The integration of schedulability analysis with the industry standard Unified Modeling Language (UML) allows real-time developers to detect, at an early stage of development, unfeasible (unschedulable) real-time architectures. It thus prevents costly design mistakes and accelerates development schedules. This integration, accomplished through the timing extensions of UML, also allows the developer to verify the real-time performance of the design throughout the software lifecycle. In this paper, we provide an overview of UML with its real-time extensions and the Rate Monotonic Analysis. Mainly, we show how to perform schedulability analysis of a UML model and we also discuss the implications of having timing analysis applied to UML designs.