How we calculate

• Your smart meter records how much electricity you use every half-hour. We use the 12 most recent months of those readings.
• If you have less than a year of readings, we scale what you have up to a full year, following your own pattern of use. The less data, the rougher the estimate, and we tell you when that's the case.
• If some half-hours are missing, we fill each one with your usual usage for that day of the week and time of day.

• Each plan's unit rates are applied to every half-hour of your usage, so a night rate is only charged on what you used at night.
• We add the standing charge (urban or rural, whichever applies to you), the PSO levy, and any extra charge for prepay, then VAT.
• Where a supplier has announced a price change, the new prices are used from the date they start. A fixed-price plan keeps its price for the fixed term.
• If you have solar panels, the payment for the electricity you send back to the grid is taken off, at each supplier's own export rate.
• A welcome bonus or cashback is spread over the length of the contract, so a €100 bonus on a 12-month plan takes €100 off the yearly cost.

Plans are ranked from the lowest yearly cost to the highest. Nothing else goes into the order, and no supplier can pay to move up it.

When you tell us your current plan, we price it on your usage in exactly the same way. The saving shown for any plan is your current plan's yearly cost minus that plan's yearly cost.

Where we show a cost without your own data, such as a supplier's cheapest plan, we use the CRU's typical home of 4,200 kWh a year. That's the same figure suppliers use for the Estimated Annual Bill. Your own usage will almost always give a different answer, which is why we recommend comparing with your smart meter readings.

We check every supplier's published prices regularly and compare them against what we have on file, so changes show up quickly. Electricity only: we don't compare gas. See also ways to pay.