Self Assessment deadlines and penalties for 2025 to 2026

Deadlines for the 2025 to 2026 tax year

	Date	Notes
Register for Self Assessment	5 October 2026	For a first return or after a year off (GOV.UK)
Paper return	31 October 2026	HMRC must receive it by 11:59pm (GOV.UK)
Online return to have tax collected through the tax code	30 December 2026	Submit by 11:59pm
Online return	31 January 2027	Submit by 11:59pm
Balancing payment and first payment on account	31 January 2027	Pay by 11:59pm
Second payment on account	31 July 2027	For the 2026 to 2027 tax year

Registering late

GOV.UK says that where someone registers after 5 October 2026, HMRC sends a letter or email with a different deadline, which will be 3 months from the date on the letter or email.

Late filing penalties

1 day late: an initial £100 penalty (GOV.UK: penalties).
3 months late: daily penalties of £10 a day, up to £900.
6 months late: a further penalty of 5% of the tax due or £300, whichever is greater.
12 months late: another 5% of the tax due or £300, whichever is greater.

Late payment penalties

30 days after the due date: 5% of the tax unpaid at that date (GOV.UK: penalties).
6 months: a further 5% of the tax unpaid at that date.
12 months: a further 5% of the tax unpaid at that date.

Interest

Interest is charged on tax paid late, alongside any penalty. HMRC's interest rates page gives the late payment rate as 7.75% from 9 January 2026. It is set at the Bank of England base rate plus 4%, the margin that has applied since 6 April 2025, so it moves when the base rate changes. The same page gives the repayment interest rate as 2.75% from 9 January 2026, set at base rate minus 1% with a lower limit of 0.5%.

Paying and appealing penalties

GOV.UK says a penalty must be paid within 30 days of the date on the penalty notice. A client with a reasonable excuse can appeal. HMRC also has an online tool to estimate the penalty for a late return or late payment.

Worked example

For example, a client files their 2025 to 2026 return on 15 August 2027 with £4,000 of tax due, paid on the same day. Applying the GOV.UK penalty rules, the return is more than 6 months late: £100, plus £900 in daily penalties, plus £300 at 6 months because 5% of £4,000 is £200 and £300 is greater. The late filing penalties total £1,300.

The tax was also unpaid 30 days and 6 months after 31 January 2027, so two late payment penalties of 5% apply, £200 each, plus interest from 31 January 2027 to the date paid.

Interest runs for 196 days. At the 7.75% rate on HMRC's interest rates page, if it stays unchanged, that is £4,000 × 7.75% × 196 ÷ 365, which is £166.47. The total cost of filing and paying late in this example is £1,300 in filing penalties, £400 in payment penalties and £166.47 in interest.

Questions

Is the payment deadline the same for a paper return?

Yes. GOV.UK gives one payment deadline of 11:59pm on 31 January 2027, whichever way the return is sent.

What happens to a paper return received after 31 October?

It is late, and GOV.UK says a late filing penalty follows. The client can still file online by 31 January 2027 to meet the online deadline.

When can tax be collected through the tax code?

When the online return is submitted by 30 December 2026, according to GOV.UK.

Is there a penalty for registering late?

GOV.UK's registration page says a person who tells HMRC after 5 October 2026 could get a penalty. HMRC then sets a filing deadline 3 months from the date of its letter or email.

Do penalties change under Making Tax Digital for Income Tax?

Clients in Making Tax Digital for Income Tax come under a different penalty system. See Making Tax Digital for Income Tax penalties.

In Accountin

In Accountin, the deadlines dashboard lists each client's 31 January Self Assessment date with who looks after the client, alongside their other deadlines.