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RC Response and Threshold Time Calculator

Calculate capacitor voltage after a step or time to a threshold using actual initial and final voltages; distinguish unreachable and asymptotic targets.

Use this result well

Inputs that matter
Thevenin resistance seen by capacitor (ohm), Capacitance (microfarad), Initial capacitor voltage (V), Final capacitor voltage (V), and 3 more
Output to expect
RC voltage after elapsed time, RC time to a target voltage
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

RC voltage after elapsed time

Evaluate a first-order capacitor response using the actual initial and final voltages and Thevenin resistance. Loading, leakage, tolerances and higher-order behavior need a separate circuit model.

τ = R × C; V(t) = Vf + (Vi − Vf) × exp(−t / τ). A single-pole cutoff is 1 / (2πRC).

RC time to a target voltage

Find the first time an ideal first-order response reaches a specified threshold. Targets beyond the initial-to-final interval are unreachable; the final voltage is approached asymptotically.

t = −RC × ln((Vtarget − Vf) / (Vi − Vf)) for an interior threshold.

Updated: September 2026

Example Scenarios

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ 3.160603 V at 1 s

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ 1.609438 seconds to threshold

FAQ

Evaluate a first-order capacitor response using the actual initial and final voltages and Thevenin resistance. Loading, leakage, tolerances and higher-order behavior need a separate circuit model. Find the first time an ideal first-order response reaches a specified threshold. Targets beyond the initial-to-final interval are unreachable; the final voltage is approached asymptotically.

Use the exact equipment data, measurement point, operating conditions and units described in the selected mode. Record source documents, dates and unresolved conditions in Sources and assumptions. Built-in examples illustrate arithmetic; they are not manufacturer ratings or approved designs.

Use Save planning case for an explicit local history entry. Copy MD keeps current inputs and notes; Download CSV exports the result breakdown. Export portable copies before clearing storage and save a separate case after changing equipment, conditions or measurements.

About RC Response and Threshold Time Calculator

Evaluate a first-order capacitor response using the actual initial and final voltages and Thevenin resistance. Loading, leakage, tolerances and higher-order behavior need a separate circuit model. Find the first time an ideal first-order response reaches a specified threshold. Targets beyond the initial-to-final interval are unreachable; the final voltage is approached asymptotically.