Self Assessment can feel like a lot of dates and rules rolled into one. This article walks through the deadlines for the 2025/26 tax return in plain English, so you know what has already passed, what is still to come and what to do next. It is general information, not personal advice, and your own circumstances may differ.
What it means
Self Assessment is the system HMRC uses to collect Income Tax on income that has not already been taxed, such as self-employment profits and rental income. You report your income and gains for a tax year on a Self Assessment return, and HMRC works out what you owe.
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. The return for that year is the one now due.
Who it affects
You may need to file a 2025/26 return if you are, for example:
- a sole trader or self-employed person
- a landlord receiving rental income
- a company director with income that has not been taxed at source
- someone with other untaxed income
The exact rules on who must file are on GOV.UK, and it is worth checking them if you are unsure. If you have never filed before, you needed to register for Self Assessment by 5 October 2026.
Current rules and requirements
Filing deadlines
The deadline for paper returns for 2025/26 was midnight on 31 October 2026. That date has now passed. The deadline for online returns is midnight on 31 January 2027, so there is still time to file online.
Paying what you owe
Any tax owed for 2025/26 (the balancing payment) must be paid by 31 January 2027. Filing early does not mean paying early. Tax is still due by 31 January 2027 whenever you file.
Payments on account
Payments on account are advance payments towards the next year's tax bill. Each is usually half of the previous year's bill. The first payment on account for 2026/27 is due by 31 January 2027 and the second by 31 July 2027.
You do not need to make them if your last Self Assessment bill was under £1,000, or if more than 80% of the tax owed was already deducted at source, for example through PAYE.
Collecting tax through your tax code
If you are employed or receive a UK pension, owe less than £3,000 and file online by 30 December 2026, you may be able to have your 2025/26 tax collected through your PAYE tax code instead of paying in a lump sum.
Penalties and interest
Filing up to 3 months late incurs an automatic £100 penalty, even if no tax is owed. Further penalties apply if the return is later still, and interest is charged on tax paid late.
If you cannot pay in full
You may be able to set up a payment plan (Time to Pay) with HMRC. It is best to contact HMRC as early as possible rather than waiting until after the deadline.
Important dates, thresholds and figures
| Item | Date or figure |
|---|---|
| 2025/26 tax year | 6 April 2025 to 5 April 2026 |
| Register for Self Assessment (new filers) | 5 October 2026 (passed) |
| Paper return deadline | 31 October 2026 (passed) |
| Online filing for tax code collection | 30 December 2026 |
| Online return deadline | 31 January 2027 |
| Balancing payment for 2025/26 | 31 January 2027 |
| First payment on account for 2026/27 | 31 January 2027 |
| Second payment on account for 2026/27 | 31 July 2027 |
| Payments on account not needed if | Last bill under £1,000, or over 80% taxed at source |
| Tax code collection limit | Under £3,000 owed |
| Late filing penalty (up to 3 months) | £100 |
Worked example
This is a simplified illustration with made-up figures.
Sam is a sole trader who files online on 15 January 2027. Their 2025/26 tax bill is £4,000, and their 2024/25 bill was also above £1,000 with less than 80% taxed at source.
By 31 January 2027, Sam needs to pay:
- the £4,000 balancing payment for 2025/26
- a first payment on account for 2026/27, usually half of the 2025/26 bill, so £2,000
That is £6,000 in total on 31 January. The second payment on account of £2,000 follows by 31 July 2027. Filing on 15 January did not move the payment date. Sam can plan ahead by setting money aside each month.
Common mistakes
- Assuming the deadline has passed. The paper deadline has gone, but the online deadline of 31 January 2027 is still ahead.
- Thinking early filing means early payment. The payment date stays the same.
- Forgetting payments on account. The 31 January bill can be much larger than expected because it may include the first advance payment.
- Assuming no tax means no penalty. A late return can still trigger the £100 penalty.
- Leaving it to the last week. Gathering records, and getting help if you need it, takes time.
- Missing the 30 December date if you want tax collected through your tax code.
Frequently asked questions
Can I still file my 2025/26 return?
Yes. The paper deadline has passed, but you can file online until midnight on 31 January 2027.
Do I have to pay on the day I file?
No. Payment is due by 31 January 2027, whether you file in November or on the deadline itself.
What if I cannot pay in full?
You may be able to set up a Time to Pay arrangement with HMRC. Contact them as soon as possible.
Will I be fined if I owe nothing?
Potentially, yes. A return filed late can incur the automatic £100 penalty even if no tax is owed.
Practical next steps
- Check whether you need to file a 2025/26 return.
- Gather your income and expense records for 6 April 2025 to 5 April 2026.
- Confirm whether you could use the tax code option, and if so aim to file online by 30 December 2026.
- Work out your likely bill, including any payments on account, and start setting money aside.
- File online well before 31 January 2027.
How 360 Accounts can help
If you would like a second pair of eyes, we can help with preparing and filing your return, estimating what you will owe and planning for the January payment. We work with sole traders, landlords, directors and small businesses in Guildford, Woking and across the UK.
Official references
- GOV.UK: Self Assessment tax returns (https://www.gov.uk/self-assessment-tax-returns)
- GOV.UK: Self Assessment tax returns deadlines (https://www.gov.uk/self-assessment-tax-returns/deadlines)
- GOV.UK: Understand your Self Assessment penalties (https://www.gov.uk/self-assessment-tax-returns/penalties)
- GOV.UK: Pay your Self Assessment tax bill (https://www.gov.uk/pay-self-assessment-tax-bill)