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The deadlines

• Paper return: HMRC must receive it by 11:59pm on 31 October 2026 or you will get a late filing penalty.
• Online return: you must submit it by 11:59pm on 31 January 2027 or you will get a late filing penalty. You can submit any time on or after 6 April 2026.
• Paying the tax you owe: by 11:59pm on 31 January 2027 or you will get a penalty. There is a second payment deadline of 31 July if you make payments towards your bill (known as payments on account).
• If you want to pay your bill through your tax code, you must submit your online return by 11:59pm on 30 December 2026. If you miss this, you will have to pay another way.
• 31 January 2027 falls on a Sunday. The deadlines page does not mention any extension for weekends, so do not count on Monday.
• Source: GOV.UK: Self Assessment deadlines. The page also says HMRC must receive your return and any money you owe by the deadline.

Who needs to send a return

• The GOV.UK page says you must send a tax return if, in the last tax year (6 April to 5 April), any of these applied: you were self-employed as a sole trader and earned more than £1,000 (before taking off anything you can claim tax relief on); you were a partner in a business partnership; you had to pay Capital Gains Tax; you had to pay the High Income Child Benefit Charge and do not pay it through PAYE; or you are an off-payroll worker repaying a student or postgraduate loan.
• You may also need to send one if you have untaxed income, such as money from renting out property or land, tips and commission, savings interest, dividends (including investments), foreign income, or any taxable UK income if you are a non-UK resident.
• You must also send a return if HMRC asks you to. If you are not sure, GOV.UK has a tool, Check if you need to send a Self Assessment tax return, which says it does not send your details to HMRC. If you believe you no longer need to send a return, you need to contact HMRC and explain this.
• Source: GOV.UK: Who must send a tax return.

What counts as the tax year

• The UK tax year runs from 6 April to 5 April. The return due in January 2027 is for the tax year that started on 6 April 2025 and ended on 5 April 2026.
• If you moved to or left the UK part-way through, the page does not give a separate rule in the sections we read. Check the GOV.UK pages or ask a qualified adviser about your own case.
• Source: GOV.UK: Deadlines.

Registering: the 5 October date has passed

• GOV.UK says you must tell HMRC by 5 October 2026 if you need to complete a tax return for the previous tax year and you have not sent a tax return before, or you registered before but did not need to send a return for 2024 to 2025. You tell HMRC by registering for Self Assessment.
• Today is after that date. The deadlines page says that if you register after 5 October 2026, HMRC will send you a letter or email with a different deadline to send your return, which will be 3 months from the date on the letter or email. You must still pay the tax you owe by 11:59pm on 31 January 2027 or you will get a penalty.
• If you tell HMRC after 5 October 2026, you could get a penalty. If you are waiting for a Unique Taxpayer Reference (UTR), the registration page links to a way to check when you can expect a reply from HMRC.
• Before you register, check if you need to send a tax return. Start here: GOV.UK: Check how to register for Self Assessment.

Penalties

• Late filing: an initial £100 penalty; after 3 months, additional daily penalties of £10 per day, up to a maximum of £900; after 6 months, a further penalty of 5% of the tax due or £300, whichever is greater; after 12 months, another 5% or £300 charge, whichever is greater.
• Late payment: penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months. You will also be charged interest on the amount owed.
• Registering late: if you register after 5 October and do not pay all of your tax bill by 31 January, you may get a "failure to notify" penalty, based on the amount still left to pay.
• You must pay a penalty within 30 days of the date on the penalty notice. If you have a reasonable excuse, you can appeal against a penalty.
• Source: GOV.UK: Self Assessment penalties.

A practical order for newcomers

• Use the GOV.UK check tool to see whether you need a return for 6 April 2025 to 5 April 2026.
• If you have not registered and need to, do it now rather than waiting: the registration date has passed.
• Keep records such as bank statements or receipts so you can fill in the return correctly (the overview page says you need to keep records).
• Aim to file and pay well before Sunday 31 January 2027. You can estimate your tax bill on GOV.UK before sending your return.
• Overview of the whole process: GOV.UK: Self Assessment tax returns.

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Frequently asked questions

• What is the Self Assessment deadline in January 2027? HMRC must receive your online tax return and any tax you owe by 11:59pm on 31 January 2027. A paper return must arrive by 11:59pm on 31 October 2026.
• Is 31 January 2027 a weekday? No, it is a Sunday. The GOV.UK deadlines page does not state a later date, so plan to file and pay earlier.
• Which tax year is the January 2027 return for? The tax year that started on 6 April 2025 and ended on 5 April 2026.
• Who must send a Self Assessment return? GOV.UK lists, among others, sole traders who earned more than £1,000, partners in a business partnership, people who had to pay Capital Gains Tax, and people who must pay the High Income Child Benefit Charge outside PAYE. Untaxed income such as rent, foreign income or taxable UK income as a non-UK resident may also mean you need one.
• I have not registered. Is it too late? The 5 October 2026 date has passed. GOV.UK says that if you register after it, HMRC will give a different filing deadline, 3 months from the date on its letter or email, but you must still pay by 31 January 2027, and you could get a penalty.
• What is the late filing penalty? An initial £100, then daily penalties of £10 per day after 3 months up to £900, then 5% of the tax due or £300 (whichever is greater) after 6 months and again after 12 months.

Sources

• GOV.UK: Self Assessment deadlines
• GOV.UK: Who must send a tax return
• GOV.UK: Check if you need to send a Self Assessment tax return
• GOV.UK: Check how to register for Self Assessment
• GOV.UK: Self Assessment penalties
• GOV.UK: Self Assessment tax returns (overview)

Last checked 26 October 2026. General information, not tax advice: check gov.uk or ask a qualified adviser. Rules and dates can change.