How to Calculate EV Charging Costs in NZ

Charging at home is far cheaper than public fast charging, but the actual dollar figure depends on your power plan and your car. Here's how to work it out.

Start with your electricity rate

Your home charging cost begins with your power plan's per-kWh rate. Standard NZ residential rates typically sit around 28-35 cents per kWh, though this varies by region and retailer. If your plan includes an EV-specific off-peak rate — several NZ retailers now offer these — overnight charging can drop to around 12-20 cents per kWh, which is worth checking for and switching to if you charge at home regularly.

Know your car's battery size and efficiency

Every EV lists a usable battery capacity in kWh — for example, a popular small EV might have a 50-60kWh battery, while a larger SUV could be 75-100kWh. Efficiency is usually quoted in kWh per 100km, commonly somewhere between 15-20kWh/100km for most passenger EVs, though this varies with driving style, terrain, and weather.

Run the basic formula

The core calculation is: battery size (kWh) × your electricity rate ($/kWh) = cost of a full charge. For example, a 60kWh battery charged fully on a standard 30 cent/kWh rate costs around $18 for a full charge. On an EV-specific off-peak rate of 15 cents/kWh, that same charge drops to around $9.

Convert that into cost per kilometre

To compare against petrol costs meaningfully, divide the full charge cost by your car's real-world range. If that $18 charge gives roughly 350km of range, that works out to about 5 cents per kilometre — considerably cheaper than the equivalent petrol cost per kilometre for most vehicles at current fuel prices.

Account for charger efficiency losses

Home chargers aren't perfectly efficient — some energy is lost as heat during charging, typically around 10-15% depending on the charger and cable. This means the actual electricity drawn from the wall is somewhat higher than the battery capacity alone suggests, so real bills run a little higher than the simplest version of the calculation implies.

Factor in your charger type

A basic granny charger plugged into a standard household socket charges slowly but uses the same power overall as a dedicated home wallbox — the difference is speed, not cost per kWh. Dedicated home EV chargers, sold by retailers and installers around NZ from roughly $800-$1,800 installed, charge faster but don't inherently change your per-kWh electricity cost.

Worked example

Say you drive 1,000km a month in an EV using 18kWh/100km. That's 180kWh of charging a month. At a standard rate of 30 cents/kWh, that's $54 a month. On an EV off-peak plan at 15 cents/kWh, the same driving costs around $27 a month — a saving worth chasing if you can shift most charging to overnight.

Compare against your current petrol spend

To make the comparison real, work out what the same monthly driving currently costs in petrol and put the two numbers side by side. Most EV owners in NZ find home charging costs a fraction of equivalent petrol spend, particularly when paired with an off-peak electricity plan.