When you register for Cheap Energy Club, we get your annual usage from your supplier via a regulated data energy hub which matches your usage to your address (though you can change these figures if you don't think they're quite right, or if your usage is likely to be different in the coming months).
We then estimate what each tariff in the Club will cost you (per month and annually) based on these usage figures. Though your actual payments may differ.
If you entered what you spend on gas and electricity, we use some assumptions to work out your usage, so the savings you see might not be bang on. Ultimately, the actual difference in what you pay each year will be small, and the cheapest suppliers will likely appear in the correct order.