The new overhead calculation is Total Capacity - Configured Capacity, the description of total cpacity in vCenter shows Total amount of memory reservation used by and available for powered -on virtual machines and vSphere services on the host. The new overhead model is basically taking the amount of memory that is left over after accounting for all the memory being consumed by virtual machines, vSphere services on the host, and VMkernel core functionality, such as device drivers and other internal uses and subtracting that from the configured capacity.