UK Tax Deadline Checker — Am I Late?

Online Self-Assessment returns and any balancing payment are due by 31 January following the end of the tax year. Paper returns must reach HMRC by the earlier 31 October deadline. Missing the deadline triggers an automatic £100 fixed penalty, plus daily and percentage penalties as time passes.

Late VAT returns add a point to your VAT points record; a £200 penalty applies when the relevant threshold is reached. For late payments due from April 2026, the first penalty is 3% at day 15 and another 3% at day 30, followed by a second penalty accruing at 10% a year from day 31. Late-payment interest is separate.

Your CT600 must be filed within 12 months of the end of the accounting period. Corporation Tax is normally due earlier — 9 months and 1 day after period end. For filing dates from 1 April 2026, the fixed late-filing penalty is £200, with another £200 after three months; tax-related penalties can follow at later milestones.

P11D forms and the associated P11D(b) must be filed by 6 July following the tax year. Class 1A NI is payable by 22 July (19 July by post). The calculator's £100 per 50 employees per month estimate is specifically the late P11D(b) employer-return penalty; individual P11D failures can be treated differently.

Failing to file a Confirmation Statement is a criminal offence: the company and its officers may be fined, and Companies House can start strike-off proceedings. The calculator does not estimate the court fine; it flags the compliance risk from the first overdue day.