Electricity Cost Calculator

How the kWh Formula Works

Every electricity bill in every country comes down to the same arithmetic. The formula is short, transparent, and worth memorising:

Cost = (Watts × Hours ÷ 1,000) × Rate per kWh

Run a 1,000-watt heater for one hour and you have used 1 kilowatt-hour (kWh). Run a 100-watt LED bulb for ten hours: also 1 kWh. The dividing-by-1,000 step is there because your supplier bills in kilowatts, not watts.

A worked sketch. A 2,000W kettle boiled for 5 minutes. Hours = 5 / 60, which is roughly 0.083. Energy = (2,000 × 0.083) / 1,000 = 0.167 kWh. At the current April-June 2026 Ofgem cap rate of 24.67p per kWh, that is about 4p per boil. Boil it five times a day for a year and you spend roughly £75 on hot water for tea and coffee.

This calculator does the same arithmetic in any of four currencies. Accuracy comes from honest inputs: the actual wattage on the appliance label, the hours you really use it, and the rate from your most recent bill, not the headline figure on a comparison site.

What kWh, kW, MWh and Watts Actually Mean

These four units cause more confusion than any other corner of an energy bill, so it is worth slowing down for a paragraph.

A watt (W) measures power, the rate at which an appliance pulls electricity right now. It does not include time. An LED bulb is rated 10W; a hairdryer is rated 2,200W; a fridge averages 100-200W while running.

A watt-hour (Wh) measures energy, how much power was used over how long. A 100W bulb running for one hour uses 100 Wh.

A kilowatt (kW) is simply 1,000 watts. A 2.5kW kettle is the same as a 2,500W kettle. Manufacturers use whichever number makes the marketing copy easier.

A kilowatt-hour (kWh) is 1,000 watt-hours. This is the unit your meter records and your bill charges. One kWh equals a 1,000W appliance running for one hour, or any equivalent combination.

A megawatt-hour (MWh) is 1,000 kWh. You will see MWh in solar export contracts, EV fleet billing, and commercial supply tariffs, but rarely on a household bill. In short: watts are speed of use, kWh is total use, and money follows.

Peak vs Off-Peak: When Timing Changes the Price

Most households are on a single-rate tariff: every kWh costs the same regardless of when you use it. But time-of-use tariffs are quietly becoming more common as smart meters spread.

In the UK, the classic example is Economy 7: roughly seven hours overnight (commonly midnight to 7am) sit at 10-12p per kWh while daytime rates can reach 30-35p. Octopus Agile and similar half-hourly tariffs swing further, with rates updating every 30 minutes against wholesale prices.

In the United States, time-of-use plans are common in California, Arizona, and parts of the Northeast, with peak afternoon rates often 2x to 3x the off-peak overnight rate. Australia has comparable tariffs through most distributors. In Canada, eligible Ontario customers can choose between time-of-use, ultra-low overnight, and tiered price plans through the regulator's structure; the best plan depends on the household's usage pattern, so check your current plan and enter the actual rate from your bill rather than assuming a TOU default.

If your tariff has these bands, the single rate field above is a starting point, not a final answer. Run the calculator twice, once for peak and once for off-peak, then weight the result by how many hours fall in each band.

Common Appliance Running Costs

What this means for you: Heating is by far the biggest energy cost. A single electric heater can cost more than your fridge, TV, laptop, and all your lights combined. If you use electric heating, look at heat pumps and insulation upgrades before chasing small standby savings elsewhere.

Worked Example: Priya’s Winter Heating Bill

Priya rents a one-bedroom apartment in Toronto. The building radiator is weak, so most evenings she runs a 1,500W oil-filled portable heater for four hours, from 6pm to 10pm. Her supplier charges 19¢ CAD per kWh.

Daily energy = (1,500 × 4) / 1,000 = 6 kWh.
Daily cost = 6 × $0.19 = $1.14.
30-day monthly cost = $34.20.
Across a 5-month Toronto winter (about 150 evenings) = roughly $171.

When Priya plugged the same numbers into this calculator, the figure surprised her. So she experimented. She switched to a 50W heated throw blanket while watching TV, kept the central heating set 2°C lower, and ran the portable heater for only the first 30 minutes after coming home cold.

New routine: 1,500W heater for 0.5 hours plus 50W throw for 4 hours.
Daily kWh = (1,500 × 0.5 + 50 × 4) / 1,000 = 0.95 kWh.
Daily cost = 0.95 × $0.19 = $0.18.
Across the same 150 winter evenings = $27.

Saving across one winter: about $144, with no perceived loss in comfort. The lesson is not that heaters are evil; it is that pairing the right wattage to the actual job you need it for is where most of the saving lives.

UK Energy Price Cap Timeline

What this means for you: The April-June 2026 cap eased back from the January-March quarter, but rates remain higher than pre-2021 levels. The figures shown are typical Direct Debit averages for England, Scotland and Wales (including VAT). The October to December 2026 cap has not been announced yet; Ofgem confirms a publication date of 26 August 2026. The cap is a maximum unit rate, not a guaranteed bill total; your actual rate may differ depending on tariff, region, payment method and meter type.

