Mohenjo-daro was a major city of the Indus Civilisation (c. 2600–1900 BC), with excavations revealing evidence for public infrastructure, civic amenities and hundreds of residences. Archaeologists traditionally assume that urbanism is accompanied by economic stratification, but, at Mohenjo-daro, qualitative evidence of inequality is absent. Drawing on early excavation data, the authors here calculate Gini coefficients of residence area, providing a quantitative proxy of economic inequality. Their results indicate that Gini coefficients, and thus inequality, declined over time, coinciding with increased prosperity and the development of the city’s street plan, indicating that governance likely helped limit economic inequality.