Hot Tub Cost Calculator
Estimate what it costs to heat and run a hot tub over a month and a year.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Estimate recurring electricity cost from the hot tub’s total daily kWh use and your utility rate. Use a meter reading or a product test/label where available; consumption varies with the spa, cover, weather and use, so the default 5 kWh/day is only a replaceable example. The separate fresh-fill estimate uses water volume, fill and target temperatures, and heater power; it excludes heat lost by the tub and plumbing.
Worked example
calculated with the default values below
Total hot tub electricity use per day 5 kWh/day · Electricity rate (USD/kWh) 0.17 USD/kWh · Water volume 350 gal · Fill-water temperature 50 °F · Target water temperature 102 °F · Heater input power 4,000 W · Heater efficiency (assumption) 98 % Estimated electricity per month 152.2 kWh · Estimated electricity per year 1,825 kWh · Estimated monthly cost 25.87 USD · Estimated yearly cost 310.25 USD · Fresh-fill heating electricity 45.39 kWh · Fresh-fill heating cost 7.72 USD · Fresh-fill heating time 11.3 h
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
EkWh = V × 8.34 × max(0, Ttarget − Tfill) ÷ 3412.142 ÷ (η ÷ 100) ; heating hours = EkWh ÷ (heater watts ÷ 1000) ; monthly cost = daily kWh × 30.44 × rate
- V
- water volume (US gallons)
- Ttarget
- target water temperature (°F)
- Tfill
- fill-water temperature (°F)
- η
- heater efficiency (%)
- rate
- electricity rate (USD/kWh)
Recurring cost uses the total daily consumption entered (including all spa equipment) × 30.44 days or 365 days × the rate. Daily use is user-measured or user-estimated, not predicted from ambient temperature or cover quality. Fresh-fill heat-up is an idealized water-only estimate; real heat loss and warm-up time may be higher.
Frequently asked questions
How should I estimate daily hot tub electricity use?
Enter total daily use for the whole spa, including heater, circulation, controls and other equipment. Prefer a meter reading or a published test value for your model. Energy varies by spa, cover, weather and use; the 5 kWh/day default is only a placeholder. Do not add pump energy again if it is already included in your daily total.
What does the fresh-fill heating estimate include?
It estimates the electricity to raise the entered water volume from fill temperature to target temperature using water’s specific heat, heater input power and the efficiency you enter. It does not include heat lost from the tub, pipes or during warm-up, so actual time and use can be higher.