a portion of home costs if you work from home. You cannot claim personal expenses or the purchase of capital assets (these use capital allowances instead).
What is Making Tax Digital (MTD) and does it affect me?
MTD for Income Tax is mandatory from 6 April 2026 for sole traders and landlords with qualifying income over £50,000. It requires quarterly reporting via approved software instead of a single annual return. The threshold drops to £30,000 in April 2027.
Can I still file a paper tax return?
Yes, but the paper deadline is 31 October, three months earlier than the online deadline of 31 January. Over 97% of returns are now filed online.
How do I reduce my payments on account?
If you expect your income to be lower than the previous year, you can apply to reduce your payments on account through your HMRC online account. You must be able to justify the reduction, overclaiming can lead to interest charges.
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.