Working out your car’s real cost per kilometre
One number that tells you what driving actually costs you: how to work it out from your receipts, what to count, and the one fill-up to leave out.
Ask most drivers what their car costs and they'll name the monthly fuel bill. Fuel is the part you notice, but services, repairs, tyres, parking and car washes all add up. Cost per kilometre puts all of it into one number you can compare month to month, or car to car.
The arithmetic
Cost per kilometre is everything you spent on the car over a period, divided by the distance you drove in that same period.
Cost per km = money spent ÷ kilometres driven
For the distance, use your odometer: the reading at the end of the period minus the reading at the start.
A worked example
Say that over the last 90 days you spent:
| What | Amount |
|---|---|
| Fuel | $540 |
| A service | $135 |
| Parking and a car wash | $45 |
| Total | $720 |
At the start of the period the odometer read 80,000 km, and at the end 86,000 km: 6,000 km driven.
$720 ÷ 6,000 km = $0.12 per km
The fill-up to leave out
There's one trap. The fuel from your first fill-up in the period was mostly burned before the period started: it's what got you to the pump. Count it, and the figure comes out too high. Leave out the fuel of the first fill-up, and count every one after it.
What to count
- Fuel, from every fill-up but the first.
- Servicing and repairs: oil changes, parts, labour, tyres.
- Other running costs: parking, tolls, car washes, and renewals such as insurance and registration if you want the full picture.
A big repair can make one month look expensive. That's why a longer window, such as 90 days, gives a steadier figure than a single month.
What it tells you
Watch the number over time. If it creeps up while you drive the same way, something has changed: fuel prices, a dragging brake, under-inflated tyres, or a car that's starting to need more repairs. It's also a fair way to compare two cars, or to see what a long commute really costs.