Self-Assessment late-filing penalty

Map late-filing penalty trigger dates for a Self-Assessment tax return: £100 immediate, £10/day after 3 months, 5% / £300 at 6 months, another at 12 months.

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All values calculated using standing rule (TMA 1970 Schedule 55) figures.

Used to estimate which penalty bands you fall into.

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How this is calculated

Late-filing penalties for Self-Assessment are set by Schedule 55 of the Taxes Management Act 1970:

  • Day 1 after deadline: immediate fixed £100 penalty (even if you owe no tax).
  • 3 months late: daily £10 penalties for up to 90 days (max £900).
  • 6 months late: additional £300 or 5% of the tax due, whichever is greater.
  • 12 months late: another £300 or 5% (or up to 100% of the tax in cases of deliberate withholding).

HMRC adds late-payment interest on top of any tax due, charged daily. You can appeal a penalty if you have a "reasonable excuse" — but ignorance of the deadline is not accepted.

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