Primates have markedly lower total energy expenditure (TEE; kcal/day) than other placental mammals, expending approximately 50% less energy for their mass than non-primate eutherians. However, little is known regarding interspecific variation of energy expenditure within platyrrhine primates. We investigated TEE in captive tufted capuchins (Sapajus apella, n = 8, ages 7–36), a frugivorous platyrrhine, to compare TEE with other placental mammals and primates. We tested the hypothesis that large-brained capuchins would exhibit greater TEE than other platyrrhines that are less encephalized. We used the doubly labeled water (DLW) method to measure TEE over 7–11 days, during which physical activity data were recorded via focal observation. TEE was strongly correlated with fat free mass, but sex, age, and rates of walking and climbing were not correlated with variation in TEE in multivariate analyses controlling for fat free mass. We found evidence that daily physical activity was negatively correlated with body fat percentage. Capuchin TEE was similar (P = 0.67) to other, less encephalized platyrrhines (Callithrix and Alouatta) and 54% lower than other placental mammals, in analyses controlling for body mass. These results suggest that brain size and physical activity do not necessarily influence variation in daily energy expenditure across primate species.