Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

R1 (Ω)

Required number input.

R2 (Ω)

Required number input.

Compute the output duty cycle percentage of an NE555 astable circuit from R1 and R2. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Duty cycle (%)

The resulting duty cycle returned as a number.

• Ideal 555 timing equations neglect threshold tolerance, discharge saturation, leakage, capacitor tolerance and dielectric absorption, output loading, supply variation, and the differences between bipolar and CMOS variants. Very short or long intervals need datasheet verification.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

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