Self Assessment · 2023/24
Self Assessment 2023/24 — Deadlines, Penalties, How to File
The 2023/24 tax year ran from 6 April 2023 to 5 April 2024. The online filing and payment deadline is 31 January 2025; if you file on paper using SA100, the earlier deadline is 31 October 2024.
HMRC issues an automatic £100 penalty the day after the deadline — even if you owe nothing or are due a refund. Daily £10 charges start 3 months later. Pay any tax due by the same date to avoid interest at Bank of England base rate + 4%.
Key dates for 2023/24
| Tax year start | 6 April 2023 |
| Tax year end | 5 April 2024 |
| Register for SA (first-time filers) | 5 October 2024 |
| Paper return (SA100) deadline | 31 October 2024 |
| Online return + balancing payment + 1st payment on account | 31 January 2025 |
| 2nd payment on account | 31 July 2025 |
| Refund / amendment deadline (4-year rule) | 5 April 2028 |
How to file your 2023/24 return
- Register if it is your first time. New filers must register on gov.uk by 5 October 2024. HMRC posts your UTR within 10 working days, then a separate activation code for the online service.
- Gather paperwork. P60, P45s, P11D, bank/building society interest, dividend vouchers, rental records, self-employment income and expenses, pension contributions, Gift Aid, and any foreign income for the year 6 April 2023 – 5 April 2024.
- Log in via Government Gateway. Go to gov.uk/log-in-file-self-assessment-tax-return and authenticate with two-factor (HMRC app or SMS code).
- Complete the right supplementary pages:
- SA102 — employment income (P60/P45/P11D).
- SA103 — self-employment.
- SA105 — UK property.
- SA106 — foreign income and gains.
- SA108 — capital gains.
- Check payments on account. If the bill is over £1,000 and PAYE covers less than 80%, HMRC sets two equal payments due 31 January 2025 and 31 July 2025. Use form SA303 to reduce them if your next-year income will fall.
- Submit. Online by 31 January 2025 or paper SA100 by 31 October 2024. Save the on-screen submission receipt.
- Pay the tax. Faster Payments, debit card, Direct Debit or at your bank — all must clear HMRC by 31 January 2025 to avoid interest.
- Keep records for at least 5 years after the filing deadline (6 years if self-employed). HMRC can open an enquiry up to 12 months after submission.
Penalty timeline for 2023/24
Penalties stack and apply even if no tax is due. Dates below assume you missed the online deadline of 31 January 2025:
| From | Trigger | Charge |
|---|---|---|
| 1 February 2025 | 1 day late (automatic) | £100 fixed |
| 2 May 2025 | 3 months late | £10 per day, capped at £900 |
| 31 July 2025 | 6 months late | £300 or 5% of tax due, whichever is greater |
| 31 January 2026 | 12 months late | Another £300 or 5% (higher in deliberate cases) |
Late-payment interest runs from 1 February 2025 at Bank of England base rate + 4%. A 5% surcharge on unpaid tax is added at 30 days, 6 months and 12 months. Full table at gov.uk/self-assessment-tax-returns/penalties.
Get your refund if you overpaid 2023/24
If your 2023/24 return overstated tax (or you missed an allowance, expense or pension relief), you can amend the return within 12 months of the filing deadline, or claim overpayment relief up to 5 April 2028 under the 4-year rule. See our 2023/24 refund guide for the exact form and process.
Estimate your 2023/24 tax
For period-accurate figures see the 2023/24 tax rates reference.