Notes
Self assessment deadline and penalties in the UK
The online filing deadline for your self assessment return is 31 January of the year after the tax year ends. Miss it and you face a £100 fixed penalty immediately, then £10 per day after three months, then 5% of the tax owed at six months and again at 12 months. You can appeal if you have a reasonable excuse, such as serious illness or bereavement.
If you are filing for the first time, register with HMRC by 5 October. The penalties escalate fast: a freelancer owing £8,000 who files 14 months late could face over £2,600 in penalties before interest is added.
The short version:
- Online return deadline: 31 January 2027 (for the 2025/26 tax year)
- Penalty for filing late: £100 fixed penalty, then £10 per day after three months
- Additional penalties: 5% of tax owed at six months overdue, and again at 12 months
- You can appeal a penalty if you have a reasonable excuse, such as illness or bereavement
- Register with HMRC by 5 October if you're filing self assessment for the first time
Who needs to file self assessment
You must register if you're self-employed and earned more than £1,000 in a tax year. You must also file if you have rental income, dividends, or savings interest above your personal allowance, or if your only employment is with a company you own.
You do not need to file if you're employed, have no other income, and your employer handled your tax via PAYE. Use the gov.uk decision-making tool if you're unsure.
Key dates and reportable income
The tax year runs 6 April to 5 April. You report income from that period on a return filed by 31 January the following year. Reportable income includes self-employment profit, rental income, savings interest, dividends, and freelance earnings.
Personal allowance is £12,570 for 2026/27. Income above this is taxed at 20%, rising to 40% above £50,270 and 45% above £125,140.
What happens if you miss the 31 January deadline
Penalties escalate in four stages. A freelancer owing £8,000 who files 14 months late faces £100 plus up to £900 plus £800 plus £800, easily £2,600 before interest.
| Stage | When it applies | Penalty |
|---|---|---|
| Immediate | Return filed after 31 January | £100 fixed penalty |
| After three months | Return not filed by end of April | £10 per day, up to £900 |
| After six months | Return not filed by 31 July | 5% of the tax owed |
| After 12 months | Return not filed by 31 January (next year) | 5% of the tax owed (additional) |
How to appeal and what HMRC accepts
You can appeal if you had a reasonable excuse. Valid reasons include serious illness, bereavement of a close family member, or a fire or flood affecting your records. Absence or forgetfulness will not succeed.
Appeal within 30 days of the penalty notice. Write to HMRC explaining what prevented you from filing and include evidence such as medical records or a death certificate. A successful appeal can wipe the whole penalty.
If you owe tax you cannot pay
Contact HMRC immediately. You can request a payment plan to spread the debt. If you owe £3,000 or less, HMRC can collect it through your PAYE code rather than demanding a lump sum. This does not clear any penalty.
Ignore the bill and HMRC can pursue debt recovery, including county court judgement and, in serious cases, insolvency proceedings.
The penalty escalation timeline most people miss
Most guides state the 31 January deadline and mention a £100 penalty, then stop. They omit the £10 daily charge from three months, and the 5%-of-tax-owed penalties at six and 12 months. The sting is cumulative: miss January and pay £100, miss April and pay up to £900 in daily penalties, then face 5% of your tax bill in July, then another 5% in January.
A freelancer owing £8,000 who files 14 months late faces £100 plus up to £900 plus £800 plus £800, easily £2,600 in penalties before interest. This is why the appeal route matters: a reasonable-excuse appeal can wipe the whole slate.
When to get professional help
If your income is straightforward, one self-employed business with no property or investment income, you can file alone. An accountant adds value if you have multiple income sources, rental property, or substantial expenses to claim. If you have missed the deadline, a professional can help you build a reasonable-excuse appeal quickly. Do not use an accountant to hide income or inflate expenses; that is tax evasion and carries criminal liability.
Common questions
Can I file a self assessment return late and avoid penalties?
No. A late return always incurs at least a £100 penalty. You cannot avoid it unless you appeal on grounds of reasonable excuse. File on time if at all possible.
What if HMRC says I don't have a reasonable excuse?
You can dispute their decision by requesting an internal review or by appealing to the tax tribunal. Both have strict timelines, so act quickly.
Do I pay tax on my self-employed income the moment I file?
No. Your return calculates what you owe. The balancing payment is due 31 January. If you're a repeat filer, you also make payments on account on 31 January and 31 July each year.
Can my accountant file my return after the deadline?
Yes, but late penalties still apply. The penalty is based on when the return is filed, not when your accountant received your information.
Does the penalty include interest on late tax payments?
No. Penalties and interest are separate. Interest on the tax itself runs from 1 February onwards at a rate set by HMRC. Check gov.uk for the current figure.
The complete system
the Claro guide
For the full step-by-step process, the Claro guide is the complete system to act on this.