Hot Tub Electricity Cost Calculator

What a hot tub costs to run

Most of what a hot tub adds to your electric bill isn’t the time you spend in it. It’s the hours it spends under its cover, holding a few hundred gallons at about 102 °F while the air around it is colder. So three things decide the bill: how well your tub holds heat, how cold it gets outside, and what you pay for electricity.

The best single number for the first one is the spa’s standby power. Since June 1, 2019, portable electric spas sold in California must be tested for it: the average electricity used to hold 102 °F water with the cover on, in 60 °F air. The result goes on a label, and certified models are listed in the California Energy Commission’s appliance database. Many manufacturers publish it on spec sheets too, so you can often find it even outside California.

California also caps it. For a standard spa holding V gallons, standby power can’t exceed 3.75 × V^(2/3) + 40 watts:

Approximate. At California's test conditions (102 °F water, 60 °F air) and 18¢/kWh.

These are maximums for new spas sold in California, on a mild 60 °F day. Many certified models test well below the limit. Older spas, tired covers and cold climates can use much more.

How the estimate works

1. Start from your spa’s tested standby watts. If you don’t know it, the calculator uses the California maximum for your size from the table above.
2. Adjust for your conditions. Heat loss scales with the water–air temperature gap, so standby is multiplied by (water temp − outdoor temp) ÷ 42.
3. Add jet-pump energy for your soaks, if you enter the pump’s watts.
4. Multiply by your electricity rate.

Why winter bills are higher

At the 60 °F test condition, 102 °F water is 42 degrees warmer than the air. On a 30 °F day the gap is 72 degrees, and heat leaks out faster in proportion. Here’s one spa with a labeled standby of 200 W, at 18¢/kWh:

• 60 °F average outdoors: about 146 kWh a month, roughly $26.
• 30 °F average outdoors: standby rises to about 343 W, which is about 250 kWh a month, roughly $45.

Then add the jets. Four 30-minute soaks a week with a jet pump drawing 1,500 W (an example figure; check your pump’s label) adds about 13 kWh a month, roughly $2. Standby dominates.

Your electricity rate matters as much as the tub

EIA projects the average US residential price at about 18¢ per kilowatt-hour for 2026, but state averages run from around 12¢ to more than 40¢. The same tub can cost three times as much to run in one state as in another.

To get your real rate, divide your bill’s total charges by the kWh used. That includes delivery fees and taxes, which a quoted “energy rate” often leaves out. If you’re on a time-of-use plan, ask your utility whether heating can be shifted to cheaper hours; many spas let you schedule heat and filter cycles.

Ways to spend less

• Look after the cover. Replace it if it’s become heavy with absorbed water or no longer seals around the edge. It’s usually the biggest efficiency factor you control.
• Block the wind. A fence, screen or hedge cuts heat loss from the cover and cabinet.
• Turn it down when you’re away for more than a few days, but never off in freezing weather.
• Keep the lid on. An uncovered tub loses heat quickly through evaporation.
• Keep the water balanced. Scale on the heater element makes it work harder. The hot tub chemical calculator sizes doses for small volumes, using the capacity from your manual or the hot tub volume calculator.

What this leaves out

• Cover-off time. An open hot tub loses heat fast through evaporation. Long, frequent soaks in cold weather raise real bills above this estimate.
• Filtration and electronics don’t scale with temperature the way heat loss does, so estimates far from the 60 °F test condition are less precise.
• Older or damaged spas. A waterlogged cover or failed insulation can multiply standby use. Your utility’s smart-meter data is the best check.