Read the tariff before dividing the headline by twelve
The useful starting point is four prices: electricity per kilowatt-hour, electricity per day, gas per kilowatt-hour and gas per day. A standing charge continues on days when consumption is zero. Ofgem’s cap constrains the combination of prices on covered tariffs; it does not give everyone an identical bill. Region, payment method and meter arrangement matter. Fixed tariffs, heating oil and heat-network charges are outside this particular protection. [2]
Dividing £1,723 by twelve produces £143.58. That division is correct, but its meaning is narrow: one twelfth of the published annual benchmark. It does not reconstruct your October charge. The calculation contains no information about your meter readings, whether you cook with gas, how many days the bill covers or the temperature you maintain at home.
A supplier’s proposed monthly payment is another number again. Ofgem explains that a regular Direct Debit can create credit during lower-use months that helps cover higher winter use. [3] To understand a change, put the tariff charge for energy used beside the payment requested and the account balance. Those three figures answer different questions.
A clean comparison holds usage and days still
The examples below are invented teaching tariffs in GBP, with all taxes already included. They are not Ofgem’s October rates, regional quotes or supplier offers. We use them because a transparent comparison is more useful than mixing an average electricity price with an unmatched regional gas price.
The fictional old tariff charges 25p per electricity kWh and 60p per day, plus 6p per gas kWh and 30p per day. The fictional new tariff charges 27p and 55p for electricity, plus 7p and 32p for gas. Every example covers the same 90 days and keeps consumption unchanged between tariffs.
| Household scenario | Electricity / gas kWh | Old charges | New charges | Difference |
|---|---|---|---|---|
| Lower gas use | 450 / 900 | £247.50 | £262.80 | +£15.30 / 6.2% |
| Middle example | 750 / 3,000 | £448.50 | £490.80 | +£42.30 / 9.4% |
| Higher gas use | 1,050 / 6,000 | £703.50 | £781.80 | +£78.30 / 11.1% |
These are three selected usage patterns, not official low, medium and high consumption bands. The same tariff change produces three percentage increases because the households buy different quantities of each fuel. The fixed charge contributes the same cash difference in every row; the usage component does not.
Find the component that moved
For the middle example, electricity usage costs rise from £187.50 to £202.50. Its standing charge falls from £54 to £49.50. The net electricity increase is therefore £10.50. Gas usage costs rise from £180 to £210 and its standing charge rises from £27 to £28.80, adding £31.80. Together, those changes account for the entire £42.30 difference.
The general calculation is simple: multiply each fuel’s kWh by its price in pounds, add the daily standing charge multiplied by bill days, then add the two fuels. Convert pence to pounds before adding. If a published price already includes tax, adding tax again overstates the result.
This breakdown also makes a useful diagnostic. An unexpectedly large total might come from more consumption rather than a larger tariff increase. It might combine both. Rebuilding the invoice component by component gives you a specific discrepancy to discuss with the supplier instead of a disagreement over a headline percentage.
Winter can change the quantity as well as the price
Suppose the middle household instead uses 3,600 gas kWh under the new fictional tariff, with electricity unchanged. Its new total is £532.80. Compared with the original £448.50, the increase is £84.30. Only £42.30 is the same-usage tariff effect; the other £42 is the extra 600 gas kWh priced at 7p.
That is why comparing a summer invoice with a winter invoice cannot isolate a tariff change. The number of days may differ, the heating may run longer and a previous estimate may have been corrected. A useful worksheet first prices one fixed consumption basket twice, then adds a separate scenario for changed use.
For an electricity-only home, omit gas entirely, including its standing charge if there is no gas supply charge on the account. For a multi-rate meter, separate consumption into the relevant bands. A single blended electricity price cannot tell you whether a shift towards expensive hours will outweigh cheaper off-peak use.
What to check on the first bill after a change
- Match the tariff name, payment method and region to the supplier’s notice.
- Check start and end dates, charged days, and whether the readings are actual or estimated.
- Find each unit price and standing charge, including the date on which it changes.
- Use billed gas kWh, rather than treating a gas-meter volume reading as electricity-style kWh.
- Separate energy charges from credits, debt payments and the account balance.
- Keep a copy of the notice alongside the invoice so a disputed line can be identified precisely.
A bill crossing a tariff-change date needs the appropriate allocation between periods. Do not apply the new rate retrospectively to every unit simply because the invoice arrived in October. Ask the supplier to explain the allocation if the bill does not make it clear.
There is also a source limitation worth preserving. At our check, Ofgem’s rates page labels the October period but retains a July–September heading for its standard-credit section, and its electricity VAT wording differs from its general billing explainer. We therefore do not present a regional before-and-after bill as verified. Use the dated, tax-labelled prices in your own supplier notice for that calculation. [1] The three scenarios above remain explicitly fictional; none is a prediction of your next payment.
Read the underlying guidance.
- Energy price cap unit rates and standing chargesOfgem · checked 2026-09-28. October–December 2026 headline; regional/payment variation; period and tax-label limitations.
- Energy price cap and standing charges explainedOfgem · checked 2026-09-28. Cap scope, exclusions and distinction between unit prices and total bill.
- How your electricity or gas bill is calculatedOfgem · checked 2026-09-28. Tariff components and Direct Debit credit; general tax wording not used for the model.
Source and arithmetic checks by the producing AI, followed by a separate AI editorial review. Human English editing and subject-specialist review have not been completed. Human energy-specialist and English-editor review; supplier-specific rates required for a personal estimate.
