Cost per kilometre:
adding up fuel, upkeep and the value you lose

The cost that never shows at the petrol pump

Most people estimate the cost of driving by dividing the price of a litre by the kilometres it gives. That figure is real, but it counts only the money that leaves your pocket on the way. The rest of the ownership cost is spread so thinly over each trip that it seems to vanish, yet it is paid in full over the year.

Four groups of costs sit behind the fuel figure. Servicing and repairs are payments for keeping the car running. Insurance and road-tax-type charges are paid whether the car moves or not. Tyres and brake pads are consumed by use. And depreciation is the unseen one: the difference between what you paid and what the car will fetch when you sell it.

Putting them all in one rupee-per-kilometre number lets you compare very different options, such as owning a car, using a cab, or taking a train and an auto for the last mile.

The formula: split each cost over the distance

Fuel and tyres scale directly with distance, so they are per-kilometre costs by nature. Insurance and depreciation do not; they are annual costs that happen to be divided by your kilometres. That difference decides what happens when you drive more or less.

The inputs below are assumptions for one example, not market data. Replace them with your own bills.

A cost per kilometre also differs by car type: diesel and CNG vehicles have lower fuel costs per km but usually higher purchase prices and servicing, and electric cars shift the balance again, with very low energy cost per km and a depreciation figure that is hard to predict. The same formula works for all of them, only the inputs change.

Worked example: a 12,000 km year

Fuel is ₹6.67 of the ₹17.30, about 39%. The cost that most drivers would quote from memory is less than half the true cost per kilometre.

Why driving more makes each kilometre cheaper

Insurance and depreciation do not depend much on how far you drive, so they behave like a fixed monthly bill. In the example they total ₹1,00,000 a year. The variable part, fuel, upkeep and tyres, is ₹8.97 per km. Cost per km is then fixed ÷ distance + variable.

A car driven only on weekends at 6,000 km a year costs nearly twice as much per kilometre as the same car driven daily. That does not mean driving more saves money in total; it means each extra kilometre costs only the variable part, which is useful when you decide between a short drive and a cab.

Checking the figure against a cab fare

Suppose a ride-hailing cab charges ₹14 per km plus waiting and a base fare, and you make 25 km trips. Comparing ₹14 with the full ₹17.30 per km makes the cab look expensive. Comparing it with the variable ₹8.97 per km makes the car look cheap. Neither is the whole truth, and the right comparison depends on whether you would still own the car if you stopped using it.

If you would sell the car, the full cost is the one to compare, and the saving is the whole of the fixed part as well as the variable. If you would keep it for other uses, only the variable cost is saved by taking a cab, and the cab has to beat that. Many urban households find that their car is cheaper than cabs only above a certain number of trips a week, and the cost-per-km table shows the point where that happens.

At 25 km per trip the variable cost of the car is ₹224 and the full cost is ₹432, against about ₹350 for the cab before waiting charges and surge pricing.

Using the figure for real decisions

• Cab versus own car: compare the cab's fare per km with your variable cost for a single trip and with the full cost if the car would otherwise sit idle.
• Car-pooling: dividing the variable cost among riders is fair; dividing the full cost is generous to the passengers.
• Reimbursement: many employers pay a fixed rate per km, and the full cost per km tells you whether it covers the car.
• Replace or keep: a rising servicing bill is easier to judge when you can see it in rupees per km next to a new car's depreciation.

Keep a simple log. Note the odometer and the litres at each fill-up, write down every service and tyre bill, and record the insurance renewal. After a year you have your own cost per kilometre, and it will be more accurate than any estimate from a brochure.

Inputs that move the answer most

Mileage is the input people overstate. The figure printed on the brochure comes from a test cycle, while real city driving with air conditioning often returns 20% to 30% less. Use your own tank-to-tank average for a month.

Depreciation is the other large one and the hardest to know. Check what similar used cars sell for today rather than guessing, and remember that the first couple of years take the biggest fall. Loan interest, if you borrowed to buy, is a further cost that this example leaves out.

Finally, add parking, tolls and fines if they are a regular part of your driving. They are easy to forget and can add more per kilometre than tyres.