What is the Self Assessment tax return deadline?
The Self Assessment online filing deadline is 31 January following the end of the tax year. For 2024/25 the online deadline is 31 January 2026 and the paper deadline is 31 October 2025.
Detailed Explanation
Self Assessment covers the UK tax year, which runs from 6 April to 5 April the following year. For the 2024/25 tax year (6 April 2024 to 5 April 2025) there are two filing deadlines depending on how you submit.
Paper returns must reach HMRC by 31 October 2025. Online returns must be submitted by 31 January 2026. Any tax owed for 2024/25 must also be paid by 31 January 2026, regardless of whether you file on paper or online.
If you have a payment on account obligation, a second payment on account for 2024/25 is due by 31 July 2025. Payments on account are advance payments towards your next year's tax bill. They are required when your Self Assessment tax liability exceeds £1,000 and less than 80% of your tax is collected at source. Each payment is 50% of the previous year's liability.
Penalties for missing the online deadline escalate automatically. One day late triggers an immediate £100 fixed penalty, even if no tax is owed and even if the tax has already been paid. After three months late (1 May 2026 for 2024/25 online returns), HMRC adds £10 per day for up to 90 days, which is a further £900 maximum. After six months late (1 August 2026), a further penalty of the higher of £300 or 5% of the tax due is charged. After twelve months late (1 February 2027), another penalty at the same level is added. In cases of deliberate withholding, HMRC can charge up to 100% of the tax due.
For late payment, HMRC charges interest at their official rate plus 2.5 percentage points. In 2025/26 this is approximately 7.25% per annum on the overdue amount. There are also 5% surcharges on unpaid tax at 30 days, 6 months, and 12 months after the payment deadline.
You must register for Self Assessment before you can file. The registration deadline for the 2024/25 tax year is 5 October 2025. You must register if you are self-employed with income over £1,000, a company director, a higher or additional rate taxpayer, have untaxed income such as rent or investment returns, or earn over £100,000 in the year.
If you receive a notice to file from HMRC, you must submit a return even if you have no tax to pay. Ignoring the notice does not remove the obligation and the £100 penalty will apply.
If you have a reasonable excuse for filing late, such as a serious illness, bereavement of a close relative, or a genuine system failure outside your control, you can appeal penalties through HMRC's online service. Not having your paperwork ready, forgetting the deadline, or being too busy are not accepted as reasonable excuses.
For the 2024/25 tax year the key dates in full are: 5 October 2025 to register for Self Assessment; 31 October 2025 for paper returns; 31 January 2026 for online returns and all tax payments; 31 July 2026 for the first payment on account for 2025/26.
AccountsOS tracks your Self Assessment deadline automatically and sends reminders well in advance. Finn can help you pull together salary, dividend, and expense figures so you have everything ready before January.
Source: https://www.gov.uk/self-assessment-tax-returns/deadlines
Real-World Examples
Company director with salary and dividends
A limited company director paying themselves a small salary and dividends must file a Self Assessment return. The online deadline for their 2024/25 return is 31 January 2026. Filing one day late triggers an automatic £100 penalty even if all tax has already been paid.
Freelancer who forgot to register
A freelancer who started trading in October 2024 and missed the 5 October 2025 registration deadline should register immediately and file as soon as possible. The accumulated daily penalties grow quickly, so acting fast reduces the total fine.
Paper filer switching to online
A sole trader who has always filed on paper by 31 October wants to switch to online this year to gain the extra three months until 31 January 2026. They should confirm the switch before the October paper deadline passes to avoid a late paper filing penalty.
Common Mistakes to Avoid
- Assuming 31 January is only the payment deadline, not realising it is also the online filing deadline.
- Filing a paper return after 31 October and expecting the online deadline of 31 January to still apply.
- Not registering for Self Assessment by 5 October, which must happen before you can file at all.
- Ignoring the £100 automatic penalty because no tax is owed, not realising the penalty still stands regardless of the tax position.
Frequently Asked Questions
What happens if I miss the Self Assessment deadline?
An automatic £100 penalty applies from day one. After 3 months, £10 per day for up to 90 days. Further 5% surcharges on unpaid tax apply at 6 and 12 months.
Can I get an extension on the Self Assessment deadline?
HMRC does not grant routine extensions. You can appeal penalties after filing if you had a genuine reasonable excuse such as serious illness or bereavement.
Is the deadline different for paper returns?
Yes. Paper returns must be filed by 31 October. Online returns have a later deadline of 31 January following the end of the tax year.
When must I pay the tax owed on my Self Assessment?
All tax owed for the previous tax year is due by 31 January, the same date as the online filing deadline. Interest accrues from the day after on any unpaid amount.
What is a payment on account?
Advance payments towards the next year's tax bill, each equal to 50% of the previous year's liability. Due on 31 January and 31 July each year.
Do I need to file if I have no tax to pay?
If HMRC has issued a notice to file, you must submit a return even with no tax due. The £100 late filing penalty applies regardless of the tax position.
Practical Tips
- Set a calendar reminder for 31 January each year, plus a second reminder in early December to give yourself six weeks to gather documents.
- Register for Self Assessment by 5 October following the end of the tax year in which you first needed to file.
- File early even with estimated figures and amend later. Early filing stops the clock on late filing penalties immediately.
- Use AccountsOS throughout the year so your income and expense figures are already compiled well before January.
Related Questions
Can I complete my own Self Assessment tax return?
Yes, you can complete your own Self Assessment tax return using HMRC's free online service. Most straightforward returns for directors with salary and dividends take two to four hours. Complex situations with overseas income, capital gains, or income above £100,000 may benefit from professional help.
What expenses can I claim on Self Assessment?
On Self Assessment you can claim allowable business expenses that are incurred wholly and exclusively for the purpose of your trade. Common categories include office costs, travel, professional fees, equipment, and a proportion of home costs where you work from home.
Do company directors need to file Self Assessment?
Usually yes. Most directors need to file Self Assessment if they receive dividends, salary above £100,000, or have other income. HMRC typically writes to new directors to register.
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