Electricity Cost Calculator — Free Online Calculator
Calculate how much it costs to run any appliance. Enter watts, hours of use, and your electricity rate to find daily, monthly, and yearly costs.
How to Use This Calculator
Enter the appliance wattage (check the label or manual), how many hours per day you use it, and your electricity rate in dollars per kilowatt-hour (check your utility bill). The calculator shows your daily, monthly, and annual running costs.
The Formula Explained
Energy cost = (Watts × Hours) / 1000 × Rate. First, convert watt-hours to kilowatt-hours by dividing by 1000. Then multiply by your electricity rate. For example, a 1500W space heater running 8 hours at $0.15/kWh costs: (1500 × 8) / 1000 × $0.15 = $1.80 per day, or $54 per month.
Common Appliance Running Costs (8 hrs/day, $0.15/kWh)
| Appliance | Watts | Daily Cost | Monthly Cost |
|---|---|---|---|
| LED Bulb | 10W | $0.01 | $0.36 |
| Laptop | 65W | $0.08 | $2.34 |
| Refrigerator | 150W | $0.18 | $5.40 |
| TV (55") | 120W | $0.14 | $4.32 |
| Space Heater | 1500W | $1.80 | $54.00 |
| Window AC | 1200W | $1.44 | $43.20 |
| Clothes Dryer | 5000W | $6.00 | $180.00 |
| EV Charger (L2) | 7200W | $8.64 | $259.20 |
Understanding Electricity Cost Math
Electricity cost calculation sits at the intersection of simple arithmetic and economic decision-making. The math is trivial: power times time equals energy, energy times rate equals cost. Doing it accurately for dozens of devices and projecting annual costs reveals surprises most people miss when they think about their bill. The refrigerator you never consider costs more than the TV you obsess over. The always-on devices add up to more than the big appliances you deliberately use. And the small efficiency gaps compound across years into significant money.
The master formula: Annual cost in dollars = watts × hours per day × 365 × rate per kWh / 1000. Every other calculation reduces to this one. For a device with varying duty cycle (AC, refrigerator), use average power draw instead of nameplate watts. For devices with seasonal use (heaters, AC), calculate seasonal cost separately and add. For time-of-use rates, split daily hours into peak and off-peak portions with different rates. The formula extends to cover all the real-world complexity.
Worked Example: Electric Vehicle Charging
A Tesla Model 3 with 75 kWh battery, 300 miles of range. Electricity consumption: 75 / 300 = 0.25 kWh per mile (4 miles per kWh). Driving 12,000 miles per year: 12,000 × 0.25 = 3,000 kWh per year of charging.
Cost at home (16 cents per kWh): 3,000 × 0.16 = 480 USD per year, or 4 cents per mile. Cost on DC fast charging (40 cents per kWh): 3,000 × 0.40 = 1,200 USD per year, or 10 cents per mile. Mixed home/DCFC at 80/20 split: 3,000 × (0.80 × 0.16 + 0.20 × 0.40) = 624 USD per year.
Compare to gasoline: same 12,000 miles at 30 mpg = 400 gallons. At 3.50 USD per gallon: 1,400 USD per year, or 11.7 cents per mile. EV home charging is about 66% cheaper per mile than gasoline at these rates. The annual fuel savings of 920 USD (home charging) helps offset the EV purchase premium over 8-10 years.
Worked Example: Pool Pump Running Cost
A typical residential pool pump: 1.5 HP motor drawing about 1,800W when running. Recommended runtime: 8 hours per day in summer, 4 hours per day in winter. Average 6 hours per day year-round.
Daily energy: 1,800 × 6 / 1000 = 10.8 kWh. Monthly: 324 kWh. Annual: 3,942 kWh. Annual cost at 16 cents: 630 USD. That is before any filter backwashing, pool heater, or pool cleaner loads.
Variable-speed pool pump alternative: same duty pumping done at lower speeds (500-800W average instead of 1,800W). Annual consumption drops to about 2,000 kWh, or 320 USD per year. Savings 310 USD per year. Variable-speed pump costs about 1,000-1,500 USD more than a standard pump. Payback: 3-5 years. Utility rebates (common in pool-heavy states like California and Florida) can cut the effective cost by 300-500 USD.
For pool owners, the pump is often the single biggest controllable electrical load in the home. Optimizing pump runtime and upgrading to variable-speed consistently produces some of the best ROI in residential energy efficiency.
Five Cost Calculation Mistakes
1. Using wrong rate (tier vs average). For tiered rates, marginal cost of additional usage is higher than the average rate on your bill. Efficiency investments should use marginal rate, not average.
2. Forgetting peak demand charges. On commercial time-of-use or demand-based tariffs, the cost of running a device depends on WHEN you run it, not just how long. Cost calculations must include rate schedule timing.
3. Ignoring taxes and fees. The "rate" on your bill often excludes taxes (6-10% additional) and franchise fees. Real effective rate is 10-20% higher than the stated "per kWh" figure.
4. Using old rates in projections. Utility rates rise 3-5% per year on average. A 10-year savings projection at today's rate understates actual savings by 30%+.
5. Forgetting seasonal variation. Many utilities charge higher summer rates. Calculating annual cost using winter rate under-estimates total cost.
Typical Device Running Costs
At 16 cents per kWh, running continuously for 1 year:
5W LED bulb: 7 USD. 10W device (router, smart speaker): 14 USD. 50W device (TV on): 70 USD. 100W device (old light, desktop): 140 USD. 500W device (small heater, computer): 700 USD. 1000W device (microwave running, toaster): 1,400 USD. 1500W (space heater continuous): 2,102 USD. 3000W (EV charger at 30A continuous): 4,205 USD.
