A bill can fall while nothing about the household changes. Hold electricity use at 300 kWh over 30 days and move only from Great Britain's price cap for 1 July to 30 September 2026 to the cap for 1 October to 31 December 2026, and the total falls from £95.49 to £95.41 — because the average unit rate rose from 26.11p to 26.32p per kWh while the average daily standing charge fell from 57.19p to 54.83p (Ofgem's price cap unit rates and standing charges). The condition that changes the sum is tax: Ofgem states there is no VAT on electricity from 1 October 2026 to 31 March 2027 and warns that costs cannot be compared directly with previous periods because of it.
Two cap periods and the same 300 kWh
Every figure below uses the Great Britain averages for Direct Debit customers, 30 days, and no other charges.
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| Scenario | Electricity used | Unit rate | Standing charge | Total |
|---|---|---|---|---|
| 1 July to 30 September 2026 cap | 300 kWh | 26.11p per kWh | 30 × 57.19p = £17.16 | £95.49 |
| 1 October to 31 December 2026 cap | 300 kWh | 26.32p per kWh | 30 × 54.83p = £16.45 | £95.41 |
| Same cap, 5% less used | 285 kWh | 26.32p per kWh | 30 × 54.83p = £16.45 | £91.46 |
The arithmetic, line by line: 300 × 26.11p = 7,833p, plus £17.16, is £95.49. Then 300 × 26.32p = 7,896p, plus £16.45, is £95.41. Then 285 × 26.32p = 7,501.2p, plus £16.45, is £91.46.
Row two is 8 pence cheaper than row one on identical consumption. Row three is £3.95 cheaper than row two, and that £3.95 is the only saving in the table that any change of behaviour produced.
Where the money actually moved
Four things can move a total, and only one of them is energy: the quantity of units, the price per unit, the number of days charged, and any adjustment, credit or tax change applied to the account. The first two pull against each other in the table above. The third is the quiet one — a 28-day period and a 31-day period differ by three standing charges before a single unit is counted, which at 54.83p is £1.64.
Tax is the fourth, and it is not small. Eurostat puts taxes and levies at 28.9% of the EU average household electricity price in the second half of 2025, with VAT alone at 15.2%, against an EU average price of €0.2896 per kWh (Eurostat's electricity price statistics). The share ranged from 49.1% of the total price in Denmark down to negative values in Luxembourg and the Netherlands, where allowances outweighed the taxes. A change of that size can swamp a real reduction in use, in either direction.
Ofgem's own explanation of a bill separates the unit rate from the standing charge, and lists wholesale, network, policy and operating costs, the supplier's earnings before interest and tax, and VAT as the components behind them (how your electricity or gas bill is calculated). None of those lines is a measure of how much energy a home used.
Read the bill in the order that answers the question
Work through it together with one person on the quantity column and the other on the money column, and do not let either speak for the other.
First, find the date range and the energy quantity with its unit, and note whether the reading is actual or estimated. Second, divide by the number of days to get a daily average, so two periods of different length can be compared at all: 300 kWh over 30 days is 10 kWh a day, and 285 kWh over 30 days is 9.5 kWh a day. Third, and only third, separate the consumption charge from the standing charge, taxes and any adjustment. Fourth, check whether the payment you are looking at settles that period or is a fixed monthly instalment against an account, because a lower Direct Debit is not evidence of anything.
Then write the sentence out in full. Not "we saved", but something closer to: "we used 5% fewer units in the same 30 days under the same cap, and the total fell by £3.95." It is longer, and it is the only version either of you can defend. If the units themselves are still slippery, settle them first at the kitchen table; if you have not yet copied the record cleanly, start with a home energy observation; and when an appliance is the suspect, the declared figure is on its label, which is worth reading together.
Sources
- Energy price cap unit rates and standing chargesAccessed September 17, 2026
- How your electricity or gas bill is calculatedAccessed September 17, 2026
- Electricity price statisticsAccessed September 17, 2026