All gas and electricity tariffs shown in the results tables are currently available energy tariffs. We assume that you are on a current tariff and not a historical tariff no longer available from the supplier. Please bear in mind that this may impact upon the calculations given. In order to compare prices, it is best to enter the number of kilowatt hours that you use as opposed to the amount of money you spend. If you do not have the kWhs, then you can enter the amounts you pay monthly, quarterly or annually. When you do this, the calculator works out how many kWh's you use, but it uses the latest available tariffs to do this and does not take into account any changes to the rates for that tariff. It will then use the calculated number of kWh's to work out what each supplier will charge for the next 12 months based on existing tariffs. The results page shows how the suppliers compare to each other for the same amount of energy used.