Mangrove ecosystems provide essential social-ecological functions that support millions of people worldwide. Yet rapid mangrove loss is eroding their capacity to deliver these functions, threatening both ecosystem stability and human well-being. In this study we mapped areas of high risk of functional loss by introducing the concept of functional insurance, defined as the degree to which functions are supported by multiple and abundant species. We built a global database linking 101 mangrove taxa to 52 ecological and social-ecological functions using a two-round Delphi-based expert survey and combined it with expert-based coverage estimates in 43 countries and overseas territories to calculate functional area, a spatial measure of functional insurance. We overlaid this functional area with mangrove loss data (2015–2020) and analysed it using piecewise structural equation models. Our results show that Small Island Developing States and some countries in West Africa and Central America face high risk of functional loss, often combining low functional area indicating high functional vulnerability with high recent mangrove loss. Agricultural land cover near mangroves and recent mangrove cover loss were key predictors of variation in functional area across countries and territories. Our findings underscore the need to prioritise functionally vulnerable regions in conservation and planning efforts. This framework offers a scalable tool to assess and map the degree to which key mangrove functions are supported by multiple and abundant species, helping sustain the livelihoods they underpin.