Find the usage and the billing period
Look for electricity consumption measured in kilowatt-hours, usually abbreviated kWh. Note the start and end dates too. A 35-day bill will not compare directly with a 28-day bill, even if your daily habits are similar.
For a fair first comparison, divide each period’s kWh by its number of days. A 420 kWh bill over 30 days equals 14 kWh per day. A 448 kWh bill over 32 days also equals 14 kWh per day.
Separate variable and fixed charges
Electricity bills can distinguish supply, delivery and other charges. The EIA explains that rates may apply to individual services, and that the supplier and delivery utility may differ. Look at which line items are priced per kWh and which are charged once per billing period.
Illustrative bill: supply costs 10¢/kWh, variable delivery costs 7¢/kWh and another usage charge costs 1¢/kWh. The combined variable rate is 18¢/kWh, or $0.18. A separate $12 monthly account fee does not disappear when you use an appliance less.
Why total bill divided by kWh can mislead
Suppose 500 kWh costs $90 in variable charges plus a $12 fixed fee. The total is $102. Dividing $102 by 500 gives $0.204/kWh: an average all-in bill cost, not the $0.18 price of an additional kWh in this example.
Both figures answer legitimate questions. Use the all-in average to summarize a bill. Use the relevant variable rate to estimate how an appliance changes that bill. Taxes, credits and tiered rates can make the calculation more involved; ask the utility to explain unclear items.
Handle time-of-use prices separately
If a device uses 2 kWh at $0.12 and another 3 kWh at $0.30, the daily cost is $0.24 + $0.90 = $1.14. The usage-weighted rate is $1.14 ÷ 5 = $0.228/kWh. A simple unweighted average of the two rates would give a different result.
Our calculator accepts a single rate. Run separate scenarios for each time band, or use a properly weighted rate for the consumption you expect. State averages are useful background, but your own current tariff is the better input.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.