Information on complementary self-assessments

  • What is a supplementary self-assessed tax return?

    Additional self-assessments are those that relate to the same tax obligation and period as others that have previously been filed, and which result in a greater amount to be paid, or a quantity to return or compensate that is less than the amount resulting from the previous self-assessment, which will subsist for the unaffected party.

    When can a supplementary self-assessment be filed?

    You can only file an additional self-assessment to:

    • Request the reimbursement or compensation of a lesser quantity.
    • Make a payment for a greater amount.

    Therefore, if a tax obligor considers that a self-assessment has harmed their legitimate interests, they will only be able to obtain the compensation of the harm suffered by commencing a self-assessment rectification procedure.


    Both Section 122 of the General Taxation Act nº 58/2003 and Section 118 of the General Regulations on Application of Taxes, passed by Royal Decree 1065/2007, establish that self-assessments can only be supplementary (can never be substitutive), that is, they always result in an amount favourable to the Administration, unlike what occurs with tax returns (for example, informative tax returns) which can be supplementary or substitutive, since they are not associated with a deposit or refund.

    Characteristics of supplementary tax returns

    1. There must always be a self-assessment submitted prior to the one it complements.The amount of the initial self-assessment will be deducted from the tax liability resulting from the supplementary self-assessment.
    2. If a supplementary self-assessment is filed in relation with an obligation and period for which an inadmissible refund has already been obtained, in whole or in part, the unduly obtained amount must be deposited plus any liability which may result from the supplementary self-assessment.
    3. In the submission, the taxpayer must state that it is a supplementary self-assessment, plus the tax obligation and the period in question.All the data, both new or modified, and those included in the initial tax return must be recorded.

    Submission periods

    They can be submitted during the established timeframe for their filing, or after this period, provided that the timeframe for the Administration to determine the tax debt has not elapsed.In this latter case they are considered extemporaneous, and if they result in an amount to be deposited, the surcharges provided for in Section 27 of the LGT will be applied, if there has been no previous requirement for filing.

    Filing of supplementary self-assessments

    A supplementary self-assessment is filed when the error has been to the detriment of the Public Treasury.The situation must be regularised by means of the submission of the corresponding form (the one originally submitted) of the tax year in which the error occurred marking the "supplementary" box.