🏢

Corporation Tax

Corporation Tax Return (CT1)

CT1 filing dates, preliminary tax, and how to calculate your liability

📅 Key Dates

6 months before year end Corporation Tax Preliminary (large companies)
31 days before year end CT Preliminary (small companies)
9 months + 23 days after year end CT1 return and balance due via ROS

📋 Overview

Every company must file a Corporation Tax return (CT1) within 9 months and 23 days of the end of its accounting year. For companies with a December 31 year end, this means a CT1 deadline of 23 September. Corporation Tax is charged at 12.5% on trading income.

✅ How to File — Step by Step

  1. File the CT1 return via ROS.
  2. Compute trading profits, deduct allowable expenses and capital allowances.
  3. Calculate CT at 12.5% on trading income (25% on passive/non-trading income).
  4. Pay any balance of CT due (after preliminary payment) with the return.
  5. Include Form 46G for connected party transactions (if applicable).

⚠️ Penalty if Missed

10% surcharge on CT liability for late filing. Interest at 0.0219% per day on unpaid balance. Persistent non-filing can result in Revenue estimated assessments.

📄 Revenue Forms

❓ Frequently Asked Questions

Reviewed by Vitor Alves

Founder, d'Emilia Accounting — specialising in tax compliance for immigrants and self-employed in Ireland.

Talk to us →