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    How We Calculate Energy Costs and Predictions

    Plain-English explanation of where our numbers come from, the assumptions we use, and how we produce 6-month forecasts. Reviewed by the Power Guardian Energy Analyst Team and updated whenever Ofgem or wholesale markets move materially.

    Based on UK household data

    Ofgem TDCV usage assumptions

    Updated daily

    Wholesale & tariff data refreshed every weekday

    Independent

    No commissions from suppliers

    Estimates are indicative

    For guidance — not financial advice

    How we calculate annual bills

    For every tariff we list, the annual cost is calculated as:

    annual cost = (electricity unit rate × elec kWh)
            + (electricity standing charge × 365)
            + (gas unit rate × gas kWh)
            + (gas standing charge × 365)

    Unit rates and standing charges come directly from each supplier's published rate cards, cross-checked against the latest Ofgem default tariff cap before publication.

    Household assumptions we use

    Unless you give us your own usage, we use Ofgem's Typical Domestic Consumption Values (TDCV) for a medium dual-fuel household:

    • Electricity: 2,700 kWh per year
    • Gas: 11,500 kWh per year
    • Payment method: Direct debit (most common in the UK)
    • Region: National average — regional variations shown separately on the regional pricing pages

    Smaller households (1–2 people) typically use ~1,800 kWh elec / 8,000 kWh gas; larger households (4+) typically use ~4,100 kWh elec / 17,000 kWh gas. Use our postcode estimator to refine for your home.

    Where the data comes from

    • Tariff data: direct from each supplier's published rate cards (refreshed within 48 hours of any change).
    • Price cap: Ofgem's quarterly default tariff cap announcements.
    • Wholesale prices: ICE Futures Europe and NBP (gas) end-of-day settlements.
    • Storage levels: Gas Infrastructure Europe (GIE) AGSI feed.
    • Demand & grid mix: National Grid ESO data portal.
    • Policy & statistics: Department for Energy Security & Net Zero (DESNZ).

    How we produce forecasts

    Our 6-month outlook combines four inputs into a single estimate per quarter:

    1. Wholesale curve: ICE / NBP forward gas & power prices for the relevant quarter.
    2. Cap mechanics: Ofgem's published methodology for translating wholesale costs into the cap.
    3. Storage & supply risk: GIE storage levels and announced LNG flows.
    4. Policy levers: Known DESNZ / Ofgem changes to network costs, levies and standing charges.

    We publish a single central estimate, a confidence label (high / medium / low), and the main drivers behind the number. Forecasts are revised whenever the wholesale curve moves more than ±5% or Ofgem confirms a methodology change.

    Limitations & what we don't claim

    • Estimates are indicative. Your actual bill depends on your meter type, usage pattern and region.
    • Forecasts are not guarantees — geopolitical events can move the cap quickly.
    • We do not include exit fees, late-payment fees or admin fees in the headline annual cost (these are shown separately).
    • We do not receive commission from suppliers for tariffs we list.
    • We are not regulated to give financial advice. Always confirm pricing with your supplier before switching.

    Primary data sources

    Figures are checked against primary sources before publication. See our methodology for details.

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