Running cost per kilometre: how to work it out properly

Ask a fleet owner what their cost per kilometre is and you will usually get an answer. Ask how it was calculated and the answer is almost always fuel, divided by distance, plus something for maintenance.

That figure is not wrong so much as incomplete — and incomplete in a direction that consistently flatters the fleet. It is why routes that look profitable on paper lose money, and why the loss is hard to locate afterwards.

What actually belongs in the number

Running cost splits into three groups, and most informal calculations only cover the first.

Costs that scale with distance

Fuel is the obvious one. Tyres are the one most often left out, and they matter more than people expect: a tyre has a life measured in kilometres, so every kilometre consumes a calculable fraction of its cost. The same logic applies to engine oil and consumables tied to running.

Tolls also belong here, though they scale with route rather than distance — which is exactly why they need attributing to trips rather than treated as a monthly lump.

Costs that scale with time or usage

Servicing falls due on distance or hours. Repairs are irregular but real. Spare parts and workshop labour belong here, and this is where informal calculations break down most often, because a repair is remembered as an event rather than recorded against the vehicle that needed it.

If your workshop consumes parts without booking them to a specific vehicle, you cannot build a real cost per kilometre. The parts left inventory, but you cannot say which asset consumed them.

Costs that are fixed regardless of movement

Insurance, registration, road tax, permits and fitness. A vehicle that sat idle all month still incurred these. Excluding them makes a lightly used vehicle look cheap to run, when the opposite is usually true — its fixed costs are spread over fewer kilometres.

This is the group people leave out precisely because it feels unrelated to running. It is what makes an idle vehicle look fine until somebody asks why the fleet is not making money.

Depreciation, and being honest about it

Depreciation is not a cash cost, which is why operational calculations usually skip it. For deciding whether to accept a load tomorrow, skipping it is defensible.

For deciding whether to keep the vehicle, it is not. A vehicle wears out over a usable life, and if you are not setting aside for replacement, a profitable-looking fleet is quietly consuming its own capital.

The practical compromise most operators land on is to track two numbers: a cash cost per kilometre for pricing decisions, and a full cost per kilometre including depreciation for fleet decisions. They serve different questions and neither replaces the other.

Why distance is harder to capture than cost

The denominator causes more trouble than the numerator.

Odometer readings taken irregularly, or written down and keyed in later, produce distances that drift. Where a reading is missed for a month, the following month absorbs two months of running and every per-kilometre figure for both months is wrong.

For equipment that does not travel — excavators, generators, plant machinery — distance is the wrong unit entirely. Running hours are the meaningful denominator, and cost per hour is the number that matters. Trying to force these into a per-kilometre figure produces something meaningless.

The practical way to make the number trustworthy

None of this requires sophistication. It requires that costs land against vehicles as they occur, rather than being reconstructed later:

• Fuel entries recorded against the vehicle and the odometer reading at the time of filling
• Odometer or hour readings captured on a routine, not remembered
• Workshop jobs booked to the vehicle, consuming parts from inventory and technician time
• Tolls attributed to trips rather than pooled monthly
• Insurance, tax, permit and fitness costs held against the vehicle they belong to
• Tyres tracked as items with a life, so their cost spreads across the kilometres they actually serve

Once those six things are true, cost per kilometre stops being an estimate and becomes a report. The arithmetic was never the difficulty; the record-keeping was.

What the number is actually for

A trustworthy cost per kilometre changes three decisions:

1. Pricing. You can tell whether a rate covers its costs before accepting it, rather than discovering it at year end.
2. Replacement. Rising cost per kilometre on an ageing vehicle is the clearest signal you will get that it is due for replacement — but only if maintenance is genuinely captured.
3. Comparison. Two similar vehicles on similar work should produce similar figures. When they do not, the difference is worth investigating — driving style, a developing mechanical fault, or a recording gap.

That third one is the most useful and the most commonly missed. The value is not the absolute figure; it is the variance between vehicles that should match.

If you want to see how this is captured against real vehicles, see how our fleet and workshop system tracks it, or book a demo with your own cost heads.