PoolWindow

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Pool Opening & Closing Date Calculator

Last updated: July 15, 2026 · 698 cities covered

Pick any covered U.S. city and get its full pool calendar in one card: the recommended opening date, the closing deadline, both windows, and today's estimated water temperature from the live model. Everything comes from the same NOAA 1991–2020 normals that power the city guides — this page just skips the reading.

What the results mean

Open by is two weeks before your city's 61°F crossing — the day its 7-day mean temperature reaches the threshold where unheated water starts climbing toward the 65°F algae-growth zone. Opening in that gap means cold, clean, cheap startup water and fully stocked stores. Close by is the fall deadline: ten days after the water leaves the algae zone, capped a week before the local 50% first-freeze date from the NOAA normals.

The temperature number is the site's water model — an exponentially weighted average of recent daily air temperatures (constant K = 0.12, roughly a two-week thermal memory), initialized on the past three weeks of Open-Meteo data. It describes a typical unheated, outdoor, in-ground pool to about ±5°F; heaters, covers, shade, and wind all shift the real number. Full math on the methodology page. Once you have the date, the 12-step opening how-to and the chemicals list turn it into a plan.

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