Self Assessment deadline: 31 January 2027
Dates and penalties from GOV.UK: Self Assessment deadlines, Payments on account and Penalties.
The deadline to file your 2025/26 Self Assessment tax return online, and pay the tax you owe, is midnight on Sunday 31 January 2027. The return covers the tax year from 6 April 2025 to 5 April 2026. The date is the easy part. What catches people out is the amount, because in January you often pay part of next year's tax too. Use the calculator below to see exactly what you'll owe, then read on for the other dates, the penalties, and what to do if you can't pay.
What will I pay on 31 January?
From your tax return calculation: Income Tax, Class 4 NI, student loan and any Capital Gains Tax.
These are left out when HMRC works out payments on account.
The amounts you paid in January 2026 and July 2026. Enter £0 if this is your first year.
A guide only. Your HMRC online account shows the exact amounts due.
All the Self Assessment dates for 2025/26
| Date | What's due |
|---|---|
| 5 October 2026 | Register for Self Assessment, if 2025/26 was your first year (passed) |
| 31 October 2026 | Paper tax return deadline (passed) |
| 30 December 2026 | File online by this date if you owe less than £3,000 and want it collected through your PAYE tax code instead |
| 31 January 2027 | File the online return, pay the balance of tax for 2025/26, and pay the first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
31 January 2027 is a Sunday. You can still file online and pay by Faster Payments (online or telephone banking) over the weekend. But if you pay by Bacs, CHAPS or cheque, the money must reach HMRC by the last working day before, which is Friday 29 January. A Direct Debit needs setting up at least 3 working days beforehand.
If you missed the 5 October deadline to register, register now. You still have to file and pay by 31 January, and you may be charged a penalty if you then pay late. HMRC needs time to send your Unique Taxpayer Reference (UTR) by post, so don't leave it until January.
Why January can cost far more than you expect
If your tax bill is over £1,000, and less than 80% of your tax is already taken at source, HMRC asks for payments on account: two advance payments towards next year's bill, each worth half of this year's. They're due on 31 January and 31 July.
First year, £5,000 bill: you haven't made any payments on account yet. On 31 January you pay the £5,000 for 2025/26 plus a £2,500 payment on account for 2026/27, so £7,500. Another £2,500 is due on 31 July.
Second year, £6,000 bill, £5,000 already paid on account: on 31 January you pay the £1,000 balance plus a £3,000 payment on account for 2026/27, so £4,000. Another £3,000 is due on 31 July.
If you expect your income to fall in 2026/27, you can ask HMRC to reduce your payments on account, online or with form SA303. Reduce them only if you're confident: if they turn out too low, you'll pay interest on the difference. Our guide to how self-employment tax works explains payments on account in more detail.
Estimate the bill itself
Self-Employed Tax Calculator (UK)
Enter your income and expenses to see your Income Tax, Class 4 NI and student loan repayments, then use the figure above to see what's due in January.
Open the calculator →Penalties for missing 31 January
Filing late:
- 1 day late: an automatic £100 penalty, even if you owe no tax or pay on time.
- 3 months late: £10 a day, for up to 90 days (£900).
- 6 months late: a further 5% of the tax due, or £300 if that's more.
- 12 months late: another 5% of the tax due, or £300 if that's more. It can be higher if HMRC thinks you deliberately withheld information.
Paying late: interest is charged from 1 February at the Bank of England base rate plus 4%. Late payment penalties of 5% of the unpaid tax are added at 30 days, 6 months and 12 months.
You can appeal a penalty if you had a reasonable excuse, such as a serious illness or a bereavement close to the deadline. Forgetting, or finding the return complicated, doesn't count.
What if you can't pay in full?
File on time anyway. Filing and paying are separate. Filing on time avoids the £100 penalty and the daily penalties, even if you can't pay yet.
