This collaboration between GridLab and Telos Energy aims to fill a crucial gap in utility planning methods to allow data center flexibility to be considered up front in resource planning. NV Energy of Nevada was used as a case study due to its rising data center load growth, with the intent to create a replicable method for other regions. This report evaluates the resource adequacy benefits of data center flexibility, including avoided capacity needs and costs. It validates a framework for incorporating large load flexibility into resource planning by allowing it to count towards a planning reserve margin (PRM) requirement via a demand-side effective load carrying capability (ELCC). The results of this case study highlight significant capacity contributions and cost savings enabled by data center flexibility, as well as an analytical approach that can be incorporated into various planning, procurement, and market processes including integrated resource plans and transmission interconnection.