Provided is a computer system including a storage subsystem, a host computer, and a management computer for managing the storage subsystem and the host computer. The storage subsystem manages a storage extent by a group unit and creates storage extent configuration information. The management computer stores group management information, obtains the storage extent configuration information, calculates an assigned capacity for each group based on the obtained storage extent configuration information, forecasts a capacity to be assigned in the future for each group based on the calculated assigned capacity, calculates a protection term expired capacity for each group based on the group management information and the storage extent configuration information, and outputs the assigned capacity, the capacity to be assigned in the future, and the protection term expired capacity. Thus, the storage extent of the storage subsystem can easily be managed.