How to Find Your Electricity Rate for a Cost Calculator
For a device-cost estimate, use the charges that change when you use another kilowatt-hour. Your total bill divided by usage can include costs that will remain even if you turn the device off.
Read the units beside each charge
Find the bill’s energy usage in kWh, then identify the line items priced per kWh. Depending on the utility, these may include supply, delivery, fuel, or other adjustments. A rider or adjustment can be either fixed or usage-based: its name alone does not tell you.
Keep fixed account charges separate. Duke Energy’s billing explanation, for example, distinguishes a fixed customer charge from usage-based charges and riders. Your own tariff determines which charges apply.
A sample bill, with the math shown
| Charge | Calculation | Amount |
|---|---|---|
| Energy | 800 × $0.11 | $88 |
| Delivery | 800 × $0.05 | $40 |
| Usage adjustment | 800 × $0.01 | $8 |
| Fixed fee | Per month | $15 |
| Total | All charges | $151 |
The variable total is $136. Divide $136 by 800 kWh to get $0.17/kWh, or 17¢/kWh.
Dividing the entire $151 bill by 800 gives 18.875¢/kWh. That is an average including the fixed fee. Using it to predict savings from unplugging a device would allocate some of that unchanged fee to the device.
At the variable 17¢ rate, a constant 100 W load uses 876 kWh and costs $148.92 a year.
When one rate is not enough
- Time-of-use prices: match the energy used to each price period. See the worked time-of-use example.
- Usage tiers: estimate which tier the added or avoided kWh falls into. A large change may cross a threshold.
- Demand charges: a charge based on peak kW cannot generally be estimated by multiplying kWh by one rate.
- Taxes, credits, and minimum bills: check how your tariff applies them. Do not assume every dollar on the bill varies with device usage.
Enter the rate correctly
Our calculator asks for cents per kWh. Enter 17 for $0.17/kWh. The default 18¢ is only an example. Keep the billing period and tariff with your notes, and update your estimate if the price changes.
If the bill’s categories are unclear, ask the utility which charges change when consumption rises by 1 kWh. A simple device estimate is useful, but it is not a complete recreation of every billing rule.
Sources and calculation notes
Worked examples are Always On Cost calculations using the stated assumptions, not product tests or utility quotes. Unless noted otherwise, estimates use a fixed rate and repeating daily schedule, with 365 days per year. USD amounts are rounded for display.