There is growing debate, both social and academic, about the possibility of levying an annual wealth tax. Until a few years ago, such a proposal appeared difficult to both implement and control, but recent technological innovations, which could greatly facilitate the periodic valuation of wealth, combined with improvements in international tax information sharing could make a “modern wealth tax” possible. Nonetheless, a number of challenges regarding its design still need to be addressed. In this paper, taking advantage of the Spanish experience – the only EU country to levy a wealth tax – we simulate the tax’s redistributive impact in the long run. This impact could well be substantial if all wealth were to be valued at market prices and compliance were high. Our results show that the family business exemption and the common income and wealth tax ceilings are highly regressive. We develop a tax simulator (SIMPA) that helps assess the effectiveness of alternative reforms with more comprehensive tax bases.