Purpose - A synthetic indicator (SI) is developed to measure the sustainability of tourist destinations according to four proposed dimensions of sustainable development: social, economic, environmental and political. Its purpose is to determine the most appropriate indicators for each type of tourist destination, i.e. which variables should be considered in each territory according to its typology (environmental, social, economic and tourism). To test the usefulness and employability of the SI, it has been applied in the Algarve (Portugal). Three destinations were analysed in this region: Albufeira, Faro and Lagos, all three good examples of the well-known sun and beach tourismmodel. Design/methodology/approach - The SI is the result of a system of indicators. To reach the final result, a multi-criteria calculation has been used in which the most important variables that fit the territorial reality analysed have been included, based on an exhaustive analysis of more than 2,000 indicators proposed by various scientific studies and international organisations such as the United Nations World Tourism Organization. The results of this analysis have been weighted according to the opinion of the population. A survey of more than 1,800 questionnaires was carried out in tourist destinations with high seasonality and dependence on tourism in the Algarve, Portugal. Finally, the SI has been aligned with the Sustainable development goals (SDGs). Findings - The level of sustainability and the level of social concern regarding tourism activity were defined. In the Algarve, tourism is transforming the landscape and the local economy, and overcrowding is perceived as an economic activity that negatively affects sustainability. The concerns of the resident population about the impacts of tourism have served to identify priority strategies to improve the level of sustainability of the destinations. The three territories analysed present different problems and therefore require different strategies for action, mainly of a local public nature. The final result indicates the level of sustainability of the destination, which allows specific actions for improvement in the short, medium and long term to be generated. Practical implications - The results made it possible to develop lines of action aimed at improving the sustainable management of each tourist destination analysed. Involving the local population allows the residents of the destination to be part of tourism policies, assuming a bottom-up strategy. This research provides answers to destinations seeking to implement sustainable tourism, offering tourism sector managers tools for correct decision-making. Originality/value - This research presents a SI based on a system of indicators adjusted to the needs of the territory to be analysed, takes into account the opinion of the local population as a weighting factor and is in line with the 17 SDGs.