Answers · UK 2025/26
What happens if I miss the self-assessment deadline?
Missing the 31 January deadline triggers an automatic £100 penalty, with further penalties at 3, 6 and 12 months, plus daily £10 penalties from 3 months late.
Full answer
If you miss the 31 January online self-assessment deadline: automatic £100 fixed penalty (even if no tax is owed or if you get a refund); after 3 months, daily penalties of £10/day (up to 90 days = £900 max); after 6 months, additional 5% of tax due or £300 (whichever is greater); after 12 months, a further 5% or £300. Late payment interest accrues on unpaid tax from 1 February. Reasonable excuse (serious illness, bereavement) can be used to appeal penalties.
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.