Self Assessment deadlines: what you need to know
If you're self-employed, a partner in a business, a landlord, or otherwise need to file a Self Assessment tax return, missing a deadline can mean an automatic penalty, even if you don't owe any tax. Here are the dates that actually matter.
At a glance
- New filers must register for Self Assessment by 5 October following the end of the tax year.
- Online returns, and any balance owed, are due by 31 January.
- A £100 penalty applies from one day late, even if no tax is owed.
- "Payments on account" can make your January bill larger than just one year's tax.
The headline dates for the 2025/26 tax year
- 5 October 2026: deadline to register for Self Assessment if you need to file a return for the first time and haven't already registered.
- 31 October 2026: deadline for paper tax returns.
- 31 January 2027: deadline for online tax returns, the deadline to pay any remaining balance owed for 2025/26 (your "balancing payment"), and the deadline for your first payment on account towards 2026/27, if you're required to make them.
- 31 July 2027: deadline for your second payment on account towards 2026/27, if applicable.
Registering after 5 October? You can still register: HMRC will give you a revised deadline, typically three months from the date you register. It's better to register as early as possible either way.
What "payments on account" actually mean
If your last Self Assessment bill was over £1,000 (and less than 80% of it was already collected at source, e.g. through PAYE), HMRC usually asks you to pay next year's tax in advance, in two instalments, each normally half of your previous year's tax bill. That means the 31 January payment can be three amounts bundled into one: the balance for the year just ended, plus the first instalment towards the year ahead. It's the single biggest reason people are caught out by a January bill larger than they expected.
What happens if you miss the deadline
Filing even one day late triggers an automatic £100 penalty, regardless of whether you owe tax or are due a refund. Further daily penalties apply after three months, with additional fixed and tax-geared penalties after six and twelve months. Interest also accrues on any tax paid late.
Why leaving it early makes a real difference
Filing well before January doesn't just avoid the risk of a last-minute technical problem or missing paperwork; it also means you know what you owe with plenty of time to plan for the payment, rather than finding out in the final days of January.
This article is general information, not personal tax advice, and deadlines can change; always check your specific position. Get in touch if you'd like help getting your return filed early.