Adequate measurement, assessment, and regulation of financial development stability are key components, the formation of effective macroprudential policies, and the coordination of these policies among countries. However, an analysis materials on the subject shows that work in this area is fragmented,. In this regard, the purpose of this study is to develop a methodology for diagnosing and regulating the stability of financial development based on a systematic approach. The study used systematic, comparative, and GEO analysis, econometric methods. As a result, new indicators have been developed to diagnose the financial development of countries. The authors also propose criteria, which could be used to signal the need for countercyclical regulation tools. The novelty of the study lies in a systematic approach to the diagnosis and regulation of the stability of financial development. The systemic nature of the study is ensured by the application of the statistical framework of the System of National Accounts. Testing of the developed indicators and criteria was carried out in relation to the OECD+ (Organisation for Economic Co-operation and Development) countries for the period 2007–2020. As a result of the testing, a rating of countries was built according to the level of stability of financial development. This rating highlighted leading countries as well as countries generating systemic risks. The study also assessed the legal grounds behind the introduction of a countercyclical markup by a number of countries. The new diagnostic and regulatory system has a number of advantage—it is highly representative and objective by nature, and has a wide range of applications. The use of this system will improve the complexity and quality of diagnosing and regulating the stability of financial development at the national and global levels, as well as increase the effectiveness of public decision-making.