Overview
- Missing the 31 January cut-off triggers an automatic £100 late-filing penalty even if no tax is due or the bill is paid on time.
- Interest on unpaid tax is reported at 7.75%, with further surcharges and escalating penalties added at three, six and twelve months.
- HMRC’s helpline closes 6pm Friday 30 January and reopens Monday 2 February, with webchat available 8am–4pm on Saturday 31 January.
- Last year about 600,000 late filers faced £325 million in fines and interest, and self-assessment tax debts were cited at £8.7 billion.
- From 6 April 2026, Making Tax Digital will require sole traders and landlords earning over £50,000 to use compatible software, with a points-based penalty regime piloting ahead of wider rollout.