This study identified which energy expenditure (EE) and dietary intake outcomes determine EE from doubly-labeled water (DLW) in U.S. older adults (n = 681; 45.9% male; mean age 63.2). A secondary data analysis using baseline data from The Interactive Diet and Activity Tracking in AARP (IDATA) study was conducted. Stepwise linear regressions identified predictor outcomes of EE from DLW within sexes. Outcomes included data from ActiGraph accelerometers, Community Healthy Activities Model Program for Seniors (CHAMPS) self-report activity questionnaire, Automated Self-Administered 24-hour dietary recall, Dietary History Questionnaire II (DHQ II), and resting EE. Energy expenditure by ActiGraph in males predicted EE from DLW (R² = 0.33, p < .001). EE from ActiGraph and total dietary fiber from DHQ II predicted EE from DLW in females (R² = 0.44, p < .001). The CHAMPS closely matched EE from DLW when considering resting EE. These findings can be used to assess energy balance in a non-invasive manner in older adults.