What would each tariff have cost you?
Every tariff comparison you have ever seen is built on an assumed household. This one is not. Give it your own half-hourly readings and it works out what each tariff would actually have charged you for the energy you actually used.
Where to get your data
Any supplier with a smart meter can give you your half-hourly consumption, usually as a CSV download from your online account. Look for “usage”, “consumption data” or “download my data”. You are entitled to it — it is your data, and a supplier has to provide it on request.
The file needs a date-and-time column and a consumption column in kWh. If it also carries what each half hour cost — Octopus’s export labels that field as an estimate — the page can compare that complete energy-cost column with what each tariff would have cost. It does not turn an incomplete column into a bill total. Anything else in the file is discarded before any calculation runs.
Ask for as long a history as your supplier will give you. A full twelve months covers a winter as well as a summer, which is the difference between knowing a tariff suits you and knowing it suited you in July.
Your data stays on your device
This matters more than it might sound. Half-hourly consumption is one of the most revealing files a household owns: it shows when you are in, when you sleep, when the house is empty and for how long. Supplier exports also often carry your MPAN, meter serial and account number.
So the file is read and costed entirely in your browser. It is never uploaded, never stored and never logged, and no request made by this page depends on anything in it — the rates below were fetched before you chose a file. The identifying columns are stripped before any arithmetic, and the tool shows you which ones it dropped.
Replay your own smart-meter data
Download your half-hourly consumption from your supplier and drop the file in below. It is read in your browser and costed against each tariff here. The file is never uploaded — it does not leave this device.
Choose gas or electricity above first. A gas export and an electricity export look identical — same columns, same headings — so the only way this tool knows which it is costing is that you tell it.
Your file is read in this browser tab and discarded when you leave the page. Nothing is uploaded, stored or logged, and the identifying columns are removed before any calculation. Costs are worked out from published rates including VAT and are an illustration, not a quote.
How to read the result
The total is what your actual usage would have cost on past published rates from the rate window stated by the tool above. It is not a prediction of a future bill, and it is not a quote. Rates change, and a tariff that was cheapest over the held window need not be cheapest over the next few months.
Every tariff in the table is costed over the same stretch of your readings, and the page says which stretch that is. That matters more than it sounds: some tariffs have only been publishing prices for a few weeks, so costing one over a year and another over a fortnight would rank whichever had the least history against the fewest days of your usage. Tariffs that cannot cover the period are listed underneath with the date their prices start, rather than shown as a blank row — and you can pick a shorter period to bring them in.
Standing charges are shown separately from energy costs on purpose. A low unit rate with a high standing charge is the classic trap in tariff comparison, and it bites hardest on households that use very little. Our standing charge guide goes through when that trade-off is worth taking.