In this Policy Brief, a conceptual framework is presented to conduct an ex-ante impact assessment for social innovation. The building blocks for an ex-ante impact assessment are goal formulation; developing the relationships between inputs, outputs and outcomes; determining the role of stakeholders to achieve the objectives; calculating the impact; and deciding on the social innovation. These building blocks are sequentially interconnected to each other. In the brief, we present the experience of three cases of social innovation with the framework. The following questions are discussed with results from the three case studies: How can you clarify your social goals and make them more measurable? How can you translate your goals into practical action roadmaps? How do you manage the sponsors and the stakeholders needed in your decision making? What kind of result can you expect from such an ex ante impact assessment? We summarize our lessons for each of these questions. In conclusion, our conceptual framework aims to be a practical guide to both assessor and assessee by structuring the development and decision process. A toolbox has been developed, which consists of a series of steps sprung from our conceptual framework.