Turnover is the whole game
A pump's job is simple: move every gallon through the filter about once a day. Time for one turnover is just volume divided by real-world flow. A 15,000-gallon pool at 55 gallons per minute turns over in about four and a half hours — running that pump 12 hours "to be safe" filters the same water three times and pays for the privilege.
turnover hours = gallons ÷ (GPM × 60) · monthly cost = watts × hours/day × 30 ÷ 1000 × $/kWh
Cheap circulation rules
Run longer at lower speed if your pump allows it — power falls with the cube of speed, so slow filtration is dramatically cheaper per gallon filtered. Schedule runs during chemical additions and daytime algae-growing hours, shift what you can to off-peak rates, and shorten runtimes in the off-season when demand on the water is low. If you're sizing a new system, get the volume right first with the volume calculator.
Frequently asked questions
How many hours a day should a pool pump run?
Long enough to push the whole pool through the filter once — a "turnover." One turnover a day keeps most residential pools clear; heavy use, heat waves, or algae recovery justify two. In practice that lands around 6–10 hours in summer and half that off-season, but your own turnover time (volume ÷ flow) is the honest number, and it's what this calculator computes.
Do I have to run it all at once?
No — split runs work fine and often cost less on time-of-use electricity rates. What matters is total daily circulation, plus running during chemical additions and (for salt pools) enough runtime for the generator to make its daily chlorine.
Is a variable-speed pump worth it?
Usually, and by a lot. Pump power falls with the cube of speed: half speed uses about one-eighth the power while still moving half the water — so a slow 12-hour run filters the same water for a fraction of the cost of a fast 6-hour one. Many US states now effectively require variable-speed on new installs; if your single-speed pump is due for replacement, the electricity math almost always favors the upgrade.
How do I know my pump's real flow rate?
The honest sources, best to worst: a flow meter on the return line; your filter's pressure and the pump's flow curve; or the ballpark this calculator uses (a typical residential setup delivers roughly 40–60 GPM per horsepower after plumbing losses). Nameplate "max flow" is a lab number your plumbing will never see.