Economic analysis of energy efficiency programs, utility resource planning, and procurement require estimating how long energy savings last. We analyzed program-level gas and electric efficiency data reported by more than 100 utilities and other program administrators in 41 states to produce distributions of program lifetimes and active savings curves. We find that most gas and electricity savings expire within 15 years of initial program investment, with the trajectory varying by fuel and market sector. Program design and the technologies addressed by programs drive these differences. In particular, residential electricity savings decline more quickly than commercial and industrial (C&I) savings due to the expiration of behavioral and lighting measures. We also find that gas savings are longer lived than electricity savings for all sectors but C&I. Finally, we consider the relevance of active savings curves and program lifetime distributions to resource planning and assessing energy efficiency program performance.