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Free calculator

Use this calculator to

  • Estimate the electricity cost of a single load from watts, hours per day and days
  • Sense-check an estimated bill before you query it with your supplier
  • Model how cutting running hours changes the cost before altering shift patterns
  • Convert any wattage and usage pattern into kWh, pence and pounds

Electricity Bill Calculator

Calculate your electricity cost from power usage and tariff. Uses pence/kWh (UK) by default.

W
hr
days
p/kWh
Result
—

Formulas

  • Energy (kWh) = W × hours / 1000
  • Cost (pence) = kWh × tariff rate (p/kWh)
  • Cost (£) = cost (pence) / 100

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

A business electricity bill has more moving parts than the unit rate suggests. Wholesale energy, network charges (DUoS, TNUoS, BSUoS), policy levies (RO, FiT, CfD, CCL), supplier margin, broker commission and VAT all sit inside what looks like a single p/kWh number. When the supplier presents the figure on a single line, the only way to know whether the rate is competitive is to model it from the ground up.

Bill validation is the most common reason businesses come to Purely Energy. A 100,000 kWh per year mid-market site at 35 p/kWh is paying £35,000 in energy plus standing charges plus VAT, and a 2 p/kWh error (whether through misclassified VAT, an incorrect capacity band, or a non-commodity reconciliation that has not been applied) is £2,000 of overpayment per year. Multiply across a portfolio and the case for line-level scrutiny becomes obvious.

Purely Energy quotes are transparent by construction: wholesale, non-commodity costs, supplier margin and our own margin are shown separately on every offer, in the same units, on the same page, for every quoted site. If a current supplier or broker cannot do that, the bill calculator is the only way to reverse-engineer what you are actually paying for, and we will gladly run that exercise alongside a fresh tender so the comparison is structural rather than headline.

Common questions

How is an electricity bill calculated?

The energy line is consumption times price: kWh = watts x hours / 1000, multiplied by the number of days, then by your unit rate in pence per kWh. On top of that a real bill adds the standing charge (a fixed pence per day), and for business supplies the Climate Change Levy and VAT. This calculator gives you the energy line, which is the part your usage decisions actually control.

What is a standing charge and why is it not in this result?

The standing charge is a fixed daily fee that covers the cost of keeping your site connected: metering, network maintenance and supplier overheads. You pay it every day whether you use 1 kWh or 1,000 kWh, so it is independent of the appliance usage you model here. To include it, multiply your standing charge in pence per day by the number of days and add it to the calculated cost.

Where do I find my unit rate?

It is on your bill or contract as a pence per kWh figure, sometimes labelled the unit price or unit charge. Business contracts often carry more than one rate: day and night rates on a two-register meter, or peak, off-peak and weekend bands on half-hourly supplies. If you have multiple rates, run the calculator once per band using the hours that fall in each, then add the results.

Why does my actual bill not match the calculator?

A bill covers every load on the meter, not one appliance, and includes the standing charge, levies and VAT. Appliances with thermostats also cycle, so they draw less than their plate rating on average. Estimated meter readings cause a further gap: the supplier bills a forecast, then corrects when an actual read arrives. Use the calculator for the marginal cost of a specific load, and reconcile whole bills against actual meter readings.

Do businesses pay VAT and the Climate Change Levy on electricity?

Most business supplies are charged VAT at the standard 20 per cent rate plus the Climate Change Levy, which is a per-kWh government charge. Sites with low usage, averaging 33 kWh a day or less of electricity, qualify for the reduced 5 per cent VAT rate and CCL exclusion under the de minimis rules, as do certain charities and domestic-use cases. Neither is included in this calculator's result, so add them when estimating a full bill.

Related calculators

The conversions that procurement and engineering use alongside this one.

Electricity Bill Calculator | Purely Energy