Self Assessment checklist before 31 January 2027

The online deadline for 2025/26 returns, and for paying any tax owed, is 31 January 2027. Work through this list in order.

  1. Registered? If you started a side hustle in 2025/26 and earned over £1,000, you needed to register by 5 October 2026. Register now if you missed it; a late return is worse than a late registration.
  2. Find your UTR (10-digit Unique Taxpayer Reference) and Government Gateway login.
  3. Gather your P60 or final payslip, P11D if any, and interest and dividend totals.
  4. Total your side-hustle sales and allowable expenses for 6 April 2025 to 5 April 2026, or use the £1,000 trading allowance instead of expenses.
  5. Check whether you owe payments on account (due 31 January and 31 July).
  6. File online, note the amount due, and pay by 31 January.

A printable one-page version is free: Self Assessment checklist PDF.

Sources

Work out your own figure: the UK Side-Hustle Tax Tracker 2026/27, £4 on Payhip (or the free Lite version) calculates the extra tax and Class 4 NI on top of your PAYE salary.

Written with the help of an AI assistant and checked against GOV.UK on 22 Oct 2026. General information, not tax advice; if in doubt, contact HMRC or a qualified adviser.

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