How much does it cost to run a 400-gallon hot tub per month?

Data checked October 2026

Short answer

A 400-gallon hot tub that meets California's standby limit costs about $40.27 a month to keep at 102°F — $483 a year (2,656 kWh) at the U.S. average 18.19¢/kWh.

California Title 20 caps a hard-shell spa's standby power at 3.75 × V^(2/3) + 40 watts: 244 W for 400 gallons, measured covered with water at 102°F and normalized to a 37°F water–air gap.
Outdoors it peaks in January at $59.06 and falls to $24.00 in the warmest month (U.S. population-weighted normals).
Turning the water down 2°F to 100°F saves about $20.98 a year.
The inflatable limit for the same volume is 380 W — inflatable spas are allowed to lose more heat.
Soaks with the cover off add more. Industry estimates for a full year of use run 1,500–3,500 kWh; many tubs also test well under the legal cap, so enter your tub's listed standby watts for a closer figure.

Adjust it to your exact job

Your hot tub

Type

Fill volume

gal

On the spec sheet or the tub's California Energy Commission listing (filled to mid-skimmer).

Standby power

Title 20 caps how much a covered spa may draw just to stay hot. Many tubs test well under the cap.

Settings

Water temperature

°F

Location

Electricity rate

Where the tub is

Price per kWh

EIA's state average: total residential revenue ÷ kWh sold, so delivery and fixed monthly charges are spread over every kWh.

400-gallon hot tub costs

$40.27a month on average

2,656 kWh a year · January up to $59.06 · $1.32 a day

At 18.19¢/kWh — U.S. average, Jan–Aug 2026 (EIA).

Per year: $4832,656 kWh
Coldest month (Jan): $59.06air 36°F
Standby rating: 244Wat a 37°F water–air gap
Average draw: 303Win an average U.S. climate

Monthly cost outdoors in an average U.S. climate

Turn it down a notch

Yearly cost by water temperature
Water	Per year	vs 102°F
98°F	$441	−$41.96
100°F	$462	−$20.98
102°F	$483	—
104°F	$504	+$20.98

What this includes

Keeping the covered tub at temperature, with its default filtration cycles — the condition California tests. Soaks with the cover off and jets running add more on top; industry estimates for a full year of use run 1,500–3,500 kWh.

Using the legal maximum

244 W is the most a 400-gallon hard-shell spa sold in California may draw in standby. Enter your tub's listed rating for a closer figure.

How to cut it

Keep the cover on and replace it once it's waterlogged or sagging — the cover is part of the tested rating.
Heat loss grows with the gap between water and air: each degree lower saves roughly the share shown in the table.
Most of the year's cost lands in the coldest months — an enclosed or indoor tub sees a smaller gap; switch Location to compare.

Energy budget

2,656 kWh 400-gallon hot tub — keeping it hot for a yearcovered standby at 102°F, 18.19¢/kWh$483

Estimated total$483

Did this answer your question?

Compare

The same tub in colder and warmer states, at each state's Jan–Aug 2026 rate

State	¢/kWh	kWh a year	Per year	Coldest month
Minnesota	16.44	3,441	$566	$74.47
Colorado	16.8	3,261	$548	$63.33
New York	29.26	3,002	$878	$107.95
Ohio	18.81	2,961	$557	$69.72
Washington	14.42	2,974	$429	$46.11
Texas	16.03	2,031	$326	$42.20
California	32.58	2,407	$784	$83.85
Arizona	15.36	2,023	$311	$39.70
Florida	15.32	1,703	$261	$30.57

How this was worked out

400^(2/3) = 54.3; × 3.75 + 40 = 244 W at a 37°F gap. Heat loss through the cover and shell scales with the gap, so each month we multiply by (102°F − average outdoor temperature) ÷ 37 and by the hours in the month.

Prices: EIA average residential rates for Jan–Aug 2026. Outdoor temperatures: NOAA Climate Prediction Center population-weighted normals.

The full method, material data and tips are on the main hot tub cost calculator page.

