How to Calculate Your Car’s Cost per Kilometre
June 11, 2026 · 6 min read
Cost per kilometre is the single most useful number you can know about your car. It turns every decision — keep the car or sell it, drive or take the train, accept the far-away job or not — into simple arithmetic. And yet most drivers have never calculated it, because the inputs are scattered across fuel receipts, garage invoices, and insurance emails.
The formula
The formula itself is one division:
cost per km = total money spent ÷ total kilometres driven
All the difficulty hides in the two inputs. Get them wrong and the number is meaningless; get them right and you know precisely what a 40 km daily commute actually costs you per month.
What counts as “money spent”
Include everything the car costs you, not just fuel. A useful checklist:
- Fuel — every fill-up, even partial ones.
- Maintenance — oil changes, brakes, tyres, the timing belt you’ll pay for eventually.
- Repairs — the unplanned ones count double, because they’re the ones people conveniently forget.
- Insurance and road tax — annual amounts, spread over the kilometres you drove that year.
- Parking and tolls — if they’re a regular part of using the car.
Depreciation is the controversial one. If you want the true economic cost, include it (purchase price minus expected resale, divided over the kilometres you’ll own the car). If you want the cash cost of driving — “what does one more trip cost me?” — leave it out. Both numbers are useful; just know which one you’re looking at.
A worked example
Say you drove 14,200 km last year in a mid-size petrol hatchback:
| Category | Year total |
|---|---|
| Fuel (≈ 6.8 L/100km) | €1,540 |
| Maintenance & tyres | €620 |
| One unplanned repair | €380 |
| Insurance + road tax | €710 |
| Total | €3,250 |
€3,250 ÷ 14,200 km = €0.23 per km. That 40 km commute? €9.20 a day, roughly €200 a month. Suddenly the monthly transit pass has a price to beat.
Three mistakes that skew the number
- Counting only fuel. For most cars, fuel is 40–55% of running costs. A fuel-only number flatters the car badly.
- Using a short window. One month with no repairs looks cheap; the month the clutch goes looks catastrophic. Use at least six months, ideally a full year.
- Guessing the kilometres. Record the odometer when you start tracking and at every fill-up — don’t reconstruct it from memory later.
Keeping the number current
The calculation is trivial; the discipline of capturing every expense and odometer reading is the real work. A consistent fuel log gets you most of the way. If you’d rather not maintain a spreadsheet, Vroom does this exact arithmetic for you: log each expense with the odometer reading and it keeps your cost per kilometre (or mile) continuously up to date — by week, month, year, or any range you pick.