Achieving sustainability in today’s society requires the search for innovative tools that focus on using resources in such a way that they are not depleted. One such challenge is the climate and its impact on the whole way of life. In this regard, the article aims to offer a web-based application to support decision-making in determining the progress of the green transition. For this purpose, a software architecture of the web application is proposed, which maximally reflects the well-defined business logic. The underlying idea of the logic follows some EU Green Deal recommendations, which define which energy sources are considered renewable and which are not. That is why two main scenarios are proposed for calculating the energy consumption index from renewable sources and conventional sources. The applicability of the developed application is demonstrated based on data for the consumed energy from renewable and conventional energy sources forming the energy mix of Bulgaria for 2020 and 2023.