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Sources

Data behind this answer

California Energy Commission — Title 20 portable electric spa standard (Docket 18-AAER-02) — max standby 3.75·V^(2/3)+40 W (standard spas), 7·V^(2/3) (inflatable), normalized to a 37°F water–air difference · checked October 2026
EIA Electric Power Monthly, Tables 5.6.A & 5.6.B — residential price by state (August 2026) — latest month and Jan–Aug 2026 year-to-date average for every state; preliminary, refreshed monthly · checked October 2026
NOAA Climate Prediction Center — population-weighted state degree days — monthly normal heating and cooling degree days by state (base 65°F) · checked October 2026
EIA Electric Power Monthly technical notes — average price = revenue ÷ sales, including fixed customer charges, fuel adjustments and surcharges · checked October 2026

Short answer

A 400-gallon hot tub that meets California's standby limit costs about $40.27 a month to keep at 102°F — $483 a year (2,656 kWh) at the U.S. average 18.19¢/kWh.

California Title 20 caps a hard-shell spa's standby power at 3.75 × V^(2/3) + 40 watts: 244 W for 400 gallons, measured covered with water at 102°F and normalized to a 37°F water–air gap.

Outdoors it peaks in January at $59.06 and falls to $24.00 in the warmest month (U.S. population-weighted normals).

Turning the water down 2°F to 100°F saves about $20.98 a year.

The inflatable limit for the same volume is 380 W — inflatable spas are allowed to lose more heat.

Soaks with the cover off add more. Industry estimates for a full year of use run 1,500–3,500 kWh; many tubs also test well under the legal cap, so enter your tub's listed standby watts for a closer figure.

Adjust it to your exact job

Your hot tub

Type

Fill volume

gal

On the spec sheet or the tub's California Energy Commission listing (filled to mid-skimmer).

Standby power

Title 20 caps how much a covered spa may draw just to stay hot. Many tubs test well under the cap.

Settings

Water temperature

°F

Location

Electricity rate

Where the tub is

Price per kWh

EIA's state average: total residential revenue ÷ kWh sold, so delivery and fixed monthly charges are spread over every kWh.

400-gallon hot tub costs

$40.27a month on average

2,656 kWh a year · January up to $59.06 · $1.32 a day

At 18.19¢/kWh — U.S. average, Jan–Aug 2026 (EIA).

Per year: $4832,656 kWh
Coldest month (Jan): $59.06air 36°F
Standby rating: 244Wat a 37°F water–air gap
Average draw: 303Win an average U.S. climate

Monthly cost outdoors in an average U.S. climate

Turn it down a notch

Yearly cost by water temperature
Water	Per year	vs 102°F
98°F	$441	−$41.96
100°F	$462	−$20.98
102°F	$483	—
104°F	$504	+$20.98

What this includes

Using the legal maximum

244 W is the most a 400-gallon hard-shell spa sold in California may draw in standby. Enter your tub's listed rating for a closer figure.

How to cut it

Keep the cover on and replace it once it's waterlogged or sagging — the cover is part of the tested rating.
Heat loss grows with the gap between water and air: each degree lower saves roughly the share shown in the table.
Most of the year's cost lands in the coldest months — an enclosed or indoor tub sees a smaller gap; switch Location to compare.

Energy budget

2,656 kWh 400-gallon hot tub — keeping it hot for a yearcovered standby at 102°F, 18.19¢/kWh$483

Estimated total$483

State

¢/kWh

kWh a year

Per year

Coldest month

Minnesota

16.44

3,441

$566

$74.47

Colorado

16.8

3,261

$548

$63.33

New York

29.26

3,002

$878

$107.95

Ohio

18.81

2,961

$557

$69.72

Washington

14.42

2,974

$429

$46.11

Texas

16.03

2,031

$326

$42.20

California

32.58

2,407

$784

$83.85

Arizona

15.36

2,023

$311

$39.70

Florida

15.32

1,703

$261

$30.57

How this was worked out

Prices: EIA average residential rates for Jan–Aug 2026. Outdoor temperatures: NOAA Climate Prediction Center population-weighted normals.

The full method, material data and tips are on the main hot tub cost calculator page.