Self-Assessment Tax Return Deadlines 2025/26 — Key Dates You Must Know
Self-Assessment Tax Return Deadlines 2025/26 — Key Dates You Must Know
Missing a self-assessment tax return deadline can cost you hundreds — even thousands — of pounds in penalties. Whether you're filing for the first time or you've done it every year, knowing the exact dates for the 2025/26 tax year is essential.
This guide covers every deadline you need to know, what happens if you're late, and how to make sure you never miss a filing date again.
What is the 2025/26 tax year?
The UK tax year doesn't follow the calendar year. The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Any income you earn, expenses you claim, and tax you owe during this period will be reported on your 2025/26 self-assessment tax return.
Even though the tax year ends in April 2026, you have several months after that to actually file your return and pay what you owe. But there are strict deadlines — and penalties start from day one if you miss them.
Key deadlines at a glance
Here are all the important dates for the 2025/26 self-assessment tax return:
| Date | What happens |
|---|---|
| 6 April 2025 | Start of the 2025/26 tax year |
| 5 April 2026 | End of the 2025/26 tax year |
| 6 April 2026 | Earliest you can file your 2025/26 tax return |
| 5 October 2026 | Deadline to register for self-assessment (if you're new) |
| 31 October 2026 | Deadline for paper tax returns |
| 30 December 2026 | Deadline to file online if you want HMRC to collect tax through your PAYE tax code (for amounts under £3,000) |
| 31 January 2027 | Deadline for online tax returns AND payment of tax owed (including first payment on account) |
| 31 July 2027 | Second payment on account due |
Understanding each deadline in detail
5 October 2026 — Register for self-assessment
If this is the first year you need to file a self-assessment tax return, you must register with HMRC by 5 October 2026. This applies if you:
- Became self-employed or a sole trader during 2025/26
- Earned more than £1,000 from self-employment
- Received rental income from property
- Had income from abroad
- Earned more than £150,000 in total income
- Need to pay Capital Gains Tax
- Are a partner in a business partnership
- Received income from a trust
When you register, HMRC will send you a Unique Taxpayer Reference (UTR) number by post. This can take up to 10 working days (or longer if you're overseas), so don't leave it to the last minute.
31 October 2026 — Paper tax return deadline
If you choose to file a paper tax return, it must reach HMRC by 31 October 2026. This is three months earlier than the online deadline.
Very few people file paper returns these days — it's slower, more error-prone and gives you less time. We'd strongly recommend filing online instead, which gives you until 31 January 2027.
30 December 2026 — PAYE tax code collection deadline
This is a lesser-known but very useful deadline. If you file your online tax return by 30 December 2026 and you owe less than £3,000 in tax, you can ask HMRC to collect the tax through your PAYE tax code the following year.
This means the tax is spread across your monthly salary payments instead of paying it as a lump sum. It's only available if you:
- File online by 30 December
- Owe less than £3,000
- Already pay tax through PAYE (i.e. you have an employer)
31 January 2027 — The big deadline
This is the most important date. 31 January 2027 is the deadline for two things:
- Filing your online tax return for the 2025/26 tax year
- Paying any tax you owe for the 2025/26 tax year
If you also need to make payments on account (advance payments towards next year's tax bill), the first payment on account for 2026/27 is also due on 31 January 2027.
Important: Filing your return and paying your tax are treated as two separate obligations. Even if you file on time, you'll still be charged interest and penalties if you pay late — and vice versa.
31 July 2027 — Second payment on account
If your tax bill is over £1,000 and less than 80% of your tax was collected at source (through PAYE), you'll need to make payments on account. These are advance payments towards your next year's tax bill.
Each payment on account is half of your previous year's tax bill. The second instalment is due on 31 July 2027.
What are the penalties for missing the deadline?
HMRC's penalty system is harsh — and it starts immediately.
Late filing penalties
| How late | Penalty |
|---|---|
| 1 day late | £100 (even if you owe no tax or have a refund due) |
| 3 months late | £10 per day for up to 90 days (up to £900) |
| 6 months late | 5% of the tax due or £300 — whichever is greater |
| 12 months late | A further 5% of tax due or £300 — whichever is greater (in serious cases, up to 100% of the tax due) |
That means if you file your return 12 months late with a £5,000 tax bill, you could face penalties of £1,600 or more — on top of the tax you already owe.
Late payment penalties
| How late | Penalty |
|---|---|
| 30 days late | 5% of the tax unpaid at that date |
| 6 months late | A further 5% of tax still unpaid |
| 12 months late | A further 5% of tax still unpaid |
HMRC also charges interest on late payments. The interest rate changes periodically — as of 2025/26, it's set at the Bank of England base rate plus 2.5%. Interest is charged from the deadline date until the payment is received.
