If the taxpayer notices errors or omissions in the details declared once the Income Tax draft or return has been filed, the procedure for modifying the anomalies is different depending on whether the errors or omissions are to the detriment of the taxpayer or the Public Treasury.
* Errors to the detriment of the taxpayer:
If the taxpayer has unduly declared some exempt income, calculated sums for higher amounts than due or forgotten to make a reduction or deduction to which he/she was entitled, in Renta WEB 2016 there is a specific new section where he/she may ask to correct their self-settlement, although they may also continue to request self-assessment rectifications in writing at the Tax Agency Branch or Office corresponding to his/her tax address, provided the Administration has not made a provisional or final settlement for this reason and that a period of four years (counted from the day after the end of the period for presenting tax returns or, if the tax return was presented late, from the day after presentation) has not elapsed.
* Errors to the detriment of the Public Treasury:
Errors or omissions in tax returns already presented that have led to a payment of less than the sum that should have been legally due or to a higher refund than should have been due must be corrected through the presentation on Renta WEB of a supplementary tax return to the one originally filed.