We define and evaluate a framework for estimating the energy consumption of pervasive Java-based software systems. The framework’s primary objective is to enable an engineer to make informed decisions when adapting a system’s architecture, such that the energy consumption on hardware devices with a finite battery life is reduced, and the lifetime of the system’s key software services increases. Our framework explicitly takes a component-based perspective, which renders it well suited for a large class of today’s distributed, embedded, and pervasive applications. The framework provides a novel approach that facilitates the accurate estimation of a system’s energy consumption both during system construction-time and during runtime. In a large number of distributed application scenarios, the framework showed very good precision on the whole, giving results that were within 5% of the actually measured power losses incurred by executing the software.