This paper presents an analytical model for calculating the output voltage and the power efficiency of multi-stage multi-output (MSMO) DC-DC converters (DDC) that use charge pump cells for boosting the voltage. Various cases such as multi-output current consumption and its effects on the output voltage and the power efficiency are studied. Based on the model, a tapered design approach is proposed that can bolster the power efficiency and lower the output voltage drop of MSMO DDCs. Moreover, a charge-pump-based DDC is introduced and designed to verify the proposed model. Simulation results using a standard high-voltage 180-nm CMOS technology affirms the accuracy of the presented model.