This paper studies voltage regulation and optimal current sharing problems of single-bus islanded direct current (DC) microgrids. A novel prescribed-time multiple-stage control algorithm is proposed for restoring the bus voltage and minimizing the total current generation cost in a prescribed time T. The prescribed time T can be pre-designed arbitrarily if it is physically feasible. The algorithm consists of three successive stages with durations $T_{\textrm {1}}$ , $T_{\textrm {2}}$ and $T_{\textrm {3}}$ , respectively, satisfying $T_{\textrm {1}} + T_{\textrm {2}}+ T_{\textrm {3}}=T$ . Specifically, in the first stage, the total load current is estimated by a distributed prescribed-time estimator. In the second stage, a prescribed-time tracking control algorithm is introduced for achieving the voltage regulation and supply-demand balance. In the third stage, the optimal current sharing is achieved through a distributed consensus-based prescribed-time control algorithm. The proposed algorithm allows the dynamics of bus voltage and output currents to be decoupled from each other, allowing the separate operation of voltage regulation and optimal current sharing and facilitating the analysis. Moreover, the proposed algorithm can also accomplish the traditional objectives of voltage regulation and proportional current sharing by re-defining the current tracking errors and removing the third stage. Finally, several simulations are conducted to demonstrate the effectiveness of the designed algorithm.