When to Close Your Pool: Estimated Dates for Your City and State

Close your pool once the water stays below about 65°F, or below 60°F for the lowest risk of a green pool in spring, and finish before freezing nights put the plumbing at risk. Across most of the Northeast and Midwest that means mid-September to mid-October; the Mid-Atlantic and Ohio Valley run to mid- or late October; much of the South can wait until November or later.

Most guides stop at the temperature. We added dates: the day the typical daily mean air temperature drops below 65°F and 60°F in 46 US cities, from NOAA’s 1991–2020 climate normals, including the ten states people search for most. These are air-temperature estimates. Pool water cools later, so treat each date as the day to start checking your thermometer.

The closing temperature: 65°F or 60°F?

A pool retailer and a cover maker give the same number. Doheny’s Pool Supplies puts it plainly:

Avoid closing your pool until your water temperature readings consistently drop below 65°F.

Anchor Industries, which makes safety covers, uses the same 65°F (18°C) figure.⁴ The reason is algae: close while the water is warm and algae keeps growing under the cover, using up winter chemicals and leaving a cleanup job in spring. Winterizing doses are per gallon, so check your size first with the pool volume calculator.

The Trouble Free Pool forum sets a stricter bar in its Pool School closing procedure:

Wait to close until the water temperature is solidly below 60 degrees.

Below 60°F, it explains, algae is fairly unlikely to grow, and grows very slowly when it does.² Both rules mean water temperature over several days.

Choose 65°F for a longer season, 60°F for a cleaner spring opening. The freeze deadline is the one you can’t miss.⁸

When to close your pool: estimated dates by city

We placed each NOAA monthly normal at the middle of its month, joined the months day by day, and found the first fall day the typical daily mean air temperature drops below 65°F and below 60°F.¹ The frost column is the median date of the first 32°F night at the nearest station; half of years see it earlier.

Seattle crosses 65°F by early September but has no median frost until mid-November: a long, cool window. Denver’s median frost (Oct 12) comes 12 days after its 60°F date, leaving little slack. In Phoenix and Houston the air stays above 60°F into late November or December and frost is rare or late; PoolResearch and River Pools both note that many owners in the warmest states never close.^9,8 For any other ZIP code, look up your first-frost date and its odds.

Why your water cools later than the air

The USGS explains that water absorbs a lot of heat before it gets hot, which is why seasons change gradually near large bodies of water.⁶ A pool does the same on a small scale: it carries late-summer heat into fall, so the water reaches 65°F or 60°F some days after the air does. How many depends on depth, sun, wind, a solar cover and any heater.

Plan with the table, then let a thermometer decide: read the water at the same time each day and close after several days in a row below your line. Doheny’s adds a forecast test: wait until temperatures below 65°F are forecast for the weeks ahead, not just a cool spell.³

The other deadline: freezing nights

Anchor Industries warns that freezing water can crack pipes and damage filtration equipment,⁴ and River Pools advises closing before nights fall under 30°F.⁸ Our frost date tool also shows the date with only a 10% chance of an earlier frost, the safer target if you close late. If a hard freeze is forecast before you are ready, follow the freeze-protection instructions in your pump and heater manuals.

When to close a pool in NJ, NY, PA, MI and six more states

These ten states lead Google’s search suggestions for this question. Inland and higher ground usually runs earlier than a coastal or big-city station.

New Jersey

North Jersey and the Delaware Valley reach the 65°F air mark around Sep 22–26 and 60°F around Oct 4–8. The shore runs about a week later: Atlantic City crosses 60°F near Oct 14, with a median frost of Nov 21. Carlton Pools says New Jersey owners typically close from late September to mid-October.¹¹

New York

Upstate runs about two weeks ahead of the city: Buffalo and Albany cross 60°F by about Sep 25, New York City and Long Island in early October. Central Park’s median first frost isn’t until Nov 20.

Pennsylvania

Erie, Harrisburg and Pittsburgh cross 60°F around the start of October. Philadelphia, whose station is at the Franklin Institute in Center City, is about two weeks later. Erie cools on Harrisburg’s schedule, but its median frost comes 12 days later.

Michigan

Michigan is earliest: the typical daily mean drops below 65°F around Aug 27 in Traverse City, Sep 4 in Grand Rapids and Sep 17 in Detroit.

Ohio

Cleveland, Columbus and Cincinnati all cross 65°F between Sep 20 and 24 and 60°F in the first week of October. The deadline differs: the Cleveland lakefront station’s median frost is Nov 12, nearly three weeks after Columbus.

Massachusetts

Worcester crosses 65°F around Sep 4 and Springfield around Sep 9; Boston is about two weeks behind. SSG Pools, a New England builder, says most owners there close between late September and mid-October.¹⁰

Connecticut

Hartford, New Haven and Stamford are nearly identical: about Sep 19 for 65°F and Oct 1–2 for 60°F.

Maryland

Maryland runs latest of the ten states. Frederick crosses 60°F around Oct 11 and Baltimore’s Inner Harbor station around Oct 19, so mid-October closings are realistic.

Illinois

Rockford reaches 60°F around Sep 27; Chicago and Springfield around Oct 4. Chicago’s temperatures come from Midway airport and its frost date from a lakefront station, where frost comes later than in inland suburbs.

Indiana

South Bend and Indianapolis cross 60°F between Sep 28 and Oct 2. Evansville is nearly three weeks later.

Do the dates match published regional advice?

Yes. Every published window below starts on or after our 65°F air dates, and most end within about two weeks of our 60°F dates, consistent with water cooling later than the air. None of these guides gives a date for a specific city.

Other signs it’s time, and the cost of getting it wrong

• Falling leaves. Anchor Industries calls a considerable amount of leaves falling into the pool a clear sign it’s time to close.⁴
• Too early (water above 65°F): Doheny’s lists algae, stained surfaces, cloudy water and a costlier spring opening.³
• Too late (after a hard freeze): water left in pipes, the pump, filter or heater can freeze and crack them.⁴

Closing steps at a glance

Every pool, cover and equipment pad is different, so treat this as an overview and follow your equipment and cover manuals.

1. 1

   Balance the water

   Trouble Free Pool’s procedure brings pH to 7.4–7.6 and alkalinity and calcium hardness into their normal ranges.² Our guide to ideal pool chemical levels explains each number.

   

2. 2

   Raise the chlorine

   Shock or raise chlorine to the closing level your product label or method specifies, a day or more ahead. Add any winter algaecide only as its label directs.

3. 3

   Clean the pool

   Brush, skim and vacuum, then store ladders, rails and toys.

4. 4

   Lower the water only as far as your cover allows

   Trouble Free Pool notes that safety-cover makers set a maximum water depth below the deck, and that draining a pool under an automatic cover can damage it.⁷ Check your cover manual first.

   

5. 5

   Clear water from plumbing and equipment

   Water left in lines, the pump, filter and heater can freeze. Methods vary by system, so follow each manufacturer’s winterizing instructions or hire a pool service. For a hot tub, see how to winterize a hot tub.

6. 6

   Cover the pool

   Fit the winter or safety cover as its maker instructs, and check it through the winter for loose weights, standing water and leaves.

   

Add pool chemical to water, NEVER water to pool chemicals.

This guide is general information, not professional advice; your manuals and product labels come first. See our estimates and safety disclaimer.

Next steps

Set your ZIP code above to see your first-frost date, and put two reminders in your calendar: your 65°F date, and two weeks before your frost date. Then browse the opening and closing section, the pool salt calculator and the rest of Pool & Spa; our methodology and climate data pages explain the numbers.