Tariff checker: methodology
What it compares
The quotes you bring. There is no list of tariffs here to go out of date and no supplier pays to appear: you copy the rates from each quote’s tariff details, and the checker works out what each would cost your household over the next twelve months.
Your usage, and time bands
With a smart meter file, the checker measures the share of your electricity in each half-hour of the day, from complete days only, and the yearly total as the smart meter data analyser does. Each band of a time-of-use quote is priced on the share of your use that falls in it. Without a file, it uses the typical-home pattern from the Faraday data. Octopus exports also carry what you paid, which the checker reads to offer your current tariff as an option. If the file comes from an earlier price cap period, a variable tariff has moved with the cap since, so the checker scales what you paid by the change in the cap’s electricity rates, which already include any change in VAT.
Price cap scenarios
Nobody knows the next cap until Ofgem announces it (by 25 November 2026 for January). So every quote is priced under three futures:
- No change. The cap stays where it is for the whole year.
- Lower forecast. Up 16% in January, Cornwall Insight’s forecast of 30 September, the lowest published; then down 0.5% in April and 7.8% in July. Source: Cornwall Insight, 30 September 2026.
- Supplier forecasts. Up 26% in January, the average of British Gas, EDF and E.ON Next forecasts on 21 October; then down 0.5% in April and 7.8% in July. Source: Uswitch, supplier average as of 21 October 2026.
A quote marked “follows the price cap” moves by the same percentage as the cap in each scenario; a fixed quote stays put. Discounted trackers keep their discount, which is what their terms usually say.
VAT
Domestic electricity in Great Britain is zero-rated for VAT until 31 March 2027. Quotes made now show those zero-rated prices, so electricity costs are increased by 5% from April onwards, for fixed and variable tariffs alike. Gas VAT doesn’t change.
Across the year
A cap change only touches the months after it, so the checker spreads your use across the year. Electricity follows the Faraday monthly pattern. Gas follows our approximation of a gas-heated home, which is not a published series; it only decides how much of the year falls either side of a price change. As a check, distribution-network gas demand (homes and small businesses together) swings about four to one between January and August (Oxford Institute for Energy Studies), and homes alone swing harder.
| Month | Share of a year’s gas |
|---|---|
| January | 16.2% |
| February | 14.1% |
| March | 12.1% |
| April | 8.1% |
| May | 5.1% |
| June | 3.0% |
| July | 2.5% |
| August | 2.5% |
| September | 3.5% |
| October | 7.1% |
| November | 11.1% |
| December | 14.6% |
The cost of leaving a fix early
A fix with no exit fee is insurance: if prices rise you are protected, and if they don’t you can leave once the cap is announced. For each fixed quote the checker works out what that would cost if prices held: the extra paid until the next cap starts, against the cheapest cap-following quote in your comparison, plus exit fees for each fuel.
What it leaves out
- Regional prices for the price cap option, which uses national averages. Your own quotes are better.
- Dynamic tariffs whose prices change every half-hour, like Agile. They can’t be described as fixed bands.
- Shifting your use. It prices how you use energy now.