The Climate Equity Reference Project (CERP) framework (formerly GDRs) allocates responsibility for greenhouse gas mitigation and adaptation based on individual responsibility for historical emissions and capacity to act. The Climate Equity Reference Calculator (CERc) is a web-based tool for exploring how specific user-defined quantitative expressions of the CERP framework affect allocations. This paper documents the calculations that the calculator implements, while the web interface is described in a separate publication.