UK Energy Bill Calculators
This hub is for calculation-led intent. Pick the calculator that matches the number you are trying to challenge: direct debit, usage cost, standing charge, bill from readings or price cap rates.
Choose the right calculator
Direct debit check
Sense-check whether your supplier’s proposed monthly payment is reasonable.
Open calculatorChallenge templatekWh and bill cost
Turn kWh, p/kWh and standing charges into an estimated bill subtotal.
kWh calculatorBill from readingsRates and standing charges
Use the right region, payment method and standing charge before challenging a bill.
Regional ratesStanding charge calculatorBill crosses a rate change
Split electricity, gas and standing charges by their actual dates and kWh.
Open split-period calculatorCalculator plus action
| If your result suggests | Do this next | Relevant page |
|---|---|---|
| Direct debit looks too high | Ask for forecast, balance, buffer and review period | /direct-debit-increase-complaint-template/ |
| kWh subtotal does not match bill | Check rates, dates, VAT and standing charge | /energy-bill-dispute/ |
| Standing charge dominates a low-usage bill | Confirm daily rate and days billed | /standing-charge-too-high-uk/ |
| Meter reading bill seems wrong | Send reading evidence and ask for rebill | /wrong-meter-reading-complaint-template/ |
Annual energy bill estimator
Enter your yearly kWh from an annual statement or your bills. The defaults use Ofgem’s revised 2026 medium values: 2,500 kWh electricity and 9,500 kWh gas. The selectable rates are dated July–September 2026 examples. Replace them with your own tariff; a full year at those rates is an illustration, not a future price forecast.
Default kWh reflects Ofgem’s medium-use benchmark from 1 July 2026. Regional rates shown are dated July–September 2026 examples. Rounded national rates give £1,663.84 for this input, while Ofgem publishes a £1,663 headline; region weighting and rounding differ. Use your actual bill rates for a personal check.
Check my direct debitStanding charges: £314.74. Estimate assumes the dated rates for 365 days; no future price changes are forecast.
Rates shown default to the Ofgem cap for 1 July to 30 September 2026, direct debit, including VAT. This is a sense-check, not a quote, and it does not model time-of-use tariffs.
The formula, and the four things people get wrong
cost = ( units × unit rate ÷ 100 ) + ( days × standing charge ÷ 100 )
| Mistake | What happens | Fix |
|---|---|---|
| Forgetting the standing charge | Your figure is £26 a month under on dual fuel. | Always add days × p/day. |
| Using the headline cap figure as a rate | A price-cap headline is an annualised typical-use illustration, not a rate. Nothing works if you multiply by it. | Use p/kWh from your bill. |
| Counting days wrong | Off by a few pounds, and it hides genuine double-billed days. | Use the supplier’s billed days and check that consecutive periods do not overlap. |
| VAT confusion | Wrong tax treatment changes the total. | Ofgem's published rates include applicable VAT. Use rates including tax here; check the fuel and period before adding tax separately. |
Gas has one extra step
Gas meters measure volume, not energy. If your meter reads in cubic metres, the bill converts it:
kWh = m³ × 1.02264 × calorific value ÷ 3.6
The calorific value is printed on your bill and is typically around 39–40. The volume correction factor 1.02264 is standard. An imperial meter reading in hundreds of cubic feet is multiplied by 2.83 first to get cubic metres. In practice: use the kWh figure the bill has already calculated, and only do this arithmetic if you are checking whether the conversion itself is right.
Which calculator answers which question
| Your question | Use | What you need to hand |
|---|---|---|
| “Is my monthly payment fair?” | Direct debit calculator | Annual forecast, account balance, any debt, the supplier's proposed amount |
| “What does this much energy cost?” | kWh to cost calculator | kWh used, unit rate from your bill |
| “Is this bill right for these readings?” | Bill from meter reading | Opening and closing readings, unit rate, days billed |
| “Why am I charged when I use nothing?” | Standing charge calculator | p/day from the bill, days in the period |
| “What should a year cost me?” | The estimator above | Annual kWh, your region |
A calculator result is a sense-check, not proof. If your figure and the bill differ by more than a pound or two, that is the start of a question — ask the supplier for their calculation in writing. It is not, on its own, evidence that the bill is wrong: the difference is often a rate change mid-period, or VAT handled differently.
What to do with the answer
The numbers roughly agree
The bill is arithmetically right. If it still feels too high, the question is about usage, not billing — start at why the bill is high.
The numbers differ by a few pounds
Usually a rate change mid-period or VAT. Ask for the calculation showing how the days split between rate periods.
The numbers differ a lot
Check the readings on the bill against your meter first. A wrong reading explains far more large discrepancies than a pricing error does. More
You cannot find the rates
They are in the detailed charges section of the bill, not the summary. If you genuinely cannot find them, ask — a supplier must be able to tell you the rates applied to your account.
Frequently asked questions
Which calculator should I use first?
Start with the problem: direct debit amount, kWh cost, standing charge, meter reading or price cap rate.
Can a calculator prove the supplier is wrong?
No. It creates a sense-check and helps you ask for the right breakdown.
Should I use national average rates?
Use your bill or official regional rates whenever possible.
What should my annual energy bill be?
Use your own kWh and current tariff for a useful estimate. At July–September 2026 national average rates, the revised Ofgem medium-use inputs of 2,500 kWh electricity and 9,500 kWh gas produce £1,663.84 from rounded rates over 365 days. Ofgem’s published headline is £1,663; a bill for your household can differ.
Do these calculators include VAT?
The July–September 2026 example rates above include the applicable 5% VAT. Great Britain domestic electricity VAT becomes 0% from 1 October 2026 to 31 March 2027; gas remains at 5%. If you enter rates from your own bill, check whether that bill quotes them including or excluding VAT — getting this wrong puts your answer out by exactly 5%.
Why does my bill not match the calculator?
The two usual reasons are a rate change part-way through the billing period, which splits the days across two rates, and VAT being handled differently. A difference of more than a few pounds is worth asking about; check the readings first.
Official sources used for this page
BillDecoded translates official process and billing information into practical checks. It is not affiliated with the Ombudsman, Ofgem, Citizens Advice, Which? or any supplier.