Ireland Corporation Tax — CT1 Return

Confirm the company is Irish-resident (incorporated in Ireland or centrally managed and controlled here), establish the accounting period end date (maximum 12 months), retrieve the CRO number and Revenue CT reference, and check whether the company is a close company under s430 TCA 1997. This phase also determines whether a preliminary tax payment under s958 TCA 1997 was made on time (large company: 31st of month 6; small company: 31st of month 11 of the accounting period).

Prepare the adjusted trading profit or loss under Schedule D Case I (TCA 1997 s21), applying the 12.5% trading rate. Identify any passive income streams — rents, interest, royalties, foreign dividends — subject to the 25% rate under s21A. Reconcile management accounts or trial balance to the CT1 income panels, stripping non-deductible items (entertainment per s840, client gifts, depreciation replaced by capital allowances) and adding back disallowable provisions.

Compute capital allowances on plant and machinery at 12.5% straight-line over 8 years (TCA 1997 Part 9), motor vehicles capped at EUR 24,000, and industrial buildings at 4% over 25 years. Identify any Accelerated Capital Allowance (ACA) claims for energy-efficient equipment listed by the SEAI. Review disposals for balancing charges or allowances.

Review whether the company has qualifying R&D expenditure under s766 TCA 1997. The R&D tax credit is 30% of incremental qualifying expenditure (Finance Act 2024 increased the rate from 25% to 30%). Separately check eligibility for the Knowledge Development Box (KDB) at the 6.25% effective rate on qualifying IP income, and any Section 481 film relief or other sectoral credits. Assess loss relief options — current year set-off, carry-back against prior period, or carry-forward.

Assemble the full corporation tax computation: Case I income at 12.5%, passive income at 25%, chargeable gains at 33% (grossed up via s78 TCA 1997), less capital allowances, losses, and credits. If the company is a close company with undistributed investment or estate income, apply the 20% surcharge under s440 TCA 1997. Compute the final CT liability net of preliminary tax paid.

Irish companies with turnover above EUR 250,000 (or forming part of a group) must submit iXBRL-tagged financial statements with their CT1 via ROS. Prepare or validate the iXBRL file, attach it to the CT1, and submit through ROS by the filing deadline (9 months after accounting period end; pay & file date is the same). Confirm submission receipt number and balance tax payment.