Money

Self Assessment Tax Returns in the UK: Who Must File and When

2 min read

In this guide
  1. Quick answer
  2. When do you fill it in?
  3. Key dates
  4. What records should you keep?
  5. Common mistakes
  6. FAQ
    1. Do employees need one?
  7. Key takeaways
  8. Related guides
  9. Sources

A Self Assessment tax return is how HMRC collects Income Tax from people whose income is not fully taxed at source. Newcomers who become self-employed, rent out property or have foreign income often hit this system by surprise. This guide covers the basics, based on GOV.UK.

Quick answer

  • Tax on wages and pensions is usually deducted automatically; other income must be reported in a return.
  • You must send a return if HMRC asks you to, or if you were a sole trader earning more than £1,000 before expenses.
  • Tell HMRC by 5 October if you need a return for the previous tax year and have not filed before.
  • Pay your bill by 31 January.

When do you fill it in?

After the end of the tax year it applies to, which ends on 5 April. You can file online. If you need a paper form, download the SA100 or call HMRC to ask for one.

Key dates

Date What
5 April End of the tax year
5 October Tell HMRC you need to file, if new to Self Assessment
31 January Pay your Self Assessment bill

You may be fined if you do not tell HMRC by 5 October, and you can face interest and a penalty if you file or pay late.

What records should you keep?

Keep records such as bank statements and receipts so you can complete the return correctly. HMRC works out what you owe from what you report, and the amount depends on your Income Tax band. A different rate applies to Capital Gains Tax, for example when you sell shares or a second home.

Common mistakes

  • Missing the 5 October registration deadline.
  • Waiting for HMRC to remind you.
  • Throwing away receipts.

FAQ

Do employees need one?

Not usually, unless they have other income or HMRC asks. See UK Income Tax rates.

Key takeaways

  • Register early.
  • Keep records.
  • Pay by 31 January.

Last updated: October 2026. General information, not tax advice. Confirm with HMRC.

Sources

  • GOV.UK: Self Assessment tax returns

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