Capacitor Charge and Discharge Calculator

Online Calculator and Formulas to calculate the Capacitor charge and Discharge at a Specified Time


On this page you can calculate the discharge voltage of a capacitor in a RC circuit (low pass) at a specific point in time.

In addition to the values of the resistor and the capacitor, the original input voltage (charging voltage) and the time for the calculation must be specified

The result shows the charging voltage at the specified time and the time constant τ (tau) of the RC circuit. The capacitor is discharged approx. 99.33% after a period of 5 τ. This means that at specified times, well over 5 τ the charging voltage is close to zero.

Online calculator

Enter the four values in the appropriate fields.

Note the unit of measurement.



Applied voltage

Discharge time

Time constant

Charging voltage

Decimal places

Formula for calculating the discharge voltage

\(\displaystyle U_C=U_0 · e^{-\frac{t}{τ}}\)

\(\displaystyle τ=R ·C\)


\(\displaystyle R\)

Resistor (Ω)

\(\displaystyle C\)

Capacitor (F)

\(\displaystyle τ\)

Time constant (sec)

\(\displaystyle U_0\)

Applied voltage (V)

\(\displaystyle U_C\)

Charging voltage at the capacitor (V)