RC Time Constant Calculator — Charge, Discharge & Tolerances
Explore capacitor charge and discharge, time to a voltage threshold, and timing ranges from resistor and capacitor tolerances.
See when a capacitor reaches your voltage threshold, and how resistor and capacitor tolerances change the timing. Ideal series RC step response.
Time to reach 3 V
0.916291 sR/C tolerance range: 0.696381–1.15453 s
Calculated example: 10 kΩ, 100 µF, 0 → 5 V. Loading interactive controls…
The circuit behind the curve
R 10,000 Ω · C 0.0001 F · source 5 V · initial capacitor 0 V
Follow the voltage over time
Solid line: nominal values. Shaded band: R/C tolerance extremes. The dashed horizontal line is your target; the dot marks the probe time.
Numerical voltage table
| Time | Nominal voltage | Tolerance range |
|---|---|---|
| 0 s (0τ) | -0 V | -0–-0 V |
| 1 s (1τ) | 3.1606 V | 2.73905–3.65869 V |
| 2 s (2τ) | 4.32332 V | 3.97762–4.64018 V |
| 3 s (3τ) | 4.75106 V | 4.53769–4.90347 V |
| 4 s (4τ) | 4.90842 V | 4.79095–4.97411 V |
| 5 s (5τ) | 4.96631 V | 4.90547–4.99305 V |
What the model includes
τ = RC. Voltage at time t is Vfinal + (Vinitial − Vfinal) × exp(−t/τ). One time constant covers about 63.2% of the change. Five time constants cover about 99.33%; the exact final voltage is approached asymptotically.
Timing ranges use the independent minimum and maximum R/C values. They exclude threshold uncertainty, leakage, temperature effects, ESR, changing loads and constant-current charging. Current is signed toward the capacitor; power is the initial nominal resistor dissipation, not a thermal rating recommendation.
This ideal calculation does not establish that a capacitor is safe to handle. Use equipment procedures and measurement for real discharge work.
