Normalization of a network performance index is achieved. Data is stored that groups devices in a network into groups or families according to their estimated life cycles. Data is stored representing a group-specific time window based on the estimated life cycle for devices in that group. Data is stored representing a count of the number of devices in the network within each group during a given unit of time, dynamic sliding windows over successive units of time. A sliding window group count is generated that represents the number of devices within each group in the network as of a current unit of time and prior units of time within the group-specific time window. A total group count is generated by adding the dynamic sliding window group counts for each of the groups. A normalized network performance index is generated by dividing a network performance index by the total group count.