In general

Any errors or omissions in declarations already submitted that have resulted in a lower payment than legally required or a higher refund than appropriate must be corrected by submitting a supplementary self-assessment to the one originally submitted.

Any situations or circumstances that arise which result in the loss of the right to a reduction or exemption already applied in a previous declaration must also be regularised by submitting supplementary self-assessments.

However, the loss of the right to certain deductions, as discussed in this same Chapter under the heading " Increase in net contributions , state and regional, due to loss of the right to deductions from previous years", must be regularized in the self-assessment of the year in which non-compliance with any of the requirements for consolidating the right to said deductions occurred.

In accordance with the provisions of article 122.2 of Law 58/2003, of December 17, General Tax Law ( BOE of the 18th), a supplementary self-assessment may also be submitted to request a refund lower than that self-assessed in the original declaration, in the event that the refund has not been made by the tax administration.

Supplementary self-assessments, which may give rise to an amount to be paid or an amount to be refunded that is lower than that previously self-assessed in the event that the requested refund has not yet been made by the tax authorities, must be made on the forms corresponding to the year that is the subject of regularisation.