Under the self-assessment system of tax administration, responsibility for the submission of a correct tax return rests with the taxpayer. Revenue inputs the data on the tax returns into its computer systems, issues a notice of assessment to taxpayers and creates a tax charge or repays any tax overpaid, as appropriate.
Under the self-assessment system the majority of income tax payers file their tax returns with Revenue each year around 31 January – the return filing deadline. Inevitably, in this situation errors will arise in the processing of such a large volume of information. Revenue staff do, however, perform a routine level of checking or "repair" of tax returns before inputting the data into the computer systems, so as to try to eliminate some of the more common errors made by taxpayers or their agents. This procedure at the initial processing stage ensures many errors or omissions that would otherwise give rise to incorrect assessments are remedied, thus increasing the overall level of accurate tax assessments.