Self Assessment deadlines and penalties 2025/26
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In short. For 2025/26 income, paper returns are due 31 October 2026 and online returns 31 January 2027 — also the payment deadline. HMRC charge an automatic £100 penalty for missing the filing deadline (even with nothing owed), then £10/day after 3 months (up to £900), 5% of tax owed at 6 months, and another 5% at 12 months. Late-paid tax also attracts interest, set at Bank Rate + 4 percentage points from April 2025.
Self Assessment penalties are calculated automatically and there is no minimum tolerance for being a day late. The interest rate on overdue tax has been deliberately raised since 2024 and is reviewed each time Bank Rate changes.
Quick answer: Self Assessment deadline →
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Key dates for the 2025/26 tax year
- 6 April 2026 — 2025/26 tax year ends; 2026/27 starts
- 5 October 2026 — deadline to register for Self Assessment if filing for the first time
- 31 October 2026 — paper Self Assessment return deadline (midnight)
- 30 December 2026 — deadline to file online and ask HMRC to collect tax under £3,000 through your PAYE tax code
- 31 January 2027 — online Self Assessment deadline and balancing-payment deadline; also the first payment on account for 2026/27
- 31 July 2027 — second payment on account for 2026/27
Late-filing penalties
- 1 day late — £100 fixed penalty, even if no tax is owed
- 3 months late — daily penalties of £10 per day for up to 90 days (maximum £900)
- 6 months late — additional 5% of the tax owed, or £300 if greater
- 12 months late — additional 5%, or £300 if greater (more in deliberate cases)
Late-payment penalties and interest
Tax paid late attracts both interest and a separate penalty. The penalty is 5% of the unpaid tax after 30 days, another 5% at 6 months and another 5% at 12 months.
Interest is charged on unpaid tax at Bank Rate plus 4 percentage points (raised from Bank Rate + 2.5 pp from 6 April 2025). With Bank Rate at 4.25% in May 2026, HMRC's late-payment interest rate is 8.25%. Interest on overpaid tax is set at Bank Rate minus 1 percentage point with a 0.5% floor.
FAQ
- Can I appeal a £100 late-filing penalty?
- Yes, by submitting a formal appeal within 30 days of the penalty notice and showing a 'reasonable excuse' (serious illness, bereavement, postal failure, HMRC system failure). Forgetting or being too busy is not accepted.
- What happens if I file the return on time but pay the tax late?
- No filing penalty applies, but a 5% late-payment penalty is charged once tax is 30 days overdue, with further 5% charges at 6 and 12 months, plus daily interest at Bank Rate + 4 pp.
- Can I pay HMRC in instalments?
- HMRC's online 'Time to Pay' service can spread Self Assessment debt up to £30,000 over 12 months, provided returns are up to date and the request is made within 60 days of the payment deadline.