For state-of-the-art RF MEMS capacitive switches, a dielectric-charging model was constructed to predict the amount of charge injected into the dielectric and the corresponding shift in actuation voltage. The model was extracted from measured charging and discharging transient currents on the switch dielectric under different control voltages. The model was verified against the actuation-voltage shift under different control waveforms. Duty factor and peak voltage of the control waveform were found to be critical acceleration factors for the charging effects while actuation frequency is not an acceleration factor. The model is capable of predicting the actuation-voltage shift under complex control waveforms such as the dual-pulse waveforms. For RF MEMS capacitive switches that fail mainly due to dielectric charging, the model can be used to design control waveforms that can either prolong lifetime or accelerate failure.