kWh cost calculator

Because the fixed charge is part of what you paid and none of what you used. It is a fixed number of dollars spread across a variable number of kilowatt-hours, so it lands on the blended figure as an extra per-unit amount that no rate on the sheet contains — 42¢ a day over 30 days is $12.60, and across 900 kWh that is another 1.4¢ on every single one. Spread the same $12.60 across 450 kWh instead and it becomes 2.8¢.

The costs the utility incurs whether you consume anything or not: the meter and reading it, the service drop, billing, and a share of the poles and wires between you and the substation. Regulators generally allow it precisely because those costs do not scale with consumption, which is also the argument against it — it is the part of the bill that conservation cannot touch, and it falls hardest on the smallest accounts.

Blended for what has happened, marginal for what you are deciding. Working out what last month's water heating cost is a question about a bill that already exists, so the blended figure is right. Working out whether a more efficient machine pays for itself is a question about kilowatt-hours you have not used yet, and those come off the top of the schedule at the marginal rate — which on a stepped tariff can be half as much again. Justifying a retrofit against a blended rate quietly understates it.

From your utility's interval data rather than from an estimate, because this is the field on the page most likely to be badly wrong. Most metering now records in fifteen- or thirty-minute intervals and most utilities will let you download it, and an hour of adding those up beats any amount of reasoning about when you think the dishwasher runs. If you cannot get the data, enter two versions of the split — the one you believe and a pessimistic one — and see whether the decision you are making survives both.

Almost always, and they reset with the billing period rather than the calendar month, which produces an effect people find hard to believe. Two households using exactly the same amount per day pay different average rates if one is billed on a 28-day cycle and the other on a 34-day one, because the longer period pushes more kilowatt-hours past the first ceiling and into the dearer block. That is also why comparing one month against another is only fair after dividing by the days.

Compare them per therm and then correct for what each appliance does with it, because a therm delivered is not a therm useful. At a blended 16.744¢ a kilowatt-hour, electricity costs $4.91 for the 29.307 kWh in a therm; a gas furnace at 90% AFUE turns a therm of gas into 0.9 of a therm of heat, resistance heating turns a therm of electricity into a full one, and a heat pump running at a seasonal coefficient of performance of 3 delivers three. Only the last of those three changes the answer, and it changes it a lot.

Because a demand charge is not a price per kilowatt-hour and cannot be turned into one. It is billed on the highest average power over a single fifteen- or thirty-minute interval in the whole period, so two customers with identical consumption pay different demand charges depending on whether their loads happened to coincide. Dividing it by the month's kilowatt-hours would produce a number that changes when nothing about the tariff did, and would hide the one action that actually reduces it, which is staggering large loads rather than using less of them.