The IEEE 802.15.4 standard does not allow to make dynamic adjustments to the inactive portion of the superframe, thus affecting the duty cycles of the coordinator and all the devices attached to it. Prior works in this direction are either based on superframe occupation ratio or buffer occupancy/queue length of the transmitting nodes. In this paper, we present the respective limitations of both these schemes that lead to sub-optimal MAC parameter (BO and SO) settings and later propose a dynamic duty cycling mechanism based on MAC parameters (macMinBE, macMaxCSMABackoffs and macMaxFrameRetries). A Markov model is developed for IEEE 802.15.4 CSMA-CA that is used to analytically estimate the delay and energy consumption during transmission of frames using the MAC parameters.