Sustainable urban transformation practices play a critical role in implementing the economic, environmental, and social dimensions of sustainable development in cities. Sustainability indices are important parameters for achieving sustainable development goals. The use of these indices supports the making of strategic decisions for the future of cities, such as in urban transformation practices. Indicators and data are defined as vital tools for evaluating the success of sustainability policies and monitoring the economic, environmental, and social performance of cities. Establishing more comprehensive and accessible data collection systems at the local level and effectively sharing this data is crucial for developing policies based on these indices. This study highlights the significance of sustainable urban transformation practices within the framework of the Sustainable Development Goals (SDGs), emphasizing the methodologies and challenges encountered during the development of a Sustainability Index tailored to the Bağcılar district in Istanbul. The findings indicate that localized data collection and indicator adaptation are essential for achieving measurable and actionable sustainability targets, despite significant limitations in data accessibility. Bağcılar offers an important area of study in terms of sustainability with its dynamics such as rapid population growth, dense construction and socio-economic differences. Planning urban transformation projects within the framework of sustainability principles is a strategic necessity for Istanbul and similar metropolitan cities. By establishing a system that tracks regular, reliable, and internationally standardized data, it will be possible to create measurable, reportable, and comparable targets for sustainable urban transformation practices. However, in developing countries like Turkey, deficiencies in data collection and analysis processes make it difficult to achieve sustainability goals. This study suggests that improving data collection processes and increasing transparency are fundamental steps to ensuring sustainable urban transformation.