How to Calculate the Voltage of a Discharging Capacitor

The formula to calculate the voltage across a discharging capacitor is:

where VC is the voltage across the capacitor, VS is the supply voltage that is discharging the capacitor, t is the amount of time (in seconds (s)) for which the capacitor has been discharging, R is the resistance in of the capacitor circuit, and C is the capacitance of the capacitor.

Example

A 1000µF capacitor is being discharged of its 20 volts through a 1KΩ resistor and has been discharging for 5 seconds. What is the voltage across the capacitor after this time has elapsed?

So this capacitor will have a voltage of 0.134v after 5 seconds has elapsed.