The Self Assessment deadline for the 2025/26 tax year is midnight on 31 January 2027. By then you must file your online tax return and pay what you owe for 2025/26. You may also have to make your first payment on account towards 2026/27 on the same day. The paper return deadline (31 October 2026) has passed, so filing online is now the only option. A late return means an automatic £100 penalty, even if you owe no tax.
If you pay through PAYE and owe less than £3,000, filing online by 30 December 2026 lets HMRC collect the tax through your tax code instead of in one payment. This guide sets out what to do now, week by week, so you are not rushing on 31 January.
Self Assessment Deadline Dates for 2025/26
| Date | What it is for |
|---|---|
| 5 October 2026 | Deadline to register for Self Assessment if you are new (passed: register now if you missed it) |
| 31 October 2026 | Paper tax return deadline (passed) |
| 30 December 2026 | File online by this date if you want a bill under £3,000 collected through your PAYE tax code |
| 31 January 2027 | Online return deadline, balancing payment for 2025/26 and first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
HMRC’s own guide to Self Assessment tax returns sets out who must file and the full list of deadlines.
What to Do Now: A Week-by-Week Plan
November: check you are registered and can log in
If this is your first return and you have not registered, do it now. Your Unique Taxpayer Reference (UTR) arrives by post and can take a couple of weeks. Then check you can sign in to your HMRC online account, because setting up access can also take time. Our guide to filing your first Self Assessment walks through the set-up.
Early December: gather your records
- P60 and any P45s or P11D forms from employment
- Self-employed income and expenses for the year to 5 April 2026
- Rental income and costs, if you are a landlord
- Bank and savings interest, dividends and pension statements
- Details of any assets you sold, for Capital Gains Tax
- Gift Aid donations and personal pension contributions you paid
By 30 December: file if you want to pay through your tax code
If you are employed or receive a pension, owe less than £3,000 and want the tax collected through your PAYE tax code over the next tax year, file online by 30 December 2026. HMRC explains the conditions in its guide to paying your Self Assessment bill.
January: file, check and pay
File as early in January as you can. HMRC then shows you the exact amount due, including any payment on account. Pay by 31 January. If you pay by bank transfer, allow time for the payment to reach HMRC.
Payments on Account: The First-Year Surprise
If your 2025/26 bill is more than £1,000, and less than 80% of your tax was collected at source, HMRC will usually ask for payments on account towards next year. Each one is half of this year’s bill. The first is due on 31 January, alongside your balancing payment. This is why many people meeting the Self Assessment deadline for the first time owe much more than they expected.
Worked Example: A New Sole Trader’s January Bill
Sam started self-employment in 2025/26 and this is their first return. Their Income Tax and Class 4 National Insurance for 2025/26 comes to £6,000. The figures are illustrative.
| Payment | Due date | Amount |
|---|---|---|
| Balancing payment for 2025/26 | 31 January 2027 | £6,000 |
| First payment on account for 2026/27 (50%) | 31 January 2027 | £3,000 |
| Total due on the Self Assessment deadline | 31 January 2027 | £9,000 |
| Second payment on account for 2026/27 | 31 July 2027 | £3,000 |
If Sam expects lower profits in 2026/27, they can ask HMRC to reduce the payments on account, but they will pay interest if the reduction turns out to be too large.
What Happens If You Miss the Self Assessment Deadline?
| When | Late filing penalty | Late payment penalty |
|---|---|---|
| 1 day late | £100 | Interest starts |
| 30 days late | No change | 5% of the tax unpaid |
| 3 months late | £10 a day, up to £900 | Interest continues |
| 6 months late | 5% of the tax due or £300, whichever is greater | A further 5% |
| 12 months late | Another 5% or £300, whichever is greater | A further 5% |
Interest is charged on late tax every day. HMRC’s late payment interest rate is 8% a year from 24 November 2026, set at the Bank of England base rate plus 4%. See HMRC’s page on interest rates for late payments. If you have already missed a deadline, read our rescue plan for late Self Assessment and our guide to avoiding late filing penalties.
If You Cannot Pay by 31 January
File your return on time anyway. That stops the late filing penalties, and you cannot set up a payment plan until the return is filed. If you owe £30,000 or less, you may be able to set up a Time to Pay arrangement online without calling HMRC. For larger amounts, or if you need longer, you can still apply but must contact HMRC. HMRC explains the options in if you cannot pay your tax bill on time. Our guide on avoiding penalties for late payments has more tips.
Common Mistakes Before the Self Assessment Deadline
- Leaving it to the last week: HMRC’s systems and phone lines are busiest in late January, and login problems can take days to fix.
- Forgetting other income: bank interest above your savings allowance, dividends, rental income and gains all need to be reported.
- Missing allowable expenses: sole traders and landlords often under-claim costs they are entitled to deduct.
- Not claiming reliefs: higher-rate taxpayers can claim extra relief on Gift Aid and personal pension contributions through the return.
- Ignoring the payment on account: budget for it, or ask HMRC to reduce it if your income has fallen.
- Using the wrong payment reference: your reference is your 10-digit UTR followed by the letter K.
Our guide to deductions people miss in their Self Assessment covers the most common ones.
Making Tax Digital Does Not Change This Deadline
Making Tax Digital for Income Tax started on 6 April 2026 for sole traders and landlords with qualifying income over £50,000. It covers the 2026/27 tax year onwards. Your 2025/26 return is still filed in the usual way by the 31 January 2027 Self Assessment deadline.
Frequently Asked Questions
When is the Self Assessment deadline for 2025/26?
Midnight on 31 January 2027 for online returns and for paying any tax owed. The paper deadline was 31 October 2026.
Can I still file a paper return?
You can, but because the 31 October 2026 paper deadline has passed, it will be late and you will get a penalty. File online instead.
Do I get a penalty if I file late but owe no tax?
Yes. The £100 late filing penalty applies even if you owe nothing. You can appeal if you had a reasonable excuse.
What is a payment on account?
An advance payment towards next year’s tax, usually half of this year’s bill, due on 31 January and 31 July. It applies if your bill is over £1,000.
What if I cannot pay my Self Assessment bill on time?
File on time, then set up a payment plan. If you owe £30,000 or less, you may be able to do this online. Interest still applies.
Can someone else file my tax return for me?
Yes. An accountant can file it as your agent once you have authorised them. See our Self Assessment service.
Conclusion
The Self Assessment deadline for 2025/26 is 31 January 2027, but the work starts now. Check you are registered, gather your records in December, file early in January and plan for any payment on account. If you cannot pay in full, file on time and set up a payment plan.
If you would rather hand it over, our tax return service prepares and files your return for a fixed fee agreed upfront. Call 01204 859315, email [email protected] or book a call.
