Missing a Self Assessment deadline can trigger an immediate £100 fine — even if you owe no tax at all. Here are all the dates that matter for the 2024/25 tax year (filed and paid in 2025 and 2026), plus what happens if you miss them.
Who needs to file a Self Assessment return?
You need to file a Self Assessment return if, in the 2024/25 tax year (6 April 2024 to 5 April 2025), any of the following applied to you:
- You were self-employed as a sole trader and earned more than £1,000
- You were a partner in a business partnership
- You had untaxed income above £2,500 (e.g. rental income, savings interest)
- Your income was over £100,000
- You received dividends from shares that take you into a higher tax band
- You claimed Child Benefit and either you or your partner earned over £60,000
- You are a company director (unless your only income is PAYE salary with no dividends)
If you're not sure, HMRC has a quick tool at gov.uk/check-if-you-need-tax-return.
The key deadlines at a glance
| Deadline | Date | What it covers |
|---|---|---|
| Register for Self Assessment | 5 October 2025 | If 2024/25 is your first year, you must tell HMRC by this date |
| Paper return deadline | 31 October 2025 | Last date to file a paper SA return for 2024/25 |
| Online return + tax payment | 31 January 2026 | File your 2024/25 return online and pay any tax owed |
| First payment on account | 31 January 2026 | 50% advance payment towards 2025/26 tax bill |
| Second payment on account | 31 July 2026 | Remaining 50% advance payment towards 2025/26 tax bill |
| 2025/26 online return deadline | 31 January 2027 | File your 2025/26 return and pay any balancing payment |
What are payments on account?
Payments on account are advance payments towards your next year's tax bill. HMRC requires them if your Self Assessment tax bill is more than £1,000, and less than 80% of your tax was collected at source (e.g. via PAYE).
Each payment on account is 50% of your previous year's total tax bill. So if your 2024/25 tax bill was £4,000, you'd pay £2,000 on 31 January 2026 and another £2,000 on 31 July 2026 — both as advance payments toward your 2025/26 bill.
If you know your income will be lower next year, you can apply to reduce your payments on account through your HMRC online account. However, if you reduce them too much, HMRC will charge interest on the difference.
What are the penalties for filing late?
Late filing penalties build up quickly:
- 1 day late: £100 automatic penalty (regardless of whether you owe tax)
- 3 months late: £10 per day, up to a maximum of £900
- 6 months late: A further 5% of the tax due (or £300, whichever is higher)
- 12 months late: Another 5% of tax due (or £300) — and potentially higher penalties if HMRC considers it deliberate
Late payment of tax also incurs interest (currently 7.25% per annum) plus a 5% surcharge if unpaid after 30 days, six months, and twelve months.
Can I get an extension?
HMRC does grant extensions in cases of genuine hardship or exceptional circumstances — for example bereavement or serious illness. However, you need to contact HMRC proactively before the deadline, not after. You can appeal a penalty if you have a reasonable excuse, but routine reasons like "I forgot" or "I was too busy" are not accepted.
Making Tax Digital (MTD) — what's coming
From April 2026, Making Tax Digital for Income Tax begins to roll out. Self-employed people and landlords with income above £50,000 will be required to keep digital records and submit quarterly updates to HMRC using compatible software, rather than filing a single annual return. The threshold drops to £30,000 from April 2027. This is a significant change — check HMRC's MTD guidance if your income is in this range.