This paper presents a framework for estimating the future Nth-of-a-kind (NOAK) cost of advanced low-carbon technologies that are currently at early pre-commercial stages of development. It identifies two types of question that commonly motivate a cost analysis: “What If” questions about the hypothetical future cost of a technology that meets specified R&D goals or requirements; and “What Will” questions regarding the true expected cost of an advanced technology once it is mature and widely deployed. The latter type of question is the focus of this paper. It addresses shortcomings in the “bottom up” engineering-economic method current used to estimate NOAK costs. It describes a more rigorous hybrid costing method that combines a bottom-up analysis of the first-of-a-kind (FOAK) commercial cost of an advanced technology with an empirical model employing experience curves to project its future cost. Guidelines are presented for all phases of the analysis.