BACKGROUND: People with intellectual and developmental disabilities (IDD) experience work ability decline through aging and disability (WADAD), conceptualized as the process of deterioration in work ability resulting from the interaction between disability and aging, which has a direct impact on their job. OBJECTIVE: There is a need to focus on how this decline can be detected and to identify the main areas and indicators of WADAD in people with IDD, in order to build a targeted prototype assessment tool to determine a prevention protocol that extends people’s positive working lives for as long as possible. METHODS: Literature review, Delphi panel, and working group through Modular Object-Oriented Dynamic Learning Environment (MOODLE). RESULTS: Creation of a tool, composed of 76 items, 6 dimensions, and 17 indicators, to assess WADAD in people with IDD.