An electric vehicle is the biggest new electrical load most homes will ever add, bigger than the hot water system, and unlike hot water it arrives with a choice: when it charges and what rate it charges at are both up to you. Get those right and running costs embarrass petrol; leave them at defaults and you can pay double what you needed to. The maths is short, so let us do it properly.
The basic numbers
EV consumption is usually quoted in kWh per 100 km, and most passenger EVs land roughly in the 14 to 20 kWh per 100 km range depending on the car, speed and weather. From there it is the same formula as any appliance:
kWh per 100 km × your rate per kWh = cost per 100 km.
Worked examples for a car using 16 kWh/100 km:
- At a 32 c/kWh anytime rate: about $5.12 per 100 km.
- At a 22 c/kWh off-peak rate: about $3.52 per 100 km.
- At an 8 c/kWh EV-plan overnight window: about $1.28 per 100 km.
Same car, same driving, and the yearly gap between the first and last row on 15,000 km is roughly $576. The charger did not change; the tariff did. That is the entire lesson of home EV charging: the rate you charge at matters more than the hardware you charge with.
For scale, a 60 kWh battery charged from near empty is about 60 kWh plus a little for charging losses, and home charging (a standard socket or a wallbox) simply spreads that over hours, which suits overnight windows perfectly.
Matching the car to a tariff
Three realistic setups, in rising order of involvement:
- Single rate. Simple and predictable, and our supply charge maths still applies, since an EV's extra kWh pushes you toward plans with cheaper usage rates even if the daily charge is higher. If you charge whenever and cannot schedule, a sharp single rate is a fine start.
- Time-of-use. An EV is the most schedulable load a home can own: set the car or charger to start in the off-peak window and the whole battery fills at the cheap rate. This is the case where TOU most clearly wins; our time-of-use guide covers the trade-offs, and the one rule that matters is never charging through the evening peak by accident.
- Dedicated EV plans. Some retailers offer plans with very cheap fixed overnight windows or EV-specific rates, sometimes requiring a compatible charger or app. They can be excellent for the car and mediocre for the house: check whether the plan's other rates are competitive, because the household kWh still dwarf many people's driving kWh.
Two cautions. On a demand tariff, a fast home charger drawing hard in the wrong window can set a painful monthly peak; our demand tariff guide explains why one bad half hour lingers. And if you have solar, midday charging from your own panels beats any grid rate; our solar guide covers why self-consumption is worth several times the feed-in credit.
How to compare plans once an EV is involved
Your historical bills understate your future usage, so compare on projected numbers: take your current daily kWh and add the car (annual km ÷ 100 × the car's kWh/100 km ÷ 365; a 15,000 km year at 16 kWh/100 km adds about 6.6 kWh a day). Put that projected daily usage into our free calculator to rank plans on whole-bill cost; pick your State and, in the six eastern States and Territories, import real plans for your postcode. Then, if you can schedule charging, sanity-check the shortlist's off-peak or EV windows against the per-100 km maths above.
An EV raises your usage and lowers your per-kilometre cost at the same time; which effect dominates your budget is decided the day you pick the tariff. Pick it on purpose.