For the UK 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026, the key Self Assessment deadlines are 5 October 2026 to register for first-time filers, 31 October 2026 for paper tax returns, and 31 January 2027 for online returns and payment of any tax due. Missing these deadlines can result in significant penalties, starting automatically with a 100 pounds charge.
Who must file a Self Assessment tax return for 2025/26?
Self Assessment is HMRC's system for collecting income tax from individuals whose earnings are not fully taxed through the Pay As You Earn (PAYE) system. This includes a range of taxpayer categories to ensure all income is declared and correctly taxed. The system captures income sources that are not automatically deducted at source.
You are typically required to file a Self Assessment tax return if you fall into one of several categories. This includes self-employed individuals earning more than 1,000 pounds, which is the current trading allowance threshold. Partners in a partnership must also file, as do company directors who receive untaxed income. High earners, specifically individuals earning more than 150,000 pounds in the tax year, are mandated to submit a return. Landlords whose rental income exceeds the property allowance are also within the Self Assessment system. Individuals with capital gains above the annual exempt amount must declare these. Recipients of the High Income Child Benefit Charge are required to file. Additionally, those with untaxed savings income, dividend income, or foreign income above specific HMRC thresholds must use Self Assessment to declare these earnings.
When are the key Self Assessment deadlines for 2025/26 income?
The 2025/26 UK tax year ended on 5 April 2026. The deadlines below apply to income earned in that period.
- 5 October 2026: First-time filers must register with HMRC by this date. Registration triggers issue of your Unique Taxpayer Reference (UTR), which you need to file.
- 31 October 2026: Paper return deadline for 2025/26.
- 31 January 2027: Online return deadline for 2025/26, plus payment of any balancing tax due AND the first payment on account for 2026/27 if applicable.
- 31 July 2027: Second payment on account for 2026/27.
How do I register for Self Assessment?
New taxpayers must register for Self Assessment online via the gov.uk website. After successful registration, HMRC will send a Unique Taxpayer Reference (UTR) by post, typically within approximately 10 working days. This UTR is a ten-digit number essential for accessing your online tax account and submitting your return. Filing cannot proceed without this unique identifier.
What are Self Assessment payments on account?
Payments on account are advance instalments towards your next year's tax bill. They are designed to help spread the cost of tax for those with significant untaxed income. Each payment on account is typically equal to half of your previous year's Self Assessment tax liability.
These payments are due twice a year: the first by 31 January and the second by 31 July. For the 2025/26 tax year, if you made a balancing payment on 31 January 2027, you would also likely pay the first instalment for the 2026/27 tax year. The second instalment for 2026/27 would then be due by 31 July 2027.
Payments on account are not always required. You will not need to make them if your previous year's Self Assessment tax bill was less than 1,000 pounds, or if more than 80 per cent of your tax was collected at source, for example, through PAYE deductions from an employment salary. This ensures that only those with a significant tax liability outside of PAYE need to make these advance payments.
What are the penalties for late Self Assessment filing or payment?
HMRC's late-filing and late-payment penalties accumulate fast and can substantially exceed any tax owed.
How do late-filing penalties escalate?
The schedule is staged:
- Initial 100 pounds: A penalty of 100 pounds is charged automatically the day after the online filing deadline of 31 January, regardless of whether any tax is owed.
- Daily charges: If the return remains unfiled for three months, a further penalty of 10 pounds per day is charged. This daily charge can accumulate for up to 90 days, leading to a maximum additional penalty of 900 pounds.
- Six-month penalty: At six months late, an additional penalty is applied. This is the greater of 300 pounds or 5 per cent of the tax due.
- Twelve-month penalty: If the return is still not filed at 12 months late, another penalty applies. This is again the greater of 300 pounds or 5 per cent of the tax due.
A return filed 12 months late therefore incurs at least 1,600 pounds in penalties before any tax or interest.
How does late-payment interest apply?
Late-payment interest is charged on any unpaid Self Assessment tax from the day after the payment deadline. For the 2025/26 tax year, this interest would begin to accrue from 1 February 2027. HMRC sets this late-payment interest rate as the Bank of England Bank Rate plus 4 percentage points. This interest applies to both the balancing payment and any payments on account that are not settled by their due dates.
Can I appeal a penalty?
HMRC's 'reasonable excuse' procedure lets you appeal a late-filing penalty when a serious circumstance prevented timely filing. Recognised excuses include bereavement of a close relative, serious illness, computer or software failure around the deadline, postal delay, or a disability that impacts filing. Each appeal is assessed individually.
Will Making Tax Digital for Income Tax change Self Assessment from 2026?
Making Tax Digital for Income Tax Self Assessment (MTD ITSA) is a separate digital quarterly regime in how certain taxpayers will report their income to HMRC. While separate from the core Self Assessment regime, it directly impacts many individuals who currently file Self Assessment returns.
MTD ITSA phases in from 6 April 2026 for self-employed individuals and landlords with qualifying income above 50,000 pounds. These taxpayers will be required to submit quarterly digital updates of their income and expenses through MTD-compatible software. This is in addition to the annual Self Assessment tax return. The regime expands further: from 6 April 2027, MTD ITSA will extend to those with qualifying income above 30,000 pounds. From 6 April 2028, it will include those with qualifying income above 20,000 pounds, as confirmed in the Autumn Statement 2024. These changes mean affected taxpayers will need to maintain digital records and file more frequently than the annual Self Assessment return. For those below these thresholds, the standard Self Assessment process continues unchanged for now.
What should you do next?
For the 2025/26 tax year, ensure you are registered for Self Assessment by 5 October 2026 if you have not filed before. File your return, ideally online, by the 31 January 2027 deadline. Pay any tax due, including your first payment on account for 2026/27, by this date. Mark 31 July 2027 for your second payment on account for 2026/27. If you anticipate difficulty paying your tax bill by 31 January, HMRC offers a Time to Pay arrangement. This allows you to spread payments over up to 12 months, and can be set up online at gov.uk if your bill is under 30,000 pounds and your return has been filed. Proactive management of your tax obligations is key to avoiding penalties and interest.