Selecting your vehicle
On the first screen you need to select your vehicles for comparison. Firstly choose a pure electric vehicle or plug-in vehicle; the default shows you new cars that are available to buy now, but you can also select the Used button to find any plug-in car that has been on sale in the UK. Next select your comparison vehicle, this can be another plug-in vehicle or a petrol / diesel / hybrid car.
Adding your journey details
On the input screen you are asked to provide details about your journey distance – you can either enter a mileage value or, using the Plan a route option, enter the start and destination of a typical journey and the tool will calculate the distance. The default journey frequency is daily, but you can change to monthly or annually as desired.
The home electricity cost, which will be used to calculate your electricity costs, defaults to the UK average. Source: UK Government – updated annually. You can edit and change to your own tariff if you wish.
If you have chosen a petrol, diesel, hybrid, or plug-in hybrid you will also be able to change the default cost per litre. The default shows the UK average from Petrol Prices and is updated monthly.
Your journey cost results
Your journey costs using the two vehicles selected are calculated using the vehicle, distance, and fuel price data selected or entered via the mapping tool. The results are displayed in three ways together with a cost comparison over a year:
1. Journey fuel costs = fuel economy x miles x fuel price. Results are rounded to the nearest whole £pound.
2. Cost per mile = fuel economy x fuel price. Results expressed in pence per mile.
3. Total annual fuel costs = fuel economy x miles x fuel price x journeys per year.
Results are rounded to the nearest whole £pound.
Note that, for all new cars, official CO2 and MPG emissions are generated using the Worldwide Harmonised Light Vehicle Test Procedure (WLTP), which replaces the New European Drive Cycle (NEDC) as the mandatory test protocol. Unlike NEDC test data, different model trim options (such as a performance pack, wheel size or body upgrades) may result in changes to the official CO2 and MPG figures. In these cases, the range of possible WLTP CO2 emissions is shown, together with the range of tax rates payable (where these are emissions-dependent). In all cases, an estimate of real-world MPG (based on WLTP MPG) is used to calculate journey costs.
More details on fuel economy calculations by vehicle type
A vehicle’s fuel cost is calculated by multiplying its fuel economy (using units of litres or kWh per 100 km) by fuel price (in pence per litre or kWh) and the distance driven (in kilometres). Inputs and results are shown in imperial units (miles per gallon, pence per mile, and miles) using appropriate conversion factors.
Electric vehicles
For vehicles powered solely by electricity, fuel cost is calculated by multiplying the fuel economy (in kWh per 100 km) by fuel price (in pence per kWh) and the distance driven (in kilometres or miles). The real-world electric cost is calculated using real-world driving tests, or where not available, estimated from official test figures for fuel economy.
Plug-in hybrid vehicles
For plug-in hybrid vehicles powered by electricity and petrol or diesel, fuel cost for both fuels is calculated multiplying the fuel economy (in litres and kWh per 100 km) by fuel price (in pence per litre and kWh) and the distance driven (in kilometres or miles). The fuel cost is estimated using the assumption that the vehicle is driven for half the distance in electric-only mode and half using a conventional fuel (‘Condition B’); real-world figures are used for both figures.
Petrol, Diesel, and hybrid vehicles
For vehicles solely powered by petrol or diesel, fuel cost is calculated by multiplying the fuel economy (in litres per 100 km) by fuel price (in pence per litre) and the distance driven (in kilometres or miles). The real-world fuel cost is from real-world driving tests or where not available estimated from test-derived figures (‘official combined’) for fuel economy.
Worked examples
Electric: Nissan LEAF Acenta 40 kWh
| Description | Metric | Imperial |
| Official energy use | 14.6 kWh/100km | |
| Real-world energy use | 16.1 kWh/100km | |
| Electricity price (typical UK average) | 16.5 p/kWh | |
| Distance travelled (1 mile = 1.61 km) | 161 km | 100 miles |
| Real-world journey cost = (16.1 x 1.61 x 16.5 / 100) = £4.28 |
Plug-in Hybrid: VW Passat TSI PHEV 218PS DSG
| Description | Metric | Imperial |
| Real-world Fuel Only fuel economy | 9.4 litres/100km | 30.1 MPG |
| Real-world energy use | 15.6 kWh/100km | |
| Petrol price (typical UK average) | 120.4 p/litre | |
| Distance travelled (1 mile = 1.61 km) | 161 km | 100 miles |
| Real-world journey cost = 0.5 x (15.6 x 1.61 x 16.5 / 100) + 0.5 x (9.4 x 1.61 x 120.4 x 100) / (100 x 100) = £11.18 |
Diesel: BMW 3 Series 318d SE – Diesel, 1995cc
| Description | Metric | Imperial |
| Official combined fuel economy | 4.3 litres/100km | 66.0 MPG |
| Real-world combined fuel economy | 6.1 litres/100km | 46.5 MPG/100km |
| Diesel price (typical UK average) | 120.8 p/litre | |
| Distance travelled (1 mile = 1.61 km) | 161 km | 100 miles |
| Real-world journey cost = (6.1 x 1.61 x 120.8 / 100) = £11.86 |
Notes
All results are based upon the theoretical optimum operating efficiency of the vehicle as quoted by the manufacturer. Please bear in mind that you may achieve very different results in real life. These tools should be used for comparative purposes only.
You can change the fuel cost figure to more closely reflect your experience. The real-world fuel economy figures are based on real-world driving tests or where this data is not available, estimated from official NEDC or WLTP figures (depending on model), which are obtained from the official EU test data. These figures are intended for comparisons between vehicles and may not reflect real driving results.
