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 electricity 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. Anything else in it is discarded before any calculation runs.
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.
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 over the last 90 days. 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 last three months need not be cheapest over the next three.
A tariff shown without a total is one we do not hold rates for across your whole period. Those are left uncosted rather than costed at zero, because zero-rating the gaps would make the tariff with the least data look like the cheapest — which is the one way a comparison like this could actively push someone into a worse deal.
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.
What the timing figures tell you
The share of your electricity used overnight is what decides whether a time-of-use tariff is worth having. If most of your usage is already in the small hours — a heat pump on a night setting, an electric car charging, storage heaters — a night rate can be transformative. If your usage is concentrated in the evening peak, the same tariff will cost you more than a flat one.
That is the honest way to use this page: not to find the tariff with the lowest advertised rate, but to find out whether your own pattern suits the tariffs that reward shifting. Our reviews of the Agile and Tracker tariffs cover what living with each is like once the arithmetic is settled.