Sources checked 10 November 2026
Put the CT1 date in your diary
For mandatory electronic filing through ROS, the CT1 and the balance of corporation tax are generally due by the 23rd day of the ninth month after the end of the accounting period. For a 31 December period end, that generally means 23 September of the following year.
Check preliminary tax separately
Preliminary corporation tax can fall due before year end. The rules differ for small and large companies, and there are separate rules for qualifying first accounting periods. Check the Revenue guidance before relying on a prior year’s payment schedule.
Get the year-end records ready
Close the bookkeeping, reconcile bank and control accounts, and collect loan statements, asset invoices and any director balance details. Tell your accountant about prior payments or credits that may affect the balance.
Official guidance
- Revenue guidance on CT payment and filing
- Revenue guidance on preliminary CT deadlines
- Revenue preliminary CT rules
This guide covers general rules. Check the dates and requirements that apply to your company or tax return.