The availability of many microplastic analysis methods is challenging for researchers and policy makers when tasked with choosing optimal methods for their research question and a given budget. In this study, a cost-effectiveness analysis of methods for microplastic analysis in seawater was performed using survey data acquired from experts. Total analysis cost per method was determined accounting for labour and equipment costs, while method effectiveness was scored based on their ability to confirm the plastic nature of particles, their minimum detectable particle size, and other parameters. Results were validated and discussed during two workshops with scientists and policy makers. The resulting predictive tools allow to identify the most cost-effective methods for specific scenarios, and their associated cost. They mark an important step towards a more effective and informed approach to monitoring and managing microplastic pollution in the marine environment, ultimately contributing to the protection of marine ecosystems and human health.