This study presents the Multi-dimensional Flood Vulnerability Index (M-FLOVI), calculated by using an index-based method specifically tailored to capture the impact of nature-based solutions (NbSs) on vulnerability. It aggregates five vulnerability dimensions (physical, economic, environmental, social and institutional) into a single index within a multi-level framework. Each dimension is calculated from a set of indicators that can be computed with moderate data demands. These calculations generally require information about buildings, infrastructure, land cover, population, protected areas and cultural heritage, which can partly be obtained from open-access data. M-FLOVI ranges between 0 and 1, and it can be readily mapped and combined with flood hazard to produce flood risk maps. This paper elaborates a step-by-step M-FLOVI calculation in the Tamnava River Basin, Serbia, where various NbSs were proposed. Under the baseline conditions, most of the study area exhibits either moderate (83.5%) or low vulnerability (15.8%). These NbSs decrease future vulnerability in 6.6 km² (1.34%) of the study area. Afforestation (0.59%) and retention ponds (0.42%) decrease environmental vulnerability, while flood plain restoration (0.33%), which is expected to create a protected bird habitat, increases environmental vulnerability. These results suggest that M-FLOVI can effectively capture NbSs’ impacts on future vulnerability to floods.