Cities have a clear and fundamental role to play in addressing the climate emergency and achieving the UN Sustainable Development Goals. Many are working hard to decarbonise, but face significant challenges due to inertia in existing systems, pre-existing policy environments, and limited budgets. A key obstacle is the seemingly high cost of reshaping key CO2-emitting sectors in the city, from transport, to buildings, to the power supply, as well as challenges in understanding who needs to pay and who stands to benefit. This makes decision-makers hesitant to pursue change. However, many recent global reports show clear economic opportunities in decarbonisation that are often attractive for multiple reasons, including improved public health and other co-benefits. The problem for city leaders is how to translate those analyses, which are often generic, into estimates of the economics of change for individual cities.