Calculation methodology
Nothing here is a black box. These are the exact formulas behind every result on the site.
Annual cost of a fuel
Annual cost = (usage in kWh × unit rate in pence ÷ 100) + (standing charge in pence × 365 ÷ 100). Monthly cost is the annual figure divided by twelve; we do not model seasonal billing patterns.
Break-even usage between two tariffs
Break-even kWh = (difference in daily standing charge × 365) ÷ (difference in unit rate). Below that usage the tariff with the lower daily charge wins; above it the lower unit rate does.
Value of a rate difference
Pounds a year = usage in kWh × difference in pence per kWh ÷ 100.
Gas volume to energy
kWh = cubic metres × 1.02264 × calorific value ÷ 3.6, which is the industry conversion your supplier applies.
Benchmarks and how we pick one
A benchmark is the Ofgem capped figure for your region, fuel, payment method and meter type in the period that applies today in Europe/London time. We never mix periods or payment methods in a single comparison. Where a postcode area spans two regions we tell you rather than picking one silently.
VAT and typical usage
Published figures are used exactly as Ofgem states them, including whether VAT is included for that fuel and period. Where you leave usage blank we use Ofgem's typical domestic consumption values, labelled as such — they are a stand-in for your data, not a prediction about your home.
When we hold no figure
If Ofgem has not published a figure for a combination, the site says so. We never interpolate, estimate or carry an old period forward to fill a gap. See the sources and verification dates.