Compliance · 2026/27 tax year
Self Assessment late filing penalty estimator UK 2026/27
Rough estimate of HMRC late-filing penalties for missing the online Self Assessment deadline, based on days late and tax due. Interest on late payment is excluded.
Fixed late filing: £100
Daily penalties (model): £300
Six-month (model): £0
Twelve-month (model): £0
Total (rough): £400
Illustrative only. Interest on late tax, payment surcharges, and reasonable-excuse appeals are not included.
Understanding your results
Reasonable excuse appeals exist because life is not linear — HMRC’s manuals describe evidence types; keep GP letters or supplier outage screenshots with your appeal pack.
Daily penalties stop after ninety days at the three-month stage in many cases, but the headline still hurts — treat the online filing date like a client deadline with reputation risk.
Partnership returns and trusts carry different penalty matrices; this estimator targets individual Self Assessment lateness only.
Interest on late paid tax runs separately; even if you file on time, missing the payment deadline generates its own charge.
If you cannot pay, still file — penalties for late payment are not identical to late filing, and payment plans exist.
Disclaimer: This is a guidance estimate based on the 2026/27 tax year. It is not personal tax advice — consult an accountant or HMRC for your specific circumstances.
About this calculator
HMRC charges an automatic £100 if you file even one day late (unless you have a reasonable excuse). Longer delays add daily penalties and further fixed penalties linked to tax due.
Our model is intentionally conservative and rounded — real penalty notices depend on your exact behaviour, reasonable excuse appeals, and partnership returns.
Late payment penalties and interest are different from late filing. Budget for both if you miss January.