Self Assessment deadlines and penalties
Last updated: 13 October 2026
Who has to send a return, the 2025/26 and 2026/27 deadlines, late-filing penalties, and how payments on account are split.
Who has to send a return
GOV.UK’s current “who must send a tax return” page lists a short set of cases for the last tax year, which runs from 6 April to 5 April. You must send a return if you were self-employed as a sole trader and earned more than £1,000 before expenses, if you were a partner in a business partnership, if you had to pay Capital Gains Tax on a disposal, if you had to pay the High Income Child Benefit Charge and do not pay it through PAYE, or if you are an off-payroll worker repaying a student or postgraduate loan.
You may also need a return for untaxed income. The same page names rent, tips and commission, savings interest, dividends, foreign income, and taxable UK income if you are not UK resident. Wanting to claim some venture-capital reliefs can be a reason too. You can also choose to file, for example to prove self-employment for Tax-Free Childcare or Maternity Allowance, or to pay voluntary National Insurance. If you are unsure, GOV.UK’s checker is the thing to use. This page does not add a salary threshold that the current “who must send” list does not print.
The dates for 2025/26 and 2026/27
The live deadlines page is written for the tax year that started on 6 April 2025 and ended on 5 April 2026. If you need to file for that year and you have not sent a return before, or you registered before but did not need one for 2024/25, you must tell HMRC by 5 October 2026. A paper return must reach HMRC by 11:59pm on 31 October 2026. An online return must be submitted by 11:59pm on 31 January 2027. The tax is due by the same January deadline. If you want the bill collected through your tax code, the return has to be in by 11:59pm on 30 December 2026.
Registering after 5 October 2026 does not move the payment date. HMRC will give you a later filing date, three months from the letter or email, but the tax for that return is still due by 11:59pm on 31 January 2027. The same timetable, shifted one year, is how the following return works: tell HMRC by 5 October 2027 if 2026/27 is a new filing year, paper by 31 October 2027, online filing and payment by 31 January 2028, and 30 December 2027 if you want that bill in a later tax code. The deadlines page describes the pattern for “the last tax year” rather than reprinting 2028, so the 2026/27 dates here are that pattern applied to the year that runs from 6 April 2026 to 5 April 2027.
Payments on account
Payments on account are two instalments towards the next bill, including Class 4 National Insurance if you are self-employed. Each one is half of the tax you owed last year. They are due by midnight on 31 January and 31 July. You do not have to make them if last year’s tax was less than £1,000, or if more than 80% of last year’s tax was paid outside Self Assessment, for example through a tax code.
GOV.UK’s worked case is a £3,000 bill for 2023/24, with two earlier payments on account of £900. The balancing payment on 31 January 2025 is £1,200, and the first payment on account towards the next year is another £1,500, so £2,700 is due that day. The second £1,500 follows on 31 July 2025. The same arithmetic applies to a later year. A 2025/26 bill of £2,000 produces payments on account of £1,000 on 31 January 2027 and £1,000 on 31 July 2027, if neither of the exemptions applies. That £1,000 split is half of £2,000. It is not a second official example.
If you know the next year will be smaller, you can ask HMRC to reduce the payments, online or on form SA303. If you reduce them and the bill comes in higher, interest is charged on the difference. A balancing payment can also include capital gains and, if you are self-employed, student-loan amounts. The income tax calculator estimates income tax on profits or salary for 2026/27. It does not compute payments on account, Class 2 or Class 4 National Insurance, or a student-loan plan.
Penalties and interest
The Self Assessment penalties page charges an initial £100 if the return is late. After three months it adds £10 a day, up to £900. After six months it adds 5% of the tax due or £300, whichever is greater. After twelve months it adds another 5% or £300, whichever is greater. A late partnership return is charged to each partner.
Late payment is a separate penalty: 5% of the tax unpaid at 30 days, again at six months, and again at twelve months, plus interest. HMRC’s compliance handbook says those late-payment penalties apply to the balancing payment, not to the payments on account themselves. Interest still runs on a late payment on account. If you register after 5 October and the tax is not paid by 31 January, a failure-to-notify penalty can be based on what is still unpaid.
Making Tax Digital volunteers are on a different late-payment table, published separately. Someone who volunteers from 6 April 2026 still has the current penalties for the 2025/26 return due on 31 January 2027. This guide follows the standard Self Assessment penalties page for everyone else, and it does not copy the volunteer percentages across. A penalty can be appealed if you have a reasonable excuse. The appeal has to be made; missing the date and waiting is not itself the excuse.