Self Assessment 2025/26 · Spoke · Back to pillar
Self assessment deadlines UK: filing and payment dates.
Source: gov.uk — Self Assessment deadlines.
Written by Mehmood Rajoka
Managing Partner, RR Accountants · IFA-supervised practice
Key self-assessment dates
The main deadlines are: 31 October for paper returns, 31 January for online returns and tax payment. A £100 automatic penalty applies immediately if you miss 31 January — even if you owe nothing. Payments on account (advance payments) are due 31 January and 31 July. All dates relate to the tax year ending 5 April. See gov.uk/self-assessment-tax-returns.
2025/26 self-assessment deadlines
5 April 2026
2025/26 tax year ends
Last day of the 2025/26 tax year.
5 October 2026
Register for self-assessment (new filers)
Deadline to register if you need to file for the first time for 2025/26 income.
31 October 2026
Paper self-assessment return deadline
Paper returns for 2025/26 must be filed by this date. £100 penalty if missed.
31 January 2027
Online return deadline + tax payment
Online self-assessment return must be filed. All 2025/26 tax due must be paid. First payment on account for 2026/27 also due.
31 July 2027
Second payment on account
Second advance payment towards 2026/27 tax bill (if payments on account apply).
Source: gov.uk — Self Assessment deadlines and LITRG — Self Assessment.
Penalties for late filing and payment
| Trigger | Penalty |
|---|---|
| 1 day late filing | £100 automatic penalty (even if no tax owed) |
| 3+ months late filing | £10/day for up to 90 days (£900 maximum) |
| 6+ months late filing | 5% of tax due or £300 (whichever is higher) |
| 12+ months late filing | Further 5% of tax due or £300 |
| 30 days late payment | 5% of unpaid tax |
| 6 months late payment | Additional 5% of unpaid tax |
| 12 months late payment | Another 5% of unpaid tax |
| Any late payment | Daily interest on unpaid amount from deadline |
Source: gov.uk — Self Assessment penalties.
Self-assessment deadlines — FAQs
When is the self-assessment deadline for 2025/26?
For the 2025/26 tax year (6 April 2025 – 5 April 2026): online filing deadline is 31 January 2027. Paper filing deadline is 31 October 2026. Any tax owed must be paid by 31 January 2027 — the same date as the online filing deadline.
What is the self-assessment late filing penalty?
An automatic £100 fixed penalty applies immediately if you miss the 31 January filing deadline — even if you owe no tax or have already paid. After 3 months: daily penalties of £10 per day up to 90 days (£900 maximum). After 6 months: an additional 5% of tax due or £300, whichever is higher. After 12 months: a further 5% or £300.
What are payments on account?
Payments on account are advance payments towards next year's tax bill. If your self-assessment tax bill exceeds £1,000 (and less than 80% was deducted at source), HMRC requires two advance payments — each equal to 50% of the previous year's bill. First payment: 31 January (same as filing deadline). Second payment: 31 July.
What is the deadline to register for self-assessment?
If you need to file a self-assessment return for the first time (e.g. you became a landlord, started self-employment, or received untaxed income), you must register by 5 October following the end of the tax year in which the income arose. For 2025/26 income: register by 5 October 2026.
When is self-assessment balancing payment due?
The balancing payment — the difference between your total tax liability and any payments on account already made — is due by 31 January following the end of the tax year. For 2025/26: due 31 January 2027, alongside the first payment on account for 2026/27.
What is the penalty for late payment of self-assessment tax?
5% of the unpaid tax is charged after 30 days past the payment deadline. A further 5% is charged if still unpaid after 6 months. Another 5% after 12 months. Interest also accrues on unpaid tax from the day after the deadline.
Related guides in the Self Assessment series
The pillar plus five companion spokes — and the two cross-cluster pieces this connects to.
Self Assessment — pillar guide
The full 2025/26 overview: who files, deadlines, penalties, and the MTD transition.
Do I need to file a Self Assessment?
The common triggers — side hustle, rental, dividends, £150k+ income.
How to register for Self Assessment
First-time filer? The 5 October deadline and the UTR process.
Self Assessment penalties
The £100 fixed penalty, daily penalties, and 5% surcharges explained.
Payments on account
When the 31 Jan + 31 Jul instalments apply and how to reduce them (SA303).
Self Assessment for company directors
Dividends, the £500 allowance, and when directors must file.
MTD for Income Tax
From 2026/27, qualifying landlords and sole traders move off the old annual return.
Salary vs dividend
How directors report dividend income through Self Assessment.
Don't let the 31 January deadline cost you £100 — or more.
HMRC's £100 late-filing penalty is automatic — even if you owe nothing. Late-payment surcharges and daily penalties stack on top. RR files it for you, flags the payments-on-account hit before January, and keeps you out of the penalty regime.
RR
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Chartered practice files your 2025/26 return, applies every allowance, flags payments on account, and answers HMRC enquiries. From £150+VAT. 48-hour question response.
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Estimate my tax bill first
The Self Assessment tax calculator gives you a 2025/26 estimate — useful before you decide whether to file yourself or hand it over.
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UK bookkeeping software that keeps the records HMRC expects — income, expenses, dividends — so filing in January isn't a scramble.
See SmartBooksAbout the author
Mehmood Rajoka, Managing Partner, RR Accountants
Managing Partner at RR Accountants — a UK practice supervised by the Institute of Financial Accountants. Specialist focus on UK landlord and property tax, MTD for Income Tax, and limited-company advisory. RR Accountants serves clients across nine physical UK offices plus Glasgow service area.
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This guide is general information about UK tax rules. It is not personal tax advice. For advice tailored to your situation, speak to a regulated UK accountant. All figures and dates verified against gov.uk as of . Self Assessment deadlines and penalty rules can change — re-check primary sources before acting.