Duty Cycle Calculator
Duty cycle is the single number that describes how much of each cycle a switching signal spends turned on, and it is the heart of pulse-width modulation, the technique behind LED dimmers, motor speed controllers and switching power supplies. A signal that is high for half of every cycle has a 50% duty cycle; one that is high for only a fifth has a 20% duty cycle. Because average power flows only while the signal is on, the duty cycle directly sets the average output: dial it up and the LED glows brighter or the motor spins faster, dial it down and they ease off. This calculator computes it for you. Enter the on time, how long the signal stays high in one cycle, and the full period, the total length of that cycle, both in the same unit, and the tool returns the duty cycle as a percentage along with the off-time fraction. Since duty cycle is a pure ratio, the unit you choose for the two times does not matter as long as it is consistent, because the units cancel. It is the everyday tool for setting up or reading a PWM signal. A worked example below reconciles exactly to the calculator default.
Duty cycle is the on time as a share of the period: duty cycle = (on time / period) x 100. An on time of 2 ms in a 10 ms period is a duty cycle of 20.00%, delivering about a fifth of full-on power.
Duty cycle formula
duty cycle = (on time / period) x 100
on time = time the signal is high in one cycle
period = total length of one cycle
both times in the same unit (ratio is unitless)
The on time divided by the period gives the fraction of each cycle spent on. Multiplying by 100 expresses that fraction as a percentage.
Worked example
A pulse that is on for 2 milliseconds within a 10 millisecond period.
- duty cycle = (on time / period) x 100.
- duty cycle = (2 / 10) x 100.
- duty cycle = 0.2 x 100 = 20.00%.
- The off-time share is the remaining 80.00%.
These are the calculator's default inputs, so the result above matches the widget exactly.
Duty cycle calculator: frequently asked questions
What is duty cycle?
Duty cycle is the fraction of one full period that a signal spends in its on, or high, state, expressed as a percentage. A signal that is on for half of each cycle has a 50% duty cycle. It is the key parameter in pulse-width modulation, where varying the duty cycle controls average power.
How does duty cycle control power?
In pulse-width modulation, a switch turns on and off rapidly. The average power delivered is proportional to the duty cycle, because power flows only during the on time. A 20% duty cycle delivers roughly a fifth of the full-on power, which is how LED dimmers and motor speed controllers work.
Does the period have to be in any particular unit?
The on time and the period must be in the same unit, whether seconds, milliseconds or microseconds, because duty cycle is a ratio and the units cancel. As long as both values share a unit, the percentage comes out correct regardless of which unit you chose.
What is a 100% or 0% duty cycle?
A 100% duty cycle means the signal is always on, a steady high with no off time. A 0% duty cycle means it is always off. Useful pulse-width modulation lives between these extremes, where adjusting the duty cycle smoothly varies the average output.
What is the duty cycle formula?
Duty cycle equals the on time divided by the period, times 100, to give a percentage. The on time is how long the signal stays high in one cycle, and the period is the total length of that cycle. On time of 2 over a period of 10 is 20%.
Official sources
- Time, frequency and pulse measurement standards: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.