Is it worth switching energy offer?
Put the contract you have and the offer you were given side by side on the items that really change, the unit rate and the standing charges, and see the gap over a year.
The numbers you type stay in your browser, nothing is sent anywhere.
What gets compared, and why it works
The tool compares only the items the two offers actually quote, that is the commodity (electricity or gas) and the commercial standing charges. Everything else on the bill, network use, meter management, system charges and excise duty, is regulated: with the same meter and the same consumption you pay it identically whoever supplies you, so it disappears when you take the difference between two offers. That is why there is no tariff hidden in the code here and no number that goes stale.
The calculation we do NOT do
We never divide the bill total by the kWh and call it the real price per kWh. That figure mixes commodity, network, system charges, excise and VAT, while offers quote the commodity alone: comparing the two makes any offer look like a bargain. What you read at the bottom is the difference between two contracts, not a bill.
Where to find the numbers
Yearly use is in the consumption summary of your bill, in kWh for power and in standard cubic metres for gas. The kWh in each time band are in the same box, and the real ones matter: two banded offers swap places depending on how much you use in the evening and at the weekend. Rate, spread and standing charge are in the terms and conditions of the proposal. Watch the unit, because a rate written in cents or in €/MWh is a hundred or a thousand times the one in euro per kWh, and that is the most common mistake.
Fixed or indexed, and the break even index
An indexed offer follows a wholesale index (PUN for power, PSV or TTF for gas) and adds the supplier spread, so it moves every month. Comparing it with a fixed rate only makes sense if you state the assumption, and the assumption here is that the index stays at the value you typed. That is why the tool also works out the break even index, the average level at which the two offers cost the same. Above it the fixed rate wins, below it the indexed one does.
Standing charges and the break even consumption
When one offer has the lower unit rate but the higher standing charge, there is an exact consumption where the two meet: the difference between the standing charges divided by the difference between the unit rates. Below it the low standing charge wins, above it the low rate wins. This is why the same offer can be excellent for a family of four and terrible for a holiday home.
Declared limits
The result is an estimate at constant consumption and ignores deposits, exit fees, back billing, social discounts, rebates tied to direct debit or paperless billing, and the length of the fixed period, which is often twelve or twenty four months and deserves a look before you sign. Compulsory add on services such as insurance or boiler maintenance have to be added by hand to the standing charge. For gas the conversion between €/MWh and €/m³ uses the conventional value of 10.69 kWh per standard cubic metre (gross calorific value 38.52 MJ/m³): if the offer already quotes in €/m³, use that. This is not advice and does not replace reading the contract.