Average Electricity Rates Around the World

Pricing varies sharply by country and even by region inside one country. The figures below are residential averages for context. Your tariff may be very different.

United Kingdom. The Ofgem price cap for 1 April to 30 June 2026 sets the typical Direct Debit electricity rate at 24.67p per kWh in England, Scotland and Wales, plus a 57.21p daily standing charge (figures include VAT). Northern Ireland is regulated separately by the Utility Regulator. Caps update quarterly, so always check the live figure for the period you are budgeting for.

United States. Residential rates vary strongly by state and utility, so a single national average is only a rough guide. Hydro-rich states such as Idaho and Washington tend to sit toward the lower end; Louisiana sits there too thanks to abundant natural gas. New England states typically sit higher, California utilities often higher still, and Hawaii is the standing outlier (well above 40¢ per kWh in many tariffs) because almost all generation fuel is imported. Always check the unit rate on your most recent bill rather than relying on a national figure.

Canada. Rates vary by province and local utility, and the spread is wide. Hydro-heavy provinces such as Quebec and Manitoba sit toward the bottom of the range. Atlantic provinces such as Nova Scotia and Prince Edward Island sit higher up the mainland range, and northern territories sit higher still because of remote-grid economics. Ontario customers can choose between time-of-use, ultra-low overnight, and tiered plans depending on their habits, so the right "Ontario rate" depends on the plan you pick. Treat any single Canadian average as a starting point only.

Australia. Rates vary by state, distributor, retailer and tariff type. Among advanced economies they sit toward the higher end overall, with South Australia often at the top of retail tariffs and Western Australia generally the cheapest mainland state. The Australian Energy Regulator's Default Market Offer is a safety-net standing-offer reference price for specific regions, not a national per-kWh average, so do not treat it as a typical bill rate. Many distributors offer solar-friendly export tariffs and time-of-use is increasingly common for new connections. The currency selector at the top of this tool prefills typical residential ballpark figures, but stays editable so you can paste in the exact rate from your bill.

Quick Wins to Cut Electricity Costs

Common Mistakes When Estimating Electricity Cost

A few errors come up every time people try to estimate appliance cost without a calculator like this one.

Confusing watts with watt-hours. A 2,400W appliance does not cost 2,400p per hour. The watts get divided by 1,000 first, so 2.4 kW × your rate per kWh equals the cost per hour.

Forgetting the standing charge. Your unit rate is only half the bill. UK households pay roughly £180-£240 a year in daily standing charges before consuming a single kWh. Many US utilities charge equivalents called fixed or customer charges. Calculators like this one show consumption cost only.

Reading the manufacturer’s peak rating literally. A 2kW washing machine is rated for its peak draw, mostly during the heater phase. Across a full cycle the average pull is far lower, often 0.7-1.1 kWh per wash, not 2 kWh.

Treating heating as constant. A thermostatic heater pulls full wattage to warm the room, then idles. Real-world energy use is typically 50-70% of the rated wattage averaged over the hour, not 100%.

Ignoring tariff bands. If you are on Economy 7 or any time-of-use plan, a single average rate hides serious savings or extra costs. Run the numbers for each band separately and weight them by usage hours.

Where This Calculator’s Estimate Has Limits

This tool gives you a clean unit-cost estimate, useful as a starting point but not the whole bill. Three caveats worth keeping in mind.

The rates prefilled by the currency selector are residential averages broadly in line with regulator guidance and typical public tariff examples in each country. Real-world rates vary widely by tariff, region, retailer, payment method and contract date; assume your actual rate can differ by 10-30% in either direction, and use the rate field to override with the figure on your most recent bill.

The calculator assumes a constant wattage. In reality, fridges cycle on and off, washing machines vary draw by phase, and inverter air conditioners adjust continuously. For variable-load appliances, the manufacturer’s annual energy figure on the EU energy label or the US EnergyGuide label is more accurate than wattage times hours.

Standing charges, supplier service fees, demand charges (in some US states), and renewable levies are excluded. This tool reports unit cost; for a full monthly bill estimate, add the standing or fixed charge from your supplier on top.

Late-Night, Shift-Work, and Off-Peak Routines

Many households shift their highest-energy activities, cooking, dishwashing, laundry, into the late evening or early morning. Some have seasonal late-night routines too, such as cooking or laundry during Ramadan, exam periods, shift-work weeks, or hot summer evenings when the kitchen is cooler.

If you are on a single-rate tariff, the timing does not change the cost. But if you are on Economy 7, Octopus Agile, an Ontario time-of-use plan, or any US TOU tariff, the same dishwasher cycle can cost 50-70% less between midnight and 7am than it does at 6pm. Worth a quick check of your current tariff: a switch to time-of-use can pay back in months for households that already cook and clean late.

Related Tools