This calculator compares what it costs to run a petrol car against an electric vehicle over a year, including the road user charges that now apply to EVs in New Zealand, so you can see the real saving. Electric vehicles are far cheaper to fuel than petrol cars, because electricity per kilometre costs much less than petrol, but the picture is not as simple as the showroom suggests. Since April 2024, light electric vehicles pay road user charges, currently $76 per 1,000 kilometres, the same as diesel vehicles, which closes part of the gap that EVs once enjoyed. To compare fairly you need to weigh petrol cost against electricity cost plus those charges. This tool does it. You enter your annual distance, your petrol car's fuel economy in litres per 100 kilometres and the petrol price, then the EV's energy use in kilowatt hours per 100 kilometres, your electricity price, and the road user charge rate. The calculator returns your annual saving by going electric, along with the yearly petrol cost, the EV's total yearly cost including charges, and the five-year saving. The results update as you type, so you can test different driving distances, fuel prices and home charging rates. Use it to decide whether an EV stacks up for your driving, to estimate the payback on the higher purchase price, or simply to understand your fuel spending. Charging at home off-peak gives EVs their biggest advantage, while heavy highway driving at public fast chargers narrows it.
Petrol = km/100 x L/100km x price. EV = km/100 x kWh/100km x power price + road user charges. Home off-peak charging gives the biggest saving.
The petrol cost is your distance divided by 100, times litres per 100 kilometres, times the petrol price. The EV energy cost uses the same distance with kilowatt hours per 100 kilometres and the power price, then adds road user charges at the set rate per 1,000 kilometres. The annual saving is the petrol cost minus the EV total.
Driving 12,000 km a year, a petrol car using 8 L/100km at $2.80 costs $2,688. An EV using 18 kWh/100km at $0.28 costs $604.80 in power, plus $912 of road user charges, totalling $1,516.80. The EV saves about $1,171 a year, or roughly $5,856 over five years.
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