MAXScanner electronics calculator
Updated 2026-09-16
555 Timer Calculator — Astable Frequency, Duty Cycle & Pulse Timing
Calculate classic 555 astable frequency, period, high/low time and duty cycle from R1, R2 and C using deterministic ideal timing equations.
Inputs
Results
Frequency 686.9976 Hz
Period 0.001455609 s
High 0.0007624619 s
Low 0.0006931472 s
Duty 52.38095%
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Your calculation, step by step
- 1.C = 100 nF = 0.0000001 F; High: tHIGH = ln(2)(R1+R2)C = 0.0007624619 s.
- 2.Low: tLOW = ln(2)R2C = 0.0006931472 s; Frequency: f = 1/(tHIGH+tLOW) = 686.9976 Hz.
Formula, example and limits
tH=ln2(R1+R2)C; tL=ln2 R2 C; f=1/(tH+tL); D=tH/(tH+tL).
1 kΩ, 10 kΩ and 100 nF produces about 687 Hz with roughly 52.4% duty.
- Classic bipolar/CMOS 555 astable topology.
- Leakage, threshold tolerance and output-stage limits are not modeled.
Frequently asked questions
Why is duty cycle above 50%?
In the classic astable circuit the capacitor charges through R1+R2 but discharges through R2.
Does supply voltage set frequency?
The ideal classic timing equation depends on R and C; real devices still have datasheet operating limits.