Ireland operates a system of self-assessment where enterprises liable for Irish corporate income tax are assessed yearly on worldwide income by way of preliminary and annual tax returns. Tax payable in the year of assessment is based on the previous year's taxable income.
The number of preliminary payments depends on the previous year's tax liability of the enterprise. Enterprises with previous year's tax liability of greater than EUR 200,000 are required to make two preliminary payments, while those making less are required to make one. Final assessment for all enterprises is made with the annual tax return.
The taxpayer is responsible for calculating the tax liability and submitting payment. If a taxpayer fails to file a return, or the return is incorrect or incomplete, an estimated assessment may be issued by the tax authorities. Such assessment cannot be appealed until the taxpayer files a proper return.