Then set up a Time to Pay arrangement. If you owe £30,000 or less, have filed your return, and set it up within 60 days of the deadline, you can usually arrange monthly instalments online without speaking to anyone. Interest still applies, but a payment plan that you stick to avoids the late payment penalties. If you owe more, or need longer, call HMRC's Self Assessment payment helpline.
Before you file: a quick checklist
- Your UTR (10 digits) and Government Gateway sign-in details. Allow time if you need a new activation code by post.
- Your total income and allowable expenses for 6 April 2025 to 5 April 2026, from your records or bank statements.
- P60 or P45 if you also had a job, and P11D details for any benefits.
- Rental income and costs, if you're a landlord. Remember mortgage interest goes in as a tax credit, not an expense. See buy-to-let costs.
- Pension contributions and Gift Aid donations, which can reduce the tax for higher-rate taxpayers.
- Dividends, savings interest and any gains from selling shares, crypto or a second property.
For the 2025/26 year, the Income Tax bands and Class 4 NI rates were the same as they are now. See sole trader tax rates and thresholds. One difference: dividends were taxed at 8.75% and 33.75% in 2025/26, before the April 2026 rise.
Do you need to file at all?
You usually need to file if, in 2025/26, you:
- were self-employed with income over £1,000 (the trading allowance)
- had rental income over £1,000 (the property allowance)
- were a partner in a business partnership
- had untaxed income, such as large savings interest or foreign income, that isn't taxed through PAYE
- had Capital Gains Tax to pay that you didn't report through the 60-day property service
- had to pay the High Income Child Benefit Charge, unless you've chosen to pay it through your tax code
If you're not sure, HMRC has a free online tool, "Check if you need to send a Self Assessment tax return", on GOV.UK. If you no longer need to file, tell HMRC, or you may still get a penalty for a return they're expecting.
Common mistakes
Budgeting for the bill but not the payment on account. In your first year, January can be one and a half times your tax bill. Use the calculator above early.
Leaving it to the last week. HMRC's systems and helplines are at their busiest in late January, and sign-in problems take days to fix.
Using last year's payment reference. Your Self Assessment payment reference is your 10-digit UTR followed by the letter K. Check it on your statement or online account.
Not filing because you can't pay. The penalties for filing late are separate from, and on top of, those for paying late.
Related guides and calculators
- Sole trader tax rates and thresholds: the bands, NI and combined rates.
- How self-employment tax works: expenses, payments on account and a worked example.
- Corporation Tax deadlines: the different dates if you run a limited company.
- Self-employed tax calculator.
Frequently asked questions
When is the Self Assessment deadline for 2025/26?
The deadline to file your 2025/26 Self Assessment tax return online is 31 January 2027. That's also the deadline to pay any tax you owe for 2025/26 and your first payment on account for 2026/27. The paper return deadline was 31 October 2026.
What happens if I miss the 31 January deadline?
You get an automatic £100 penalty for filing late, even if you owe no tax. After 3 months, £10 a day is added for up to 90 days, then more at 6 and 12 months. If you pay late, interest is charged from 1 February, with penalties of 5% of the unpaid tax at 30 days, 6 months and 12 months.
Why is my January tax bill so high?
Usually because of payments on account. If your bill is over £1,000, HMRC asks for half of next year's tax in advance on 31 January, on top of what you owe for the year just finished. In your first year that can make January one and a half times your tax bill.
Can I pay my Self Assessment tax in instalments?
Yes. If you owe £30,000 or less and have filed your return, you can usually set up a Time to Pay arrangement online within 60 days of the deadline and pay monthly. Interest still applies. You can also make voluntary payments in advance through a budget payment plan.
What is the payment reference for Self Assessment?
Your 10-digit Unique Taxpayer Reference (UTR) followed by the letter K, for example 1234567890K. You'll find it on your HMRC statements and in your online account.
When is the second payment on account due?
On 31 July 2027 for the 2026/27 tax year. It's normally the same as the first payment on account, which is half of your 2025/26 tax bill, excluding student loan repayments and Capital Gains Tax.