Self Assessment 2025/26: the dates you need to know

The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. If you need to complete a Self Assessment tax return for that year, here are the dates to put in your diary.

The key dates

• 5 October 2026 — the deadline to tell HMRC you need to file, if you are newly self employed or have new income to declare.
• 31 October 2026 — the deadline if you file a paper tax return.
• 31 January 2027 — the deadline to file your return online, and to pay any tax you owe for 2025/26.
• 31 January 2027 — also the date your first payment on account for the next year may be due.
• 31 July 2027 — the date any second payment on account is due.

What happens if you are late

HMRC charges penalties even if you owe no tax:

• An automatic £100 penalty as soon as you miss the online filing deadline.
• Daily penalties if your return is more than three months late.
• Further penalties and interest on top if tax is paid late.

The good news is that these are completely avoidable with a little planning.

How to stay ahead

• Gather your income and expense records early, rather than in January.
• Register in good time if it is your first return.
• Better still, hand it to us and we will prepare, check and file it well before the deadline.

Penalties for missing the deadline

Missing the filing deadline triggers an automatic penalty of 100 pounds, even if you have no tax to pay or you have already paid it. If the return is still outstanding after 3 months, HMRC adds 10 pounds a day for up to 90 days, which is a further 900 pounds. At 6 months and again at 12 months you face another penalty of 5 per cent of the tax due or 300 pounds, whichever is higher. The penalties stack, so a return that is a year late can cost well over 1,600 pounds before the tax itself.

Late payment penalties and interest

Paying late is treated separately from filing late. If tax for the year is still unpaid 30 days after the 31 January deadline you are charged 5 per cent of the amount outstanding, with the same charge again at 6 months and at 12 months. On top of that, interest runs daily on anything paid late, so it pays to clear the balance as soon as you can.

Payments on account

If your last bill was 1,000 pounds or more, you usually also make two payments on account towards next year. The first is due on 31 January alongside your balancing payment, and the second on 31 July, each one being half of your previous year tax. These catch a lot of people out in their first full year, so it is worth setting the money aside early.

How to make sure you never miss it

The simplest way to stay safe is to register early, file early and pay early. Get your unique taxpayer reference and your Government Gateway login sorted well before January, keep your income and expense records as you go rather than in a last minute rush, and aim to file in the autumn so any tax due is no surprise. If you would rather not think about it at all, we can take the whole return off your hands and make sure every deadline is met.