The Temporary Solidarity Tax on Great Fortunes came into force in Spain at the end of 2022. This tax managed at state level and complementary to the Wealth Tax, will seek to harmonise the taxation of wealth in all the autonomous communities under the common regime. In this paper the taxation of wealth in Spain is analysed, as well as the reform proposals put forward to date. The new state tax is estimated using microsimulation techniques for the year 2022, with the aim of obtaining the main revenue effects that its implementation will have. Its impact will be unequal between autonomous communities due to the existing differences in the regional regulations of the Wealth Tax.