Preventing the increase of economic inequality in a non-growing economy is a major challenge. In post-growth research, scholars agree that reducing the income and assets of the wealthy must be part of any strategy for reducing inequality. Nevertheless, caps on wealth and income remain surprisingly under-researched. After discussing the role of these caps in post-growth transformation, this paper aims to fill this gap by exploring the main parameters that policymakers need to consider when designing caps on income or assets. We performed a qualitative content analysis of 14 policy proposals, including four historical cases. We then built an analytical framework with seven key parameters. This framework reveals a broad set of public policies that policymakers and researchers can consider, including new options for wealth caps. We furthermore discuss how such policies should be designed to increase public support, and we highlight recurring patterns about the context in which they were proposed. We also show how these radical solutions reduced economic inequality in the 20th century in western countries and how policymakers can draw on those examples to design post-growth policies that decrease inequality and are also popular.