Would you rather someone else handled this? Our Self Assessment service means we prepare, check and file your tax return with HMRC on a fixed fee.
The dates for the 2025/26 tax year
The 2025/26 tax year ended on 5 April 2026. Here is what you are working towards.
5 October 2026 is the deadline to register if this is your first return. Miss it and you are into failure to notify territory, which is a percentage of the tax rather than a flat fee.
31 October 2026 is the paper filing deadline. Almost nobody should be filing on paper, but if you are, this is your date and it is three months earlier than the online one.
30 December 2026 matters if you want tax collected through your PAYE code rather than paid in a lump. It only works if you owe under £3,000 and you already have a PAYE source. Miss this date and the option is gone for the year.
31 January 2027 is the big one: online filing, the balancing payment for 2025/26, and the first payment on account for 2026/27, all due the same day.
31 July 2027 is the second payment on account.
The January trap nobody warns you about
First time filers are routinely caught by this. On 31 January you may be paying two things at once: the tax you owe for the year just gone, plus the first instalment towards next year, which is typically half of last year total.
So a first bill of £4,000 can arrive as £6,000 in January and another £2,000 in July. Nobody told you, and the money is not there. This is the single most common reason a new self employed person has a very bad January.
If your income has genuinely dropped, you can apply to reduce your payments on account. Be careful, because if you reduce them too far HMRC charges interest on the shortfall.
What late actually costs
A day late is £100, whether or not you owe any tax. Three months late and daily penalties of £10 a day start, capped at £900. Six months adds 5% of the tax due or £300, whichever is greater, and twelve months adds the same again.
Late payment is separate from late filing and interest runs on top. HMRC late payment interest is currently 7.75%, which is not a trivial number on a real bill.
The advice that actually helps
File early, pay late. There is no reason those are the same event. Filing in May tells you exactly what you owe nine months before you have to pay it, which is nine months to put the money aside. People conflate the two and file in January purely because that is when payment is due.
If you cannot pay, talk to HMRC before the deadline rather than after. A Time to Pay arrangement is a normal thing that ordinary businesses use, and it is considerably easier to agree before you have defaulted.
These dates are for the 2025/26 return and reflect HMRC guidance. If you want yours done early rather than in the January scramble, get in touch.
Related services and guides
Deadline Centre Self Assessment service Deadlines & penalties guide