Cost per swim, and why it is the only number that settles the argument

The arithmetic, and why nobody does it

Every discussion of pool costs stops at the annual figure, which is exactly one step short of useful. An annual figure is a number without a unit of value attached. Divide it by the number of times somebody actually got in the water and you have something you can compare against a cinema ticket, a swim pass or a takeaway.

The same pool, at four different levels of use

Hold the running cost constant and vary only how often anyone gets in. This is the table that changes people’s minds, in both directions.

The spread is a factor of ten, and none of it is about the pool. It is entirely about whether the thing gets used, which is a question about your household, your weather and how much friction stands between deciding to swim and being in the water.

Counting swims honestly

The mistake is counting intentions. Before buying, most families picture daily use through the summer; in practice the number is set by weather, work, and how much effort the pool takes on a Wednesday evening.

A more honest way to estimate it: count the days last summer when it was hot enough that you would definitely have got in, then halve it for the ones where something else came up. That number, not the optimistic one, is what to divide by. If the honest answer is under fifteen, our are they worth it page is the right one to read before buying anything.

Year one versus year two, which is a different question

The table above is a year-two number, and that is deliberate. In year one you are also buying the pool, the pump, the ladder, the ground cloth, the covers, the net and the dispenser, and none of those recur. Loading the whole purchase onto a single season’s swims produces a figure that flatters a membership and misrepresents the pool.

The fair way is to spread the durables across the seasons you actually expect to get. Our year two guide sorts every line into one-off and recurring, and pool versus membership uses the same framing to make that comparison work across several summers rather than one.

How the pool size changes it

Larger pools cost more to run, permanently, but they also tend to get used more — they are more comfortable with several people in, and deeper water is more appealing to adults. So the effect on cost per swim is not as one-sided as the running-cost table suggests.

Electricity figures assume 8 hours a day for 120 days at the EIA US residential average of 18.34 cents per kWh, and the wattages are illustrative because manufacturers in this category publish flow rates rather than power draw — read the label on your own pump, as our pump electricity guide explains.

The two ways to improve the number

Raise the denominator. Extend the season at both ends with a solar cover — it is the highest-return item in this hub and it works by making the water warm enough to use in May and September, which is pure denominator. Our season extension guide covers the cheap methods before the expensive one.

Lower the numerator, carefully. A timer on the pump is the honest saving; most of the others are marginal on a pool this size. Our energy saving guide ranks the measures by what they genuinely return rather than by how good they sound.

Note which of those two is bigger. Cutting two hours a day off a 300 W pump saves about $13 across a season. Getting fifteen more swims out of the same pool moves the cost per swim far more than that, and it is more fun.

What the number is actually for

Not to justify the pool after the fact. It is to answer a specific question honestly before you buy: is the amount this household will genuinely use a pool large enough to make the running cost sensible?

For a family with children and a hot summer, the answer is usually a clear yes and the per-swim figure is trivially small. For two adults who work long hours in a cool climate, it can genuinely be no, and our membership comparison is the alternative worth pricing. Both answers are respectable; the mistake is never doing the division.