The average cost to utilities to save a kilowatt-hour (kWh) in the United States is 2.5 cents, according to the most comprehensive assessment to date of the cost performance of energy efficiency programs funded by electricity customers. These costs are similar to those documented earlier. Cost-effective efficiency programs help ensure electricity system reliability at the most affordable cost as part of utility planning and implementation activities for resource adequacy. Building on prior studies, Berkeley Lab analyzed the cost performance of 8,790 electricity efficiency programs between 2009 and 2015 for 116 investor-owned utilities and other program administrators in 41 states. The Berkeley Lab database includes programs representing about three-quarters of total spending on electricity efficiency programs in the United States.