Self Assessment deadlines: the dates that matter and what happens if you miss one
If you file a Self Assessment tax return, a handful of dates each year decide whether you pay penalties. Here they are in one place.
Key dates for a tax year
A tax year runs from 6 April to 5 April. For the return covering that year:
- 5 October — tell HMRC if you need to register for Self Assessment for the first time.
- 31 October — deadline for paper returns.
- 31 January — deadline for online returns and for paying any tax owed.
- 31 July — second payment on account, if you make them.
If you miss the filing deadline
You get a £100 penalty if your return is up to three months late, even if you owe no tax. Further penalties apply the longer it stays late. Paying late also adds interest and can bring separate late payment penalties.
Reading a reminder letter
HMRC sends reminders and a 'notice to file'. Check which tax year it refers to — a common mistake is confusing the year the return covers with the year it is due. If you think you no longer need to file, tell HMRC rather than ignoring the notice.
If you can't pay in full
You may be able to set up a payment plan with HMRC. It is better to file on time and arrange payment than to delay filing.
Published 26 October 2026. This guide is general information, not legal or financial advice. Rules can change and may differ across the UK — check the official sources below for your situation.
Sources
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