The National Nuclear Security Administration (NNSA) manages and secures the nation's nuclear weapons stockpile, with annual appropriations of about $6.4 billion. NNSA oversees eight contractor-operated sites that execute its programs. Two programs make up almost one-third of this budget: Readiness in Technical Base and Facilities (RTBF) Operations of Facilities, which operates and maintains weapons facilities and infrastructure, and Stockpile Services, which provides research and development (R&D) and production capabilities. Consistent with cost accounting standards, each site has established practices to account for these activities. The Administration has recently committed to stockpile reductions. GAO was asked to determine the extent to which NNSA's budget justifications for (1) RTBF Operations of Facilities and (2) Stockpile Services are based on the total costs of providing these capabilities. GAO was also asked to discuss the implications, if any, of a smaller stockpile on these costs. To carry out its work, GAO analyzed NNSA's and its contractors' data using a data collection instrument; reviewed policies, plans, and budgets; and interviewed officials. Among other things, GAO recommends that NNSA develop guidance for consistent collection of total cost information and use this information for budget formulation and program planning. NNSA agreed with the report's findings and recommendations.