How our gas and electricity calculator works

The energy calculator calculates the running cost of each tariff, using information provided by the user when they answer questions such as "Current Supplier" and "Consumption details" and employing some basic assumptions. The calculator then checks through all the tariffs available and calculates the money that can be saved by switching to each one from the current supplier.

In order to build a calculator that applies to everyone and to ensure we do not require users to answer pages and pages of questions, we have to make certain assumptions which are outlined below. Please note the assumptions are applied across all suppliers and tariffs.

Using consumption details

For customers that choose to enter their "consumption details" from their last quarterly bill, our method of annualising this consumption takes into account the time of the year in which the bill was received. This is because quarterly bills will vary depending on which time of the year the bill is produced. So for example a summer bill will generally be cheaper than a winter bill mainly because less energy is needed to heat the home during this time of the year. All of this is taken into consideration when calculating a customer's annual spend.

Creating an estimate based on property type

For customers that have no "consumption details" to hand, we ask a series of questions regarding their household such as the type of property, the number of bedrooms, the quality of insulation etc. The customer's responses for each of these questions provide uSwitch with a profile that enables us to estimate their annual consumption.

The calculator looks at several variables when calculating the bill sizes for each tariff on the results table. It then works out how much the customer could save by switching from their current supplier to each tariff (assuming they use the same amount of gas and electricity).

• Standing Charge (some suppliers charge a fixed daily charge, regardless of how much you use)

• Unit Rates (these are the costs of using one unit or kilowatt-hour of gas or electricity)

• Consumption thresholds (some suppliers charge a different, often lower, unit rate once a customer's gas or electricity consumption has passed a certain threshold)

We only include discounts that are received year on year in our calculations. Introductory or one off discounts are not included, nor are charges that may be received if a plan is cancelled or altered. Contributions made to charity are also not included in the calculated annual bill.

Discounts we include:

• Dual fuel discounts

• Direct Debit discounts

• Paperless billing discount

• Online discount - offered to customers who either sign online or manage their account online

Users can opt to filter out or include tariffs based on the features and preferences they require. If a user for example opts to see only tariffs with no standing charge we will filter out all tariffs that do not offer this facility.

uSwitch.com includes plans that a customer may currently be signed up to in our database of suppliers and tariffs. These include fixed price or capped plans that a supplier previously offered, but has now withdrawn from the market.

Any plans that have been withdrawn are included so the customer can make the most accurate comparison with energy plans available. As they are not available to new customers, they will not be included in our results.