Although the primary responsibility for safety is assigned to the operator of a nuclear installation, the regulatory body must ensure that the level of safety is adequate. The role of a regulator is to develop safety requirements, to monitor their implementation, and if necessary, to perform enforcement actions. This is done through the implementation of core and supporting functions; therefore, it is very important to monitor their effectiveness in a manner to proactively monitor nuclear safety. This work proposes a method using expert elicitation to develop a set of indicators to determine the effectiveness of the regulatory core functions (strategic indicators) that will compose a Regulatory Management Index (RMI). The supporting areas, which can have a direct impact on the core functions, were also considered as an indicator (cross-cutting indicators), but in contrast to the traditional indicator systems, they were not considered just as another indicator to be aggregated. The method introduces the use of a penalty factor on which a performance of a cross-cutting indicator below an acceptable range is used to penalize the related strategic indicator. Expert opinion is also used to weigh the relative importance between the indicators and to establish performance criteria for them. A case study was implemented to check the method’s feasibility.