Electricity Bill Calculator (from Usage & Unit Price)

Finding the numbers on your bill

Every bill is built from the same few pieces, even if the names differ by country and provider. Usage is the difference between the current and previous meter readings, in kWh. The energy rate is the price per kWh; many bills split it into a supply or generation charge and a delivery or distribution charge, and you should add those together and enter the sum as the unit price. The base charge (also called a standing, customer or service charge) is the fixed amount you pay regardless of usage; if it is quoted per day, multiply it by the number of days in the billing period.

Any other per-kWh surcharge, such as a renewable-energy levy or a fuel or power-cost adjustment, can go in the levy field, or you can enter 0 there. Taxes are not added, so compare the result with the pre-tax subtotal on your bill.

A worked example

Suppose a household used 750 kWh at 0.16 per kWh, with a base charge of 15 and no levy. The energy charge is 750 × 0.16 = 120, and the total is 15 + 120 = 135. The effective unit price is 135 ÷ 750 = 0.18 per kWh. Note that the calculator rounds the total down to a whole currency unit, so for amounts that include cents treat the result as an estimate.

Estimating what one appliance costs

Energy in kWh equals power in watts × hours of use ÷ 1,000. A 1,500 W space heater run 4 hours a day uses 6 kWh a day, or 180 kWh over 30 days; at 0.16 per kWh that adds 28.80 to the month. A device drawing 5 W on standby around the clock uses 5 × 24 × 365 ÷ 1,000 = 43.8 kWh a year. If an appliance label lists annual consumption, such as 400 kWh per year, divide by 12 to get about 33.3 kWh per month.

When you estimate savings from using an appliance less, multiply the kWh saved by the per-kWh rate plus any per-kWh surcharges, not by the effective unit price. The effective price includes the base charge, which does not shrink when you use less, so it overstates the savings.

Tiered and time-of-use tariffs

This calculator takes a single unit price, but you can still model tiered or time-of-use pricing by entering a weighted average. With a hypothetical tariff of 0.14 for the first 500 kWh and 0.19 above that, 750 kWh costs 500 × 0.14 + 250 × 0.19 = 117.50, so enter 117.50 ÷ 750 ≈ 0.1567 as the rate. For time-of-use plans, weight each rate by its share of usage: 40 percent at a peak rate of 0.30 and 60 percent at an off-peak rate of 0.12 averages 0.192 per kWh.

The same trick shows how much a change in habits matters. Moving more usage into cheaper hours lowers the blended rate, and you can compare plans by keeping usage fixed and looking only at the total.