The dates that matter
Your Company Tax Return (CT600) is normally due 12 months after the end of your accounting period.
Your Corporation Tax payment is usually due earlier — 9 months and one day after the period ends.
Your accounts are due at Companies House 9 months after the period ends.
In other words, the tax payment and the Companies House accounts fall due first, and the tax return itself can follow later — though it is simplest to complete everything in one sitting.
What late filing costs
Missing the HMRC tax return deadline triggers an immediate £100 penalty, a further £100 if the return is still outstanding after three months, and then percentage-based penalties on any unpaid tax after six and twelve months.
Filing accounts late at Companies House carries a separate penalty, starting at £150 and increasing the longer the delay.
Paying your tax late also accrues interest. Individually these amounts are modest, but they accumulate — and all of them are avoidable.
The simplest way to stay ahead
Because OneFiler prepares your accounts and tax return together and submits both, you can clear all your deadlines in a single sitting rather than tracking them separately.
Deadlines remain your responsibility, so we recommend filing well before the due date rather than on it.