What this estimator works out
This estimator multiplies your monthly gas and electricity usage by the unit rates you pay, giving an estimated monthly energy cost before standing charges.
Standing charges are excluded deliberately. They are a fixed daily cost that does not change with usage, so leaving them out makes it easier to see the effect of using less — which is the question most people are actually asking.
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Default unit rates are the Ofgem price cap average for Great Britain, Direct Debit, 1 July to 30 September 2026, including VAT. The cap is reviewed quarterly — use the rate from your own bill where it differs.
Before you estimate
- Take unit rates from a recent bill or your online account, in pence per kilowatt-hour. Gas and electricity rates differ substantially.
- Use kilowatt-hours, not pounds, for usage. Your bill or smart meter display will show them.
- Remember that gas meters often record in cubic metres, which must be converted to kilowatt-hours — your bill shows the conversion.
- Use a representative month. Winter usage can be several times summer usage, particularly for gas.
You pay a standing charge for every day you are connected, regardless of whether you use anything. It covers network and metering costs. Because it is fixed, it cannot be reduced by using less energy — which is why excluding it here shows the part of the bill your behaviour can actually change.
How this calculator works
Usage multiplied by rate, converted from pence to pounds:
Electricity cost = kWh × unit rate in pence ÷ 100
Gas cost = kWh × unit rate in pence ÷ 100
Total = electricity + gas, before standing chargesTo reach a full bill estimate, add the standing charges: multiply each daily standing charge in pence by the number of days in the period and divide by 100. On many tariffs the two standing charges together add £20 to £30 a month.
Worked example: a typical month
Using the default figures — 250 kWh of electricity at 26.11p, and 800 kWh of gas at 7.33p:
- Electricity: 250 × 26.11p = £65.28
- Gas: 800 × 7.33p = £58.64
- Total before standing charges: £123.92
Add roughly £26 of standing charges and the bill lands near £150. Note the ratio: gas provides more than three times the energy for less than the electricity costs, because gas is far cheaper per kilowatt-hour. This is why heating decisions dominate energy bills, and why a heat pump's efficiency has to be several times that of a gas boiler before it saves money at current relative prices.
Common mistakes
- Entering pounds instead of kilowatt-hours. The usage fields expect energy units.
- Using cubic metres for gas without converting. One cubic metre is roughly 11 kWh; your bill shows the exact factor.
- Using a summer month to budget for the year. Winter gas usage can be several times higher.
- Forgetting standing charges when comparing tariffs. A low unit rate with a high standing charge can cost more overall.
- Comparing a direct debit amount with a bill. Direct debits are smoothed estimates, not actual usage.
Frequently asked questions
Where do I find my unit rates?
On your most recent bill, in your online account, or in the annual statement your supplier must send. They are quoted in pence per kilowatt-hour, separately for gas and electricity, alongside the daily standing charge. If you are on a variable tariff, they change when the price cap is reviewed.
How do I convert gas from cubic metres?
Multiply cubic metres by the calorific value and a volume correction factor, then divide by 3.6. In practice this works out at roughly 11 kilowatt-hours per cubic metre, and your bill shows the exact calculation it used. If your meter is an older imperial one measuring in hundreds of cubic feet, the conversion factor is different again.
Why does my direct debit not match this?
Direct debits are set to spread an estimated annual cost evenly across twelve months, so you overpay in summer and underpay in winter. Comparing a single month's estimated usage against a direct debit will rarely match. Compare against your annual statement instead, or against the actual charges for the period.
Is a fixed or variable tariff better?
It depends on where prices are heading, which nobody knows. A fixed tariff buys certainty and may cost more if prices fall; a variable tariff tracks the price cap and moves both ways. If a fixed deal is close to the current cap and you value predictability, it is a reasonable trade. Check exit fees before fixing.
Is what I enter stored?
No. Usage and rates are processed entirely in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — energy bill support, efficiency schemes and consumer guidance
- MoneyHelper — help with energy costs and managing bills
Sources are checked at publication and can change — how I choose and check references.