Missing a self assessment deadline costs money. HMRC's penalty system is automatic and largely merciless — it does not matter whether you owe any tax or not. Miss the filing deadline and the £100 fine arrives regardless.
The good news is the deadlines are predictable. Here is a complete guide for the 2025/26 tax year, with all the key dates in one place.
Key dates for 2025/26
The new tax year begins. Income, gains, and allowances reset. Good time to review your tax position for the year ahead.
If you made payments on account, the second instalment is due. This is based on your 2023/24 tax liability. If your income has dropped, you can apply to reduce it.
If you need to file a return for 2024/25 for the first time — because you became self-employed, received rental income, or had other untaxed income — you must register by this date.
If you are submitting a paper self assessment return (rather than filing online), this is your deadline. Most people file online, in which case this does not apply.
The most important date. Your 2024/25 self assessment return must be filed online. Any tax owed for 2024/25 must be paid. Your first payment on account for 2025/26 is also due on the same day.
The tax year closes. Ensure any year-end planning — pension contributions, ISA allowances, capital gains — is completed before midnight.
What are payments on account?
Payments on account are advance payments toward your next year's tax bill. HMRC requires them from anyone whose self assessment tax liability exceeds £1,000, and where less than 80% of their tax is collected at source (i.e. through PAYE).
Each payment on account is half of your previous year's tax liability, paid in two instalments — January 31st and July 31st. If your income increases, you may owe a balancing payment on top. If it decreases, you may be owed a refund.
You can apply to reduce your payments on account if you know your income will be lower this year. This is done through HMRC's online portal or through your accountant. Do not just not pay — that leads to interest charges regardless of whether the reduction was justified.
The penalty structure — what happens if you miss deadlines
1 day late: Automatic £100 penalty — even if you have no tax to pay
3 months late: £10 per day for up to 90 days (maximum £900 additional)
6 months late: Further penalty of 5% of tax owed, or £300, whichever is higher
12 months late: Another 5% of tax owed or £300 — and potentially higher penalties if HMRC believes the delay was deliberate
Late payment: Interest at HMRC's official rate (currently above 7%) from the due date, plus surcharges for payments more than 30 days late
HMRC can waive penalties in cases of genuine reasonable excuse — serious illness, bereavement, or system failures on HMRC's side have all been accepted. Simply forgetting or being disorganised is not considered a reasonable excuse.
Common reasons people miss deadlines
- Waiting for documents: P60s, interest statements, dividend vouchers, and other documents can arrive late. Do not wait until January — start gathering them in April
- Not registered in time: If you became self-employed in 2024/25 and have not registered with HMRC, you need to do so before October 5th
- Forgetting the July payment: The July 31st payment on account catches people out because it falls in summer and is easy to overlook
- Assuming a zero liability means no return needed: If HMRC has issued you a notice to file, you must file — even if you owe nothing
- UTR not to hand: Your Unique Taxpayer Reference is needed to file. If you have lost it, allow several weeks to retrieve it from HMRC
Do you need to file a self assessment return?
You normally need to file if you:
- Were self-employed and earned more than £1,000
- Received income from property rental
- Had income over £100,000
- Received dividends or savings interest above your allowances
- Made capital gains above the annual exempt amount
- Received Child Benefit and either you or your partner earned over £60,000
- Have foreign income or are a company director
If you are unsure whether you need to file, it is always worth checking. Failing to register when required carries its own penalties.
Self assessment handled for you
We prepare and submit self assessment returns for sole traders, directors, and individuals — on time, every time. No January panic, no missed deadlines.
Get StartedThis article is for general information purposes. Deadlines and penalty amounts are correct as of March 2026. HMRC rules can change — always verify current deadlines on gov.uk or with your accountant.