The CT1 corporation tax return
The CT1 is the company’s corporation tax return to Revenue. Returns filed and paid through ROS are due by the 23rd day of the ninth month after the end of the accounting period. Any balance of tax still owed is paid on the same date.
| Year-end | CT1 and balance due (ROS) |
|---|---|
| 31 December 2025 | 23 September 2026 |
| 31 March 2026 | 23 December 2026 |
| 30 June 2026 | 23 March 2027 |
| 30 September 2026 | 23 June 2027 |
Late filing brings a surcharge on the tax due and can restrict certain reliefs, so it is worth treating the date as fixed.
Preliminary tax
Most companies also pay preliminary tax before the year has ended. A small company, broadly one whose corporation tax for the previous year was €200,000 or less, usually pays in one instalment by the 23rd of the eleventh month of the accounting period. Larger companies pay in two instalments, in the sixth and eleventh months. A newly trading company with a small first-year liability may not need to pay preliminary tax at all in its first period.
The CRO B1 annual return
Every Irish company, including dormant and non-trading companies, files a B1 annual return with the Companies Registration Office. It is due within 56 days of the Annual Return Date. Most companies attach financial statements, and those must be signed and made up to a date no more than nine months before the Annual Return Date.
Because the Annual Return Date and the financial year-end are different dates, many directors only discover the B1 when a late filing penalty arrives. Missing it can also cost the company its audit exemption for two years.
The other recurring dates
- VAT returns, usually every two months, by the 23rd of the following month through ROS.
- Payroll submissions to Revenue each time employees are paid, with the monthly liability due by the 23rd.
- The director’s Form 11, normally due by 31 October, with an extended date for ROS filers each November.
- Updates to the Register of Beneficial Ownership when owners change.
Frequently Asked Questions
When is the CT1 due in Ireland?
For ROS filers, by the 23rd of the ninth month after the accounting period ends. A 31 December year-end gives 23 September.
Is the B1 due on the same date as the CT1?
No. The B1 is due within 56 days of the Annual Return Date set by the CRO, which is separate from the financial year-end.
Do dormant companies have to file?
Yes. Dormant companies still file the B1 and generally a CT1 unless Revenue has agreed otherwise.
Sources (3)Checked 26 October 2026
This guide is general information, not advice for your situation. Rules change, so check the official sources or talk to us before acting on it.