Answers · UK 2025/26
When is the Self Assessment deadline for 2025/26?
The 2025/26 Self Assessment return covers income from 6 April 2025 to 5 April 2026. Paper returns are due by 31 October 2026; online returns and any tax owed by 31 January 2027. Missing it triggers an automatic £100 penalty even if no tax is owed.
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Self Assessment deadlines for the 2025/26 tax year: register for SA by 5 October 2026 if newly self-employed; file a paper return by 31 October 2026; file online and pay any balancing payment plus first payment on account by 31 January 2027; second payment on account by 31 July 2027. Penalties: £100 fixed for being one day late, even with no tax due; £10/day after 3 months (up to £900); 5% of unpaid tax (or £300 if greater) at 6 months and again at 12 months. Interest on late paid tax is currently 8.25% (Bank Rate + 2.5%). Avoid penalties by filing early through your Government Gateway account at gov.uk/log-in-file-self-assessment-tax-return or by using compatible third-party software (mandatory for MTD ITSA from April 2026 for self-employed/landlord income above £50,000).
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This answer is informational only and does not constitute financial, tax or legal advice. Figures are for the 2025/26 UK tax year. See our methodology and sources.