Calculating the fuel cost of a trip in 2026: method, mileage scale and tools

How to calculate the fuel cost of a trip and optimize your fleet management

The fuel cost of a trip is calculated as follows: (distance in km / 100) × the vehicle's average consumption (L/100 km) × the price per liter, to which tolls and parking are added. For a journey reimbursed through mileage allowances, the official 2026 scale offers a flat-rate alternative, from €0.370 to €0.697 per km depending on the vehicle's fiscal horsepower.

Why calculate the fuel cost of a trip precisely?

Fuel remains, along with maintenance, one of the two largest cost items for a business vehicle — and the most volatile from one year to the next. Working at the level of the individual trip serves five purposes: budgeting, route optimization, detecting abnormal over-consumption, billing accurately, and steering the fleet's carbon footprint.

A company that only tracks this item globally, through fuel card invoices, loses the ability to identify which vehicle, which driver or which type of journey weighs most. That is the difference between a cost endured and a lever managed.

What affects a trip's fuel consumption?

• Vehicle and powertrain type: city car, van or heavy goods vehicle, petrol, diesel, hybrid or electric — each has its own consumption.

• Distance and terrain: a hilly route consumes more than flat ground over the same distance.

• Driving conditions: high speed, sharp acceleration and braking, frequent stops in dense traffic.

• Load and weather: a loaded vehicle, headwind, air conditioning.

• Vehicle condition: tire pressure, clogged air filter, engine maintenance.

Calculating a trip's fuel cost, step by step

1. Establish the vehicle's average consumption

Fill the tank, note the mileage, drive normally until the tank is nearly empty, then refill, noting the liters added and the kilometers covered. The calculation: (liters consumed / kilometers covered) × 100. The manufacturer's figure is a reference point, but real consumption often departs from it.

Example: 45 liters for 600 km → (45 / 600) × 100 = 7.5 L/100 km.

2. Determine the distance

A mapping tool gives the distance between departure and arrival. Remember to include planned detours and stops, which add up quickly on a round.

3. Obtain the fuel price

Prices recorded at every French filling station are published in real time on prix-carburants.gouv.fr. For a company budget estimate, an average price over the period, or the price negotiated with the fuel card provider, is more useful than an instantaneous reading that moves every week.

4. Include the additional costs

Tolls, parking and, indirectly, the wear linked to kilometers covered complete the real cost of a business journey.

5. The full formula

Fuel cost = (distance in km / 100) × average consumption (L/100 km) × price per liter (€/L)

Total trip cost = fuel cost + tolls + parking

Example: a 350 km trip with €20 of tolls, a vehicle at 7.5 L/100 km, fuel at €1.80/L → fuel cost = 3.5 × 7.5 × 1.80 = €47.25; total cost = €67.25.

The 2026 mileage scale: the flat-rate alternative

For journeys reimbursed through mileage allowances, or for the actual-expenses option on income tax, the French tax administration publishes a flat-rate scale by fiscal horsepower. The 2026 scale, applicable to 2025 income, is as follows:

Fiscal horsepower	Up to 5,000 km	From 5,001 to 20,000 km	Above 20,000 km
3 CV and below	d × 0.529	(d × 0.316) + 1,065	d × 0.370
4 CV	d × 0.606	(d × 0.340) + 1,330	d × 0.407
5 CV	d × 0.636	(d × 0.357) + 1,395	d × 0.427
6 CV	d × 0.665	(d × 0.374) + 1,457	d × 0.447
7 CV and above	d × 0.697	(d × 0.394) + 1,515	d × 0.470

d = distance covered in kilometers. For a 100% electric vehicle, these amounts are increased by 20%.

The scale has not been uprated this year: its last increase dates from 2023, by 5.4%. For 4,000 km covered with a 5 CV vehicle, it gives €2,544 of actual expenses.

Be careful what the scale covers. It is not a fuel allowance: it includes the vehicle's depreciation, repairs and maintenance, tires, insurance and fuel. Only tolls, parking and loan interest can be added, on presentation of receipts. It therefore does not replace a detailed fuel cost calculation for a company that wants to steer its fleet precisely.

Flat-rate scale or actual expenses: which to choose?

An employee using their personal vehicle for business journeys chooses, at tax return time, between the scale and the deduction of justified actual expenses. The scale is simpler and sufficient in the vast majority of cases; actual expenses only become advantageous with very intensive business use, and receipts kept all year. For a company reimbursing mileage expense claims, it is the published scale that serves as the reference, regardless of the vehicle's real consumption.

Combustion or electric: comparing energy cost on the same trip

350 km trip	Combustion (7.5 L/100 km)	Electric (18 kWh/100 km)
Consumption over the trip	26.25 L	63 kWh
Energy cost — assuming €1.80/L and €0.25/kWh on slow charging	€47.25	€15.75
Cost on public rapid charging — assuming €0.55/kWh	—	€34.65

These three prices are calculation assumptions, not recorded figures: check them at the moment of the decision. The gap favoring electric on slow charging must be weighed against the cost of charging infrastructure, downtime, and real range on long journeys.

Manual calculation or telematics?

Manual calculations remain useful for understanding the mechanism, but become impractical at fleet scale. Telematics solutions automate the collection — GPS tracking, instantaneous consumption, kilometers covered — and the calculation of cost per trip, per vehicle and per driver, while flagging the driving behavior that generates over-consumption and the maintenance needs behind it.

Five levers to reduce a fleet's fuel cost

1. Train drivers in eco-driving: anticipating braking, limiting sharp acceleration and holding a steady engine speed reduce consumption with no capital investment.

2. Check tire pressure: an underinflated tire measurably increases consumption on a long journey.

3. Optimize routes and group rounds: fewer empty kilometers, fewer avoidable detours.

4. Secure fuel cards: systematically cross-checking declared mileage against the volume purchased quickly reveals an anomaly.

5. Track consumption by driver: differences between drivers on the same model show where awareness efforts will pay off most.

How Dadycar helps calculate and reduce fuel costs

Dadycar links each fuel card to its vehicle and keeps fuel and charging histories per vehicle. On a connected vehicle or one fitted with a telematics unit, it also reports the fuel level, trips and eco-driving score, so training can be targeted. The dashboard consolidates the fleet's fuel spending, and the anomaly engine, like the fuel theft alert, surfaces the discrepancies that spreadsheet tracking only reveals months later.

Frequently asked questions

How can average consumption be calculated without a telematics unit?

Note the mileage at each fill-up and the quantity added, then apply (liters / kilometers) × 100 over several consecutive fill-ups, to smooth out variations linked to the route and to driving.

Does the mileage scale cover fuel only?

No. It is a flat rate covering the vehicle's depreciation, repairs and maintenance, tires, insurance and fuel. Tolls, parking and loan interest can be added on presentation of receipts.

Should the day's price or an average price be used?

For a budget estimate, a monthly or quarterly average, or the price negotiated with the fuel card provider. An instantaneous price fluctuates weekly and distorts comparisons between periods.

Has the 2026 mileage scale been uprated?

No. As in 2025, it has not been uprated; its last increase dates from 2023, by 5.4%.

Does the calculation change for an electric vehicle?

The formula transposes to a cost per kWh rather than a price per liter, and slow charging at the company or at home must be distinguished from public rