How to modify a tax return already filed

If the period to be rectified is prior to 2024

In the event of an error in the declaration, there are several possibilities depending on the type of error:

If you haveoverpaid or you have declared a lower amount to be refunded for the Corporate Tax (favorable situation for the taxpayer), you can request a correction of the self-assessment filed before four years have elapsed since the deadline for filing the aforementioned self-assessment.

If you have underpaid or declared a larger amount due for Corporate Tax (an unfavorable situation for the taxpayer), you must file a supplementary self-assessment, checking the "supplementary self-assessment" box on Form 200, indicating the receipt number from the previous self-assessment, and completing the "Deductible (only in the case of a supplementary declaration)" box with the amount resulting from the previous self-assessment.

If the error relates to an information box or the account number for which the refund is being requested, or another error that does not affect the result of the assessment, you must submit a request to rectify the self-assessment within four years of the deadline for filing the aforementioned self-assessment.