Answers · UK 2025/26
What happens if I don't file my Self Assessment tax return?
Missing the 31 January online Self Assessment deadline triggers an automatic £100 penalty, even if no tax is owed. After 3 months, daily £10 penalties start (up to £900). After 6 months, a further penalty of 5% of tax owed or £300 (whichever is higher). After 12 months, another 5%/£300 penalty applies.
Full answer
Missing the Self Assessment deadline carries escalating penalties. Understanding the schedule helps you act quickly to limit the damage. **SA filing deadlines (2026/27 return):** - **31 October 2027:** Paper return deadline - **31 January 2028:** Online return deadline AND payment of tax owed **Automatic penalty schedule for late filing:** | How late | Penalty | |---|---| | 1 day late (from 1 February) | **£100 automatic penalty** (even if no tax owed) | | 3 months late | **£10/day** (up to 90 days = max £900) | | 6 months late | **5% of tax owed or £300** (whichever is higher) | | 12 months late | **Further 5% of tax owed or £300** (whichever is higher) — and in serious cases HMRC can charge up to 100% of the tax owed | **Interest on late tax payments:** Separate from penalties, interest accrues on unpaid tax at the Bank of England base rate + 2.5% per annum from the due date. **Total worst-case scenario example (£2,000 tax owed, 13 months late):** - £100 (day 1) + £900 (days 91–180) + £100 (6 months penalty, 5% = £100 or £300, so £300) + £300 (12 months) = **£1,600 in penalties + interest** **Time to Pay arrangement:** If you cannot afford to pay, contact HMRC before the deadline to agree a **Time to Pay (TTP)** arrangement. Interest still applies, but penalties for late payment can be avoided. Apply via: Self Assessment payment helpline (0300 200 3822) or online via your Personal Tax Account. **Reasonable excuse:** HMRC accepts appeals against automatic £100 penalties if you have a "reasonable excuse" — serious illness, bereavement, computer failure on filing day, HMRC system outage. Excuses HMRC does not accept: "my accountant didn't do it in time" (unless you had the information to them early enough). **De-registering from SA:** If you no longer need to file (e.g. you are back in straightforward PAYE employment), contact HMRC to remove you from the SA register. Otherwise penalties continue indefinitely.
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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.