How BillDecoded Calculators Work

What our calculators do

BillDecoded tools perform arithmetic on the figures you enter. They do not connect to a supplier account, check your identity, decide whether you owe a debt or determine a legal entitlement. Results are estimates until reconciled with your dated bills and tariff terms.

• kWh cost: usage × pence per kWh ÷ 100, plus billed days × daily standing charge ÷ 100.
• Meter readings: closing minus opening; gas volumes are converted using your bill’s calorific value, the 1.02264 volume correction factor and, for hundreds of cubic feet, the 2.83 conversion.
• Direct debit: annual forecast ÷ 12 plus (debt + target buffer − credit) ÷ adjustment months, floored at zero. An optional period forecast replaces the annual average for seasonal estimates.
• Economy 7: day and night consumption priced separately, including separate standing charges for the two tariffs.
• Complaint timing: first complaint date plus 56 calendar days. Actual scheme acceptance is decided by the Energy Ombudsman.

Rates, dates and tax

Use the unit rate and standing charge on the bill covering the period you are checking. Enter rates including the tax applicable to that fuel and date; the tools do not add VAT again. Split a period when rates change. An annual estimate holds the entered rates constant for 365 days and does not predict future quarters.

Illustrative inputs are examples. Regional reference tables carry their own period and review date. A national price-cap headline uses assumed consumption and is not a maximum household bill.

Sources: GOV.UK gas conversion, Ofgem rates, Energy Ombudsman process.

Rounding and limitations

We keep intermediate calculations unrounded and display currency to two decimal places. A supplier may round individual lines or use more rate precision, giving small differences. A difference is a reason to request a breakdown; it does not prove the supplier made an error. Negative usage, missing inputs and invalid dates are rejected rather than silently converted to zero.

Testing, privacy and corrections

We test worked examples, zero use, invalid inputs, gas units, credit exceeding forecast costs, seasonal periods and date boundaries. Calculator inputs stay in your browser and are not included in analytics events. If you find an error, send a correction with the page, non-sensitive example inputs and expected result. Do not send an account number or unredacted bill. Our editorial policy describes sourcing and independence.