Variation in the metabolism of rattlesnakes attributable to reproductive status is critical to understanding viviparous energetic requirements and has potential implications for reproductive frequency and adaptive success in the face of changing climates. We investigated the effect of reproductive status on standard metabolic rates of female Prairie Rattlesnakes (Crotalus viridis). We utilized internal temperatures and morphometric data from a population of C. viridis at a high-elevation site in northwest Colorado to estimate average standard metabolic rates of pregnant and non-pregnant females throughout their relatively short active season, and to estimate the average standard metabolic rate of females during their extended inactive season. Based on those rates, estimated annual energy requirements for survival among pregnant prairie rattlesnakes were significantly higher than the baseline energy requirements of non-pregnant prairie rattlesnakes: pregnant females were estimated to require 1097 kJ (90% CI: 953-1241) of energy compared to an estimated 598 kJ (90% CI: 571-624) for non-pregnant females. We estimated that pregnant females’ annual energetic requirement for survival is 1.83 times greater than that of non-pregnant females (90% CI: 1.66-2.02). The energetics of reptiles, especially that of snakes, is realtivley unnderstudied compared to other wildlife; these estimated energetic budegets based on standard metabolic rates contribute to a greater knowledge base for rattlesnakes, which have uniquely low energetic requirements.