<p>Floods are among the most destructive natural disasters, necessitating effective tools to assess and enhance the capacity to manage them. This study introduces the Flood Damage Mitigation Index (FDMI), a novel metric designed to quantify municipal-level flood management capacity using parameters from a logistic growth model. The FDMI integrates two parameters: <i>a</i>, which represents the sensitivity of flood damage to increasing rainfall, and <i>b</i>, which represents the rainfall threshold at which significant damage occurs. Smaller <i>a</i> values indicate lower damage sensitivity, whereas larger <i>b</i> values suggest greater mitigation capacity by delaying the onset of damage. Together, these parameters provide a comprehensive assessment of flood mitigation capacity. Using the maximum daily rainfall as the independent variable and flood damage costs as the dependent variable, logistic growth functions were applied to 228 municipalities across South Korea. The FDMI revealed significant regional variability, with metropolitan areas exhibiting higher values owing to well-developed infrastructures and advanced flood defenses. Correlation analysis showed that policies such as increasing rainwater pump capacity, river improvement rates, and retention basin areas were significantly and positively associated with <i>b</i>, indicating their effectiveness in increasing damage thresholds. The FDMI offers a practical tool for policymakers to identify regions that require targeted interventions and prioritize investments in flood mitigation infrastructures. By providing a quantitative basis for decision-making, the FDMI contributes to region-specific strategies and supports broader climate-adaptation policies. Case studies further showed that parameter adjustments through flood mitigation policy interventions can effectively reflect enhancement of flood management capacity.</p>