The short answer
Use the consumption-related price charged for each kWh, in the currency and billing period you want to model. A monthly payment or fixed service charge is not a unit rate. Keep fixed charges separate for whole-tariff comparisons, and retain any time, tier or tax boundary with the entered price.
Use the price charged for each kWh
An appliance cost calculator needs your consumption-related electricity price per kWh. A monthly payment, account balance or fixed service charge is a different quantity.
Find the electricity tariff or detailed bill for the dates you want to model. Copy the unit, currency and any time or usage band beside the rate. For a UK bill, Ofgem distinguishes the unit rate from the standing charge. For a US bill, the supply price may be only one part of the consumption charge.
Separate variable prices from fixed fees
| Bill item | How to treat it |
|---|---|
| Electricity unit price in pence or cents/kWh | Convert to pounds, dollars or euros/kWh |
| Separate supply and delivery prices, each charged per kWh | Include the applicable components on a consistent basis |
| Standing charge or fixed monthly service fee | Keep separate from a single appliance’s energy cost |
| Total payment, arrears or account credit | Do not use as the kWh price |
| Peak, off-peak, seasonal or tiered prices | Match the price to the energy being modeled |
PSE&G’s bill FAQ distinguishes supply from delivery charges and identifies kWh as its electric usage unit. This is one utility’s explanation, not evidence that every US bill uses the same charges. Read the units on each component of your own tariff.
If an illustrative bill has 12 cents/kWh for supply and 8 cents/kWh for delivery, both applicable to the same consumption, the combined scenario price is 20 cents/kWh, entered as 0.20 with USD selected. Add neither a fixed fee nor an already bundled price again.
Convert pence and cents once
These are separate illustrative rates, not current national prices or exchange-rate conversions:
| Tariff wording | Currency | Price input | Cost of 365 kWh/year |
|---|---|---|---|
| 28 pence/kWh | GBP | 0.28 | £102.20 |
| 20 US cents/kWh | USD | 0.20 | $73.00 |
| 30 euro cents/kWh | EUR | 0.30 | €109.50 |
A printed £0.28 or $0.20 price is already in the major currency unit. Dividing it again understates the result. Selecting another currency changes the display; it does not convert the value. See pence and cents conversion for the 100-fold error.
Do not turn fixed fees into appliance savings
If two compatible fridges differ by 50 kWh/year at £0.28/kWh, the energy-cost difference is £14/year. An unchanged standing charge does not increase that saving.
Dividing the whole bill by billed kWh can give an average price that includes fixed fees. That average can help describe past spending, but it can overstate the saving from avoiding one additional kWh. Use the applicable consumption-related rate for that question.
For two complete household tariffs, include fixed fees and whole-home consumption in the tariff comparison. A fixed monthly fee can be modeled as its annual total divided by the selected 365 or 366 days; record that assumption.
Keep time, taxes and tiers explicit
Use a consistent tax basis. These tools apply the price as entered and do not add tax automatically. Do not add a levy twice if it is already included in the quoted rate.
A single price does not reproduce a tiered bill or several time windows. The time-of-use guide explains energy weighting. Where extra consumption crosses a tier or other billing rule, use the supplier’s applicable terms rather than assuming the last bill’s average remains valid.
Keep the tariff name and date with the result. Then calculate one appliance or build a household estimate using the same clearly stated price basis.