Today, dense network deployment is being considered as one of the effective strategies to meet the capacity and connectivity demands of the fifth-generation (5G) cellular system. Among several challenges, energy consumption will be a critical consideration in the 5G era. In this direction, base station (BS) on/off operation (sleep mode) is an effective technique for mitigating the excessive energy consumption in ultradense cellular networks. However, the current implementation of this technique is unsuitable for dynamic networks with fluctuating traffic profiles because of coverage constraints, quality-of-service (QoS) requirements, and hardware switching latency. To address this, we propose an energy/load proportional approach for 5G BSs with control/data plane separation. The proposed approach depends on a multistep sleep mode profiling and predicts the BS vacation time in advance. Such a prediction enables selecting the best sleep mode strategy while minimizing the effect of BS activation/reactivation latency, resulting in significant energy savings.