Seasonal and cycling devices (not continuous):
Refrigerator (modern): 60-90 USD per year. Water heater (electric, family of 4): 600-800 USD per year. Central AC (3-ton, Southern summer): 300-500 USD per season. Electric dryer: 80-120 USD per year. Dishwasher: 40-70 USD per year.
The big takeaway: the devices that cost the most are usually the ones you never notice, not the ones you deliberately turn on. HVAC and water heating dominate most residential bills. Next round of efficiency investments should target these categories.
Rates and Billing Standards
US electricity rates are published monthly by the US Energy Information Administration (EIA) at eia.gov. State-level averages are updated monthly for residential, commercial, and industrial customer classes. Utility-specific rates are available from state public utility commission filings.
For TOU and demand-based rates, check your specific utility's rate schedule document (usually labeled "Schedule R-1", "RS-TOU", etc.). These documents define every charge component, when peak and off-peak periods apply, and how demand charges are calculated. Understanding your rate schedule is the first step in any serious energy cost analysis — national averages are useful for broad comparisons but your specific bill depends on your specific tariff.
Electricity cost: how to read your bill and what the math actually means
The electricity-cost math is simple: kWh consumed times the rate per kWh. Where it gets complicated is what counts as "the rate." A typical residential bill has fixed customer charges, energy charges (the per-kWh part), delivery charges, and a small zoo of riders, surcharges, and state fees. The calculator gives the marginal cost of running a specific appliance, which is what matters for energy decisions; the total bill includes fixed components that do not change with usage.
The formula and what it does
Watts and hours give watt-hours. Divide by 1000 for kWh. Multiply by your per-kWh rate. The rate you use should be the marginal rate, which is the rate you actually pay for additional usage. On tiered rate plans (CA, NY) this is the tier you are currently in. On TOU plans, it depends on time of use.
Worked example
Scenario: 1500 W space heater run 8 hours/day for 30 days. Find monthly cost in different states.
Monthly kWh: 1500 W x 8 hr x 30 d / 1000 = 360 kWh. Cost: 360 x rate. Texas at 14.3 cents: $51.48. US average 16.4 cents: $59.04. California at 30.8 cents: 10.88. Hawaii at 41.2 cents: 48.32. The same heater triples in operating cost across states. This is why heat pumps make sense everywhere; their 3x efficiency advantage knocks operating cost back below resistance heat in Texas, and to about a third of resistance cost in California.
US residential electricity rates (April 2026, top + bottom states)
| State | Avg rate (c/kWh) | Monthly bill, 900 kWh |
|---|---|---|
| Hawaii | 41.2 | $371 |
| California | 30.8 | $277 |
| Massachusetts | 29.4 | $265 |
| Connecticut | 28.6 | $257 |
| New York | 23.1 | $208 |
| US average | 16.4 | 48 |
| Texas | 14.3 | 29 |
| Florida | 13.7 | 23 |
| Washington | 11.2 | 01 |
| Idaho | 10.6 | $95 |
| North Dakota | 10.4 | $94 |
Source: US Energy Information Administration (EIA) Electric Power Monthly, April 2026 release. Rates are residential class average including delivery and supply charges.
Common mistakes to avoid
Using average rate instead of marginal. Bill total divided by kWh gives blended rate, which is misleading for decision-making. Tiered plans charge higher rates above thresholds; you want the rate you would pay for the next kWh consumed.
Ignoring delivery and supply separately. In deregulated markets (TX, PA, NY, IL), delivery is fixed with the utility while supply is competitive. Switching suppliers only affects the supply portion.
Forgetting demand charges. Residential bills rarely have these; small commercial accounts often do. A 5 kW peak demand at 0/kW adds $50/month independent of kWh.
Frequently asked questions
How do I find my actual marginal rate?
Pull a recent bill. Find the energy charge (cents per kWh). Add the delivery charge per kWh (sometimes called distribution). Add any line-item per-kWh riders. Ignore the fixed customer charge. That sum is your marginal rate.
What is a TOU rate?
Time-of-use. Different rates for different hours: peak (afternoon/evening, expensive), off-peak (overnight, cheap), shoulder. Common in CA, NY, AZ. Can swing 3x between off-peak and peak. Saves money if you shift heavy loads (EV, dishwasher, dryer) to off-peak.
Why is my bill higher in summer or winter?
HVAC. A central AC pulls 3-5 kW continuously when running. In a hot Texas summer at 200+ hours of run time per month, that adds 600-1000 kWh ($80-150). Same scale in cold-climate winter heating, especially electric resistance.
What are the cheapest hours to run laundry?
On flat rate: any hour, same cost. On TOU: typically 9 PM to 6 AM weekdays or all weekend. Check your specific tariff; off-peak hours vary by utility.
Are smart meters reading my usage accurately?
Yes, AMI (advanced metering infrastructure) meters are accurate to about 0.5 percent per ANSI C12 standards. Old electromechanical meters drifted slightly with age but were also accurate when new.
Why does my neighbor pay less per kWh?
Different rate plan, different supplier (in deregulated markets), or different tariff schedule. Check whether your account is on the optimal plan for your usage pattern; utilities usually do not auto-switch you.
What is the cheapest state for electricity?
North Dakota and Idaho at around 10.4-10.6 cents/kWh average per EIA April 2026 data. Hawaii is most expensive at 41.2 cents, driven by oil-fired generation and shipping costs.