A capacitor never gets charged to 100%. But you can calculate the time taken to charge the capacitor using the capacitor time constant which is calculated by multiplying R and C (tau = R * C). It takes about 5 times the time constant for a capacitor to reach 99% charged. The higher the resistance or capacitance, the longer it takes to charge
After 5 time constants, the capacitor will charged to over 99% of the voltage that is supplying. After 5 time constants, for all extensive purposes, the capacitor will be charged up to very close to the supply voltage. A capacitor never charges fully to the maximum voltage of its supply voltage, but it gets very close.
Charging a capacitor is not instantaneous. Therefore, calculations are taken in order to know when a capacitor will reach a certain voltage after a certain amount of time has elapsed. The time it takes for a capacitor to charge to 63% of the voltage that is charging it is equal to one time constant.
The time constant When a capacitor is charging or discharging, the amount of charge on the capacitor changes exponentially. The graphs in the diagram show how the charge on a capacitor changes with time when it is charging and discharging. Graphs showing the change of voltage with time are the same shape.
(A short circuit) As time continues and the charge accumulates, the capacitors voltage rises and it's current consumption drops until the capacitor voltage and the applied voltage are equal and no current flows into the capacitor (open circuit). This effect may not be immediately recognizable with smaller capacitors.
Practically the capacitor can never be 100% charged as the flowing current gets smaller and smaller while reaching full charge, resulting in an exponential curve. This is why after a number of five multiples of the time constant, we regard the capacitor as fully charged. We'll explain the notion of time constant in the next section.