Self Assessment deadlines and penalties
The Self Assessment calendar barely changes from year to year, which makes it easy to plan around, and easy to forget. Here are the dates that matter and what happens if you miss them.
The key dates
| Deadline | What it's for |
|---|---|
| 5 October | Register for Self Assessment (if it's your first year) |
| 31 October (midnight) | File a paper return |
| 31 January (midnight) | File your online return and pay the tax due |
| 31 July | Second payment on account (if you make them) |
The tax year itself runs from 6 April to 5 April. So the 2024-25 tax year ended on 5 April 2025, and the online return and payment for it are due by 31 January 2026.
Registering
If you're newly self-employed or need to file for the first time, you must tell HMRC by 5 October following the end of the tax year in which the income arose. Registering can take a little time because HMRC posts out your Unique Taxpayer Reference, so don't leave it to the last week.
The two things due on 31 January
It's worth stressing that 31 January is both the filing deadline and the payment deadline. Filing on time but paying late still triggers interest. If you also make payments on account, the first one is due on this date too, on top of the balancing payment for the year just filed.
Penalties for filing late
- 1 day late: an automatic £100 penalty, even if you owe no tax.
- 3 months late: £10 a day, up to £900, on top of the £100.
- 6 months late: a further penalty of 5% of the tax due or £300, whichever is greater.
- 12 months late: another 5% or £300, and in serious cases more.
Penalties for paying late
Late payment attracts interest from 1 February, plus separate late-payment penalties at 30 days, 6 months and 12 months. If you genuinely can't pay in full, contacting HMRC to arrange a Time to Pay plan is far better than simply missing the payment. It can head off the penalties.
Know the number early
You don't have to wait until you file to know what you'll owe. Once the tax year ends on 5 April, put your figures into the estimator and you'll have a solid estimate straight away, plenty of time to set the money aside before the January deadline.