Form CT1
/fɔːm siː tiː wʌn/
Understand Form CT1, Ireland's corporation tax return filed with Revenue, including deadlines, required information, and tips to keep your company fully compliant.
Understand Form CT1, Ireland's corporation tax return filed with Revenue, including deadlines, required information, and tips to keep your company fully compliant.
Form CT1 is the annual corporation tax return that every Irish company must file with the Revenue Commissioners. It is the primary document through which your company reports its taxable profits, claims reliefs and allowances, and calculates the corporation tax due for each accounting period. Whether your company is trading profitably or recording a trading loss, the CT1 must still be filed.
For founders, the CT1 is one of the most important annual filings your company will make. It directly determines how much corporation tax your company owes and ensures your business remains in full tax compliance with Revenue. Filing accurately and on time protects your company from penalties, interest charges, and potential audit activity.
Every company registered in Ireland that is within the charge to corporation tax must file a Form CT1 for each accounting period. This includes active trading companies, dormant companies, and companies that have ceased trading but have not yet been formally dissolved. Your company registration number is used to identify your return within Revenue's systems.
Even if your company has no taxable income or has made a loss, you are still required to file. Failure to submit a CT1 is treated as a compliance failure, regardless of whether any tax is actually due. Revenue will issue a notice to file, and non-compliance can trigger enforcement action.
The CT1 is a detailed return covering all aspects of your company's financial activity during the accounting period. You must report trading income, investment income, rental income, chargeable gains, and any other sources of profit. Against these, you can claim deductions including trading expenses, capital allowances, and any trading losses carried forward from previous periods.
The form also requires details of any tax reliefs being claimed, such as the Research and Development Tax Credit, the Knowledge Development Box, or start-up relief for new companies. You must declare all related party transactions, details of any distributions made to shareholders, and confirm that the figures reconcile with your company's statutory accounts.
The return is submitted electronically through Revenue's Online Service (ROS). Your accountant will typically prepare the CT1 based on your company's financial statements, making accuracy in your underlying bookkeeping essential.
The Form CT1 must be filed within nine months of the end of your company's accounting period. For example, if your financial year ends on 31 December, your CT1 is due by 23 September of the following year when filing through ROS. The 23rd day of the month is the extended deadline for companies that both file and pay electronically.
Preliminary corporation tax must also be paid before the return is filed. Small companies, those with a tax liability under €200,000 in the prior year, pay preliminary tax in a single instalment by the 23rd of the sixth month after the start of the accounting period. Larger companies pay in two instalments. Getting these deadlines right is a core part of your company's tax compliance obligations.
Late filing of the CT1 carries serious consequences. Revenue imposes a surcharge on the amount of tax due. If the return is filed within two months of the deadline, the surcharge is 5% of the tax due, up to a maximum of €12,695. If the return is more than two months late, the surcharge increases to 10% of the tax due, up to a maximum of €63,485.
Interest on any unpaid tax also accrues from the original due date at a rate of approximately 0.0219% per day. Persistent late filing can result in Revenue restricting your company's tax clearance certificate, which may prevent you from tendering for public contracts or claiming certain grants. Late CT1 filing can also trigger the loss of your company's audit exemption, increasing your compliance costs when preparing abridged financial statements or full accounts.
The CT1 does not exist in isolation. It forms part of a broader network of tax filings that your company must manage. If you are a proprietary director, you will also need to file a personal Form 11 income tax return. Changes to your company's registered office require a Form B2 filing with the CRO, and your CT1 details must align with the information on your CRO annual return.
The figures in your CT1 should reconcile with your statutory accounts, though adjustments are made for items treated differently under tax law versus accounting standards. For example, accounting depreciation is replaced by capital allowances in the tax computation, and certain expenses allowable for accounting purposes may not be deductible for tax.
Start by ensuring your bookkeeping is accurate and up to date throughout the year. Clean financial records make the CT1 preparation process significantly smoother and reduce the risk of errors that could trigger a Revenue audit. Work with a qualified accountant who understands Irish corporation tax and can identify all available reliefs and deductions.
Set reminders for preliminary tax and filing deadlines well in advance. Build these dates into your compliance calendar alongside your CRO filing dates. Review your CT1 carefully before submission, checking that all income sources are declared, all reliefs are properly claimed, and the figures match your statutory accounts. A well prepared CT1 is one of the strongest signals of good financial governance in your company.
