Self Assessment deadlines: key dates and what you need to file

Who needs to send a Self Assessment tax return?

Most employees and pensioners pay their tax through PAYE and never need a return. You must send one if, in the last tax year, you were a sole trader earning more than £1,000 before tax relief, a partner in a business partnership, or you owed Capital Gains Tax on something you sold.

You also need one if you had to pay the High Income Child Benefit Charge and did not pay it through PAYE. Untaxed income, such as rent from a property, tips, commission, dividends, savings interest or foreign income, can also mean a return. If HMRC writes asking you to file, you must do so even if you think you owe nothing.

What are the Self Assessment deadlines?

Every date below relates to the tax year that has just ended. For the 2025 to 2026 tax year, which ended on 5 April 2026, the dates fall between October 2026 and January 2027. You can file from 6 April, and sending early does not mean paying early: you still pay by 31 January.

• 5 October: tell HMRC you need a return if you have not sent one before, or did not need one last year.
• 31 October: paper returns must reach HMRC by this date.
• 30 December: file online by this date if you want a bill under £3,000 collected through your PAYE tax code.
• 31 January, 11:59pm: online returns must be submitted and any tax owed paid, including your first payment on account.
• 31 July: your second payment on account is due.

What if you register late?

If you register after 5 October, HMRC gives you a return deadline of three months from the date on its letter or email. The tax itself is still due by 31 January, so registering late does not move the payment date.

If you register late and do not pay your full bill by 31 January, you may also face a failure to notify penalty, based on the tax left unpaid. Register as soon as you know you need to, even if you are unsure of the figures.

How do payments on account work?

Payments on account are advance payments towards next year's bill, including Class 4 National Insurance if you are self-employed. Each one is normally half of the tax you owed the year before, paid by 31 January and 31 July.

You do not have to make them if last year's Self Assessment bill was under £1,000, or if more than 80% of your tax was already taken at source, such as through your tax code. If you earn more than expected, a balancing payment is due by the next 31 January.

Your first year is often the biggest shock. You pay the full bill for the year plus your first payment on account for the next one, all on the same January date. If you expect a lower bill, you can ask HMRC to reduce your payments on account online or with form SA303, but you will be charged interest if you reduce them too far.

What are the penalties for filing or paying late?

Late filing penalties apply even if you owe no tax or pay on time. Late payment penalties and interest are separate and come on top. These are the rules on GOV.UK today, and you can appeal if you had a reasonable excuse.

• Return 1 day late: a fixed penalty of £100.
• After 3 months: £10 for each day, up to £900.
• After 6 months: a further 5% of the tax due or £300, whichever is more.
• After 12 months: another 5% or £300, whichever is more.
• Tax paid late: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest.

What records should you keep?

Keep everything that supports the figures on your return: sales and income, invoices, receipts for expenses, bank statements, rent statements, P60s and P11Ds, pension contributions and gift aid donations. Digital copies are fine as long as they are clear and complete.

If you are self-employed, keep records for at least 5 years after the 31 January deadline for that tax year. For a 2025 to 2026 return filed by 31 January 2027, that means keeping them until at least the end of January 2032. If records are lost, give your best figures and tell HMRC they are estimated or provisional.

How does Making Tax Digital for Income Tax change things?

Making Tax Digital for Income Tax applies to sole traders and landlords. Whether you must join depends on your qualifying income: your gross income from self-employment and property before expenses, not your profit. Employment income, dividends, pensions and your share of partnership profit do not count.

If your qualifying income was over £50,000 in the 2024 to 2025 tax year, you should have started from 6 April 2026. Over £30,000 in 2025 to 2026 means starting from 6 April 2027, and over £20,000 in 2026 to 2027 means starting from 6 April 2028. HMRC checks your Self Assessment return each year to see if you qualify.

Once you are in, you keep digital records in compatible software and send quarterly updates. The standard deadlines are 7 August, 7 November, 7 February and 7 May. You still submit a tax return through your software after the year ends. For the 2026 to 2027 tax year, late quarterly updates do not earn penalty points, but late returns do. Check the current rules on GOV.UK, as details can change.

How AYS can help

On AYS you can describe your situation and receive free quotes from local accountants, with no obligation. Say what income you have, which tax years are involved and how your records are kept, and book the accountant who fits well before the deadline.

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