To address the learning crisis and other challenges facing children and youth (those 15-24 years of age) it is critical for governments, multilateral and bilateral funders, other donors, and implementers to have a clear understanding of program costs and cost breakdowns to inform financing decisions. For nearly a decade, the Center for Universal Education (CUE) at the Brookings Institution has led the Childhood Cost Data initiative, a research project focused on the collection, analysis, and use of cost data to increase the volume and quality of funding for programs targeting children and youth. The initiative's end goal is to improve learning and life outcomes for the youngest generation through these advancements. As part of this initiative, Brookings developed the Childhood Cost Calculator (C3), intended to facilitate cost analysis. This study introduces C3, the tool's various dimensions and functionalities, and presents learnings from three case studies from piloting the calculator in the education or early childhood development (ECD) sectors in Cambodia, Ghana, and Honduras. It concludes with suggestions for a way forward that supports funders, implementers, and researchers to better use cost data to make strides in tackling the multiple crises facing children and youth today.