The key difference between the two concepts is that settlement, either temporary or permanent, is practiced by the tax authorities and, as such, constitutes an administrative act. By contrast, the self -assessment, also denominated settlement-declaration is practiced by the taxpayer themselves. Although it is an act of application and calculation of tax, it is not an administrative act.
In short, the self - assessment involves not only a statement made by the taxpayer, but also the calculation and payment of tax is derived thereof.
However, it should be noted that the fact that the Administration accepts income from self-assessments of taxpayers, it does not make such acceptance in settlements; provisional or otherwise, but is a mere activity fund.
Almost all state taxes are managed on the reverse charge procedure, having transferred our tax system it is the taxpayer's obligation to calculate (self - assess) the debt that corresponds. In this sense, the only peculiarity lies in the inheritance tax, where the reverse charge procedure is not mandatory, but optional.