A company's CT1 return and tax payment are due 9 months after the end of its accounting period. Preliminary tax must be paid during the year.
| Accounting period end | CT1 filing + payment deadline |
|---|---|
| 31 March 2025 | 31 December 2025 |
| 30 April 2025 | 31 January 2026 |
| 31 May 2025 | 28 February 2026 |
| 30 June 2025 | 31 March 2026 |
| 31 July 2025 | 30 April 2026 |
| 31 August 2025 | 31 May 2026 |
| 30 September 2025 | 30 June 2026 |
| 31 October 2025 | 31 July 2026 |
| 30 November 2025 | 31 August 2026 |
| 31 December 2025 | 30 September 2026 |
| 31 January 2026 | 31 October 2026 |
| 28 February 2026 | 30 November 2026 |
| 31 March 2026 | 31 December 2026 |
Companies must pay preliminary CT during the accounting period itself — before the return is filed. The rules differ by company size:
| Company type | First instalment | Second instalment | Amount |
|---|---|---|---|
| Small company (CT < €200k in prior year) | — | Day 21 of month 11 | 90% of current year liability OR 100% of prior year |
| Large company (CT ≥ €200k in prior year) | Day 21 of month 6 | Day 21 of month 11 | 45% then 55% of final liability |
Example: small company with 31 December 2026 year-end — preliminary CT due by 21 November 2026.
D’Emilia Accounting files Form 11, CT1, and VAT returns for individuals and businesses in Ireland. Never worry about a late filing surcharge again.
A company's CT1 return and final tax payment are due 9 months after the end of its accounting period. For a 31 December 2025 year-end, the deadline is 30 September 2026. For a 31 March 2026 year-end, it is 31 December 2026.
Companies must pay preliminary tax (an advance payment) during the accounting period. Small companies (CT liability below €200,000) pay one instalment: 90% of final liability by the 21st day of the 11th month of the period. Large companies pay two instalments — in month 6 and month 11.
A company whose CT liability for the previous year exceeded €200,000. Large companies must pay their first preliminary tax instalment by the 21st of the 6th month of the accounting period, and their second instalment by the 21st of the 11th month.
The same late filing surcharge applies as for income tax: 10% of the CT liability if filed up to 2 months late, rising to 20% if filed more than 2 months late, capped at €63,493. Daily interest of 0.0219% also applies to any unpaid tax from the due date.
Revenue does not routinely grant CT1 extensions. Companies that file via ROS may receive a minor extension (typically a few days) — check the ROS system for the exact date. Unlike income tax, there is no standard two-week ROS extension for CT1.
20% of the corporation tax liability for the period, capped at €63,493. On a CT liability of €50,000, the surcharge would be €10,000. On a liability of €400,000, the surcharge is capped at €63,493 rather than €80,000.
Disclaimer: General information only. Verify dates at revenue.ie. Not tax advice.
Our accountants handle your filings, send you deadline reminders, and ensure you are always compliant with Revenue — for income tax, corporation tax, VAT, PAYE and more.