Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for determining a measure of resource usage by a virtual machine between startup and termination. The determination can be based on units of time in a sequence of contiguous units of time from the startup to the termination of a virtual machine. The actual utilization of a resource by the virtual machine during a unit of time may be compared to a resource utilization cap for the resource for the unit of time. If the utilization cap is exceeded, the excess resource utilization is determined. If the resource utilization cap is not exceeded, a resource utilization shortfall is determined. The measure of resource usage can be based on the number of units of time, the resource utilization cap for each resource, and the amount of excess resource utilization for each resource.