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Capacitor Discharge Calculator — RC Voltage, Current & Time Constant
Calculate exponential capacitor-discharge voltage and current at an entered elapsed time, plus the RC time constant and five-time-constant reference.
Last updated: September 16, 2026
Results
Time constant 1 s
Voltage at t 4.414553 V
Current at t 0.4414553 mA
5τ 5 s
Formula, example and assumptions
V(t)=V0·e^(-t/RC); I(t)=V(t)/R; τ=RC.
100 µF through 10 kΩ has τ=1 s and falls to about 0.67% after 5τ.
- Ideal resistor-capacitor discharge with constant R and C.
- Leakage, ESR, dielectric absorption and voltage-dependent capacitance are not modeled.
Frequently asked questions
When is a capacitor fully discharged?
Mathematically never exactly; 5 time constants leaves about 0.67% of the starting voltage.
Does this size a bleeder resistor?
No. This page evaluates a resistance you enter. For safety-critical bleeder design, solve the required resistance separately and verify power and voltage ratings.