Purpose Although the division of unpaid household labor has been studied as a driver of global gender inequity, the cognitive dimension of household labor—planning, anticipating, and delegating household tasks—has received less empirical investigation. Cognitive household labor represents a form of invisible and often unacknowledged domestic work that has been challenging to measure. Methods Within 322 mothers of young children, we assessed the division of both cognitive (“planning”) and physical (“execution”) household labor within 30 common household tasks using a self-report measure. Results We found that while mothers did more of the overall domestic labor than their partners, the division of cognitive labor was particularly gendered, such that women’s share of cognitive labor was more disproportionate than physical household labor. We found that cognitive labor was associated with women’s depression, stress, burnout, overall mental health, and relationship functioning. Conclusions This study is one of the first to investigate cognitive labor quantitatively, and the first to investigate cognitive and physical dimensions within the same household tasks. Understanding how cognitive labor affects mothers’ mental wellbeing has important implications for both practice and policy.