Can you get an extension?
In short — no. HMRC does not grant extensions to self-assessment deadlines. The dates are fixed and apply to everyone.
However, you may have a reasonable excuse for filing or paying late, which HMRC may accept to cancel penalties. Reasonable excuses include:
- Serious illness or bereavement of a close relative
- Your computer or software failed just before the deadline
- HMRC's online service was unavailable
- Fire, flood, or theft that prevented you from completing the return
- Unexpected postal delays
What HMRC will not accept as a reasonable excuse:
- "I didn't know I had to file a return"
- "I didn't receive a reminder from HMRC"
- "My accountant didn't file on time"
- "I couldn't be bothered"
- "I found the process too confusing"
How to file before the deadline — without the stress
The easiest way to avoid deadline stress is to file early. You can submit your 2025/26 tax return from 6 April 2026 — a full 10 months before the January deadline. Here's how to stay on top of it:
1. Gather your documents early
You'll need:
- Your P60 (from your employer, available by 31 May)
- Any P11D forms for benefits in kind
- Bank statements showing interest earned
- Invoices and receipts for self-employment income and expenses
- Rental income records if you're a landlord
- Details of any capital gains from selling assets
- Your UTR number and Government Gateway login
2. Use HMRC-recognised software
You don't need to use HMRC's own website to file your tax return. HMRC-recognised software like DTax Filer can make the process significantly easier:
- Automated tax calculation — the software calculates your tax liability as you enter your data, so you know exactly what you owe before you submit
- Step-by-step guidance — a simple wizard walks you through each section (SA100, SA105, SA106, SA109 and more)
- Direct submission to HMRC — file your return directly from the software without switching to the HMRC website
- Error checking — the software checks your return for common mistakes before submission
3. Don't wait until January
Every year, millions of people leave their tax return to the last week of January. This leads to:
- HMRC's online service slowing down or crashing under load
- Difficulty reaching HMRC helplines if you have questions
- Rushed returns with mistakes that trigger enquiries
- Stress and panic that's entirely avoidable
Filing in April, May or June means you have plenty of time, no queues, and peace of mind.
Who needs to file a self-assessment tax return?
You must file a self-assessment tax return for 2025/26 if any of the following apply:
- You were self-employed and earned more than £1,000
- You were a partner in a business partnership
- Your total income was over £150,000
- You had rental income from property
- You had foreign income that needs to be reported
- You had capital gains above the annual exempt amount
- You needed to pay the High Income Child Benefit Charge
- You received income from a trust or settlement
- You received a P800 from HMRC saying you owe tax
- HMRC has sent you a notice to file a return
If you're not sure whether you need to file, it's always better to check with HMRC or file anyway. There's no penalty for filing a return that shows zero tax due.
File your 2025/26 tax return with DTax Filer
Don't wait until the January rush. DTax Filer is HMRC-recognised software that lets you prepare, calculate and submit your self-assessment tax return in minutes — not hours.
- Prices start from just £14.50 per return
- Free trial available — no credit card required
- Supports SA100, SA105, SA106, SA107, SA109, SA110 and SA800 partnership returns
- Automated tax calculation with real-time error checking
Frequently asked questions
When is the self-assessment deadline for 2025/26?
The deadline for filing your 2025/26 self-assessment tax return online is 31 January 2027. If you're filing a paper return, the deadline is 31 October 2026. Payment of any tax owed is also due by 31 January 2027.
What happens if I miss the 31 January deadline?
You'll receive an automatic £100 penalty — even if you owe no tax. After 3 months, daily penalties of £10 begin (up to £900). After 6 months and 12 months, further penalties of 5% of tax due or £300 (whichever is greater) are added.
Can I file my 2025/26 tax return before April 2026?
No. You can only file your 2025/26 tax return from 6 April 2026 onwards, which is the day after the tax year ends. However, you can start gathering your documents and records beforehand.
Do I still need to file if I have nothing to pay?
Yes, if HMRC has sent you a notice to file a return or if you're registered for self-assessment. You must file even if your tax bill is £0. Failing to file will still result in the £100 late filing penalty.
What's the difference between filing and paying deadlines?
Filing means submitting your completed tax return to HMRC. Paying means sending the money you owe. Both have the same 31 January 2027 deadline, but they carry separate penalties. You can be penalised for filing late AND paying late — they're two independent obligations.