Self Assessment Deadline 31 January 2027: Why You Should Start Your Return This Week
Gary Winterborne - AATQB, AATQB
Self Assessment Deadline 31 January 2027: Why You Should Start Your Return This Week
Thirty-first of January sounds miles away, but it really isn't. Between the run-up to Christmas, New Year and getting back into work, January tends to disappear. If you need to file a Self Assessment tax return for 2025/26, here's what's due, who it affects and how to get it done calmly rather than in a last-minute rush.
Key Takeaways
- As of 9th November 2026, the online deadline for 2025/26 Self Assessment returns is 31 January 2027.
- Any tax you owe for 2025/26 must be paid by the same date, and a first payment on account for 2026/27 may also be due.
- File even one day late and there's an automatic £100 penalty, even if you have no tax to pay.
- The paper return deadline of 31 October 2026 has passed, so online filing is now the route.
- Pulling your records together now means you'll know your bill well before it's due.
Why 31 January sneaks up on everyone
Every year, plenty of capable, organised business owners find themselves scrambling in the last week of January. It's not because they don't care. It's because the deadline lands at the busiest, most distracted time of year.
By the time the decorations come down, you may have only a few working weeks left. If you're also chasing invoices, dealing with quieter trading or catching up after a break, the tax return gets pushed to the back of the queue. That's exactly when mistakes happen.
Who needs to file a Self Assessment return?
This return covers the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026. You'll generally need to file if you were self-employed and your trading income was above the £1,000 trading allowance for that year.
Sole traders aren't the only ones. If you had other income that hasn't already had tax taken off, such as some rental income, you may need to file too. If you're not sure, it's worth checking rather than guessing.
If this is your first time, you needed to register for Self Assessment by 5 October 2026. If you've missed that, don't ignore it. Register as soon as you can and get some advice on next steps.
What's due on 31 January 2027
Two things happen on the same day, and people often only think about the first one. You need to file your return online and pay any tax you owe.
Deadlines to put in your diary
As of 9th November 2026: your 2025/26 return must be filed online by 31 January 2027. Any tax owed for 2025/26 (the balancing payment) is also due by 31 January 2027. Where payments on account apply, your first payment towards 2026/27 is due that day too, with the second due by 31 July 2027. The paper deadline of 31 October 2026 has already passed.
Payments on account are the bit that catches people out. In simple terms, they're advance payments towards next year's tax bill. Not everyone has to make them, but if you do, your January payment could be noticeably bigger than you expected. Knowing your figures early gives you time to plan for it.
What happens if you miss the deadline?
HMRC doesn't wait. If your return is filed even one day late, there's an automatic £100 penalty. That applies even if you owe no tax at all, which surprises a lot of people.
It doesn't stop there. Further late filing penalties kick in if your return is still outstanding after three months, six months and twelve months. Late payment penalties are separate, and interest is charged on tax paid late. As of 9th November 2026, that interest rate is linked to the Bank of England base rate, so it changes over time.
The short version: filing late and paying late are two separate problems, and both cost money.
The mistake we see every year
Here's the pattern. Someone leaves their return until mid-January, sits down to do it, and realises receipts are missing, bank statements haven't been downloaded and there's a mileage log that doesn't exist. Panic follows.
The fix is simple: get your records together now, while there's time to find what's missing.
Your records checklist for 2025/26
- Business bank statements from 6 April 2025 to 5 April 2026
- Sales invoices and records of all income received
- Receipts for business expenses
- Mileage or vehicle records if you use a vehicle for work
- Details of any other untaxed income, such as rental income
- Your Unique Taxpayer Reference (UTR) and HMRC online login details
Once that's together, the return itself becomes far less daunting. And you'll know what you owe before the bill lands, rather than finding out the week it's due.
How to get started this week
You don't need to finish everything in one sitting. Just start. Gather your paperwork, check you can log in to your HMRC account, and make a rough note of your income and expenses.
If you'd rather hand it over, our personal tax returns service takes care of the return from start to finish. If you're self-employed and want your figures kept in order all year, have a look at our sole trader accounts support. From our offices in Guildford and Woking we help clients right across the UK, and the earlier you get in touch, the smoother it goes.
Your Questions Answered
When is the Self Assessment deadline for 2025/26?
As of 9th November 2026, online returns for the 2025/26 tax year must be filed by 31 January 2027.
Can I still send a paper return?
The paper deadline for 2025/26 was 31 October 2026, so that has now passed and online filing is the remaining route.
Will I be fined if I file late but owe no tax?
Yes. There's an automatic £100 penalty for filing late, even if you have nothing to pay.
When do I have to pay the tax I owe?
Any tax owed for 2025/26 is due by 31 January 2027, the same day as the filing deadline, and a first payment on account for 2026/27 may also be due then.
Do I need to file if I only earned a little from self-employment?
Generally, if your self-employed income was above the £1,000 trading allowance, you'll need to file, and other untaxed income may mean you need to file anyway.
I missed the 5 October registration deadline. What now?
Register for Self Assessment as soon as possible and speak to an accountant about getting your return filed on time.
Not sure where you stand?
Our Guildford team can check whether you need to file, what you're likely to owe and get your return in well before 31 January. Get in touch with 360Accounts.
WEBSITE Q&A SNIPPET — DROP INTO ANY PAGE
When is the online Self Assessment deadline for 2025/26?
As of 9th November 2026, online Self Assessment returns for the 2025/26 tax year must be filed by 31 January 2027.
When must I pay my 2025/26 Self Assessment tax?
Any tax owed for 2025/26 must be paid by 31 January 2027, and a first payment on account for 2026/27 may be due the same day.
Is there a penalty for filing late if I owe no tax?
Yes, filing a Self Assessment return even one day late triggers an automatic £100 penalty, even if there is no tax to pay.
Do sole traders always need to file a Self Assessment return?
Sole traders whose self-employment income is above the £1,000 trading allowance in a tax year generally need to file a Self Assessment return.
Gary Winterborne - AATQB
Meet Gary! From professional cricketer to business owner, Gary has enjoyed a varied career, running businesses across industries including construction and retail. His hands-on experience means he understands the challenges business owners face. Friendly, approachable and passionate about helping others succeed, Gary brings real-world business knowledge to 360 Accounts & Bookkeeping. He believes accounting should be straightforward, stress-free and focused on helping your business grow.