Well Pump Cycle Time Calculator
A well pump cycles on to refill the pressure tank, then off while the tank supplies water. The run time is the tank drawdown divided by the net fill rate (pump flow minus demand), and the off time is the drawdown divided by the demand. Together they set the cycle time and the cycles per hour, which tells you whether the pump is short cycling. This calculator computes all four from your drawdown, pump flow, and demand using simple, exact flow arithmetic.
Well pump cycle formula
Net fill rate = pump flow - demand
Run time = drawdown / net fill rate
Off time = drawdown / demand
Cycle time = run time + off time
Cycles per hour = 60 / cycle time
Demand must be below the pump flow rate or the pump never catches up and runs continuously. Run time fills the drawdown at the net rate; off time empties it at the demand rate. The two add to the full cycle.
Well pump cycling notes
- Drawdown is the usable water between cut-on and cut-off pressure, not the tank's total size.
- Short cycling, many starts per minute, overheats the motor and shortens pump life.
- A common guideline keeps cycles to roughly one or two per minute or fewer.
- A larger drawdown tank lengthens run and off times and reduces cycling.
- If demand equals or exceeds pump flow, the pump runs without ever cycling off.
Well pump cycling: frequently asked questions
How do I calculate well pump run time?
Run time is the tank drawdown divided by the net fill rate, which is pump flow minus demand while the pump runs. Off time is the drawdown divided by demand while the pump is off. For a 20 gallon drawdown, a 10 gallon-per-minute pump, and 2 gallons per minute demand, run time is 20 divided by 8, which is 2.5 minutes.
What is tank drawdown?
Drawdown is the volume of water a pressure tank delivers between the pump cut-on and cut-off pressures. It is much smaller than the tank's total size because the air charge occupies most of the tank. Manufacturers publish drawdown for each tank and pressure setting; enter that figure rather than the tank's nominal capacity.
Why does short cycling damage a pump?
Each start draws high inrush current and stresses the motor and controls. If the pump turns on and off many times per minute, called short cycling, it overheats and wears out early. A common guideline is to keep cycles to roughly one or two per minute or fewer, which a larger drawdown tank helps achieve.
What demand should I enter?
Demand is the flow being drawn during the cycle, for example a running faucet or shower. A single fixture might draw 1 to 3 gallons per minute. Enter the steady demand you want to evaluate. Demand must be less than the pump flow rate, otherwise the pump runs continuously and never cycles off.
What is a full cycle time?
A full cycle is one run period plus one off period. Cycle time equals run time plus off time, and cycles per hour is 60 divided by the cycle time in minutes. The calculator reports run time, off time, total cycle time, and cycles per hour so you can check the pump is not short cycling.
Official sources
- U.S. Environmental Protection Agency: Private Drinking Water Wells.
- U.S. National Institute of Standards and Technology: Unit conversion (gallon, minute).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.