Systems and methods for managing demand for virtual computing resources are disclosed. A demand forecasting service can obtain and analyze historical demand data for purposes of predicting future demand. The analysis includes identifying untargeted demand corresponding to requests for virtual machine instances that can be fulfilled by any availability zone of a set of zones. The demand forecasting service may provide predictions of future demand including information regarding future untargeted demand, thereby enabling efficient allocation of computing resources among various availability zones to meet the future demand.