How we calculate appliance running costs

Energy (kWh) = watts × hours × duty cycle ÷ 1,000

Cost = kWh × price per kWh

Watts is the power the appliance draws while running. Hours is how long it is switched on. The duty cycle is the share of that time it actually draws power (see below). Dividing by 1,000 turns watt-hours into kilowatt-hours (kWh), the unit on your bill.

For longer periods we multiply the daily figure. A month is 30.4 days (365 days ÷ 12, rounded) and a year is 365 days. Results are rounded to 2 decimal places.

A 1,500 W space heater running for 1 hour. A simple resistive heater set to run continuously draws full power the whole time, so the duty cycle is 1. Energy = 1,500 × 1 × 1 ÷ 1,000 = 1.5 kWh. Run it 8 hours a day and that is 12 kWh a day, 364.8 kWh a month (12 × 30.4) and 4,380 kWh a year (12 × 365).

A 150 W fridge running all day. A fridge is plugged in 24 hours a day, but its compressor switches on and off to hold the temperature. If it runs 35% of the time, the duty cycle is 0.35. Energy = 150 × 24 × 0.35 ÷ 1,000 = 1.26 kWh a day, 38.30 kWh a month and 459.90 kWh a year.

The calculators then multiply the kWh by the price for your country or state, or by a price you enter.

Appliances controlled by a thermostat or compressor, such as fridges, freezers, air conditioners and water heaters, cycle on and off. The duty cycle is the share of time the appliance actually draws power.

Our default duty cycles are typical values. Real duty cycles change with room temperature, insulation, thermostat setting and how often a door is opened, so treat them as a starting point.

The wattages on our pages are typical ranges from product labels and specifications. Your appliance may differ, so use the figure on its own rating label when you can.

United States: the U.S. Energy Information Administration (EIA) average residential price, by state and for the US, in cents per kWh. Monthly, with about a two-month lag.

Europe: Eurostat household prices (dataset nrg_pc_204) for the 2,500–4,999 kWh a year band, including all taxes and levies, in national currency, for around 40 countries. Twice a year: January–June and July–December.

United Kingdom: the Ofgem price cap Direct Debit average unit rate for Great Britain. Quarterly. Actual rates vary by region.

Canada: the Canada Energy Regulator's modelled residential price for each province and territory at 1,000 kWh a month, before sales taxes. The national figure is our population-weighted average.

Australia: the regulated default offers for 2026–27, turned into an all-in price per kWh (bill divided by assumed use, GST and supply charge included). The national figure is the average of four regions.

Pakistan: the NEPRA slab rate a household using about 250 units a month reaches, before tax, adjustments and fixed charges.

Other countries with an official tariff (for example India, New Zealand and South Africa): the regulator’s or state-owned utility’s published household tariff, or the official national average where one exists. Each country page says exactly what the figure covers, whether taxes are included and when we last checked it.

Other countries: where we have no official figure, you enter the price per kWh from your own bill.

Every price on the site shows its source and the period it covers. Full details and links are on our Data sources page.

When we cost a single appliance, we use the unit rate only. Standing charges and other fixed fees are paid whether or not you switch the appliance on, so they are not part of its running cost.

Some sources are averages, not unit rates. The EIA figure, for example, spreads typical fees and taxes across each kWh, so it can differ from the unit rate on your bill.

In Pakistan, India, Japan, South Korea and parts of the US, the price per kWh rises as a household uses more. Units are billed in slabs, each with its own rate.

On these tariffs, the honest cost of running one more appliance is the marginal rate: the price of the slab your household’s last units fall into. For example, if your home normally uses 150 kWh a month and the second slab covers 101–200 kWh, a fan that adds 30 kWh a month takes you to 180 kWh. All 30 of those extra kWh are billed at the second-slab rate, not at your average price.

The marginal rate is usually higher than your average price. Our bill analyzer helps you find your slab, and the calculators let you enter its rate.

Some tables show an approximate US dollar figure so readers can compare countries. We convert using the European Central Bank’s euro reference rates, or the national central bank’s official rate for currencies the ECB doesn’t publish (such as the Pakistani rupee). This column is for comparison only and does not change your result.

Our results are estimates. Real costs differ with your exact tariff, time-of-use rates, regional prices, the appliance’s age and settings, the weather, and standby power. National and state averages hide local differences. Official prices are published after the period they describe, so they can be a little behind what you pay today. Every price shows the period it covers.

For the most accurate answer, use the price per kWh and the wattage from your own bill and appliance label.

An automated job checks our sources for new data every week. If new data is malformed, the build fails and the site keeps the last verified data.

If a number looks wrong, email uzairxdev@gmail.com. We fix confirmed errors and change the page’s “Updated” date. We never change that date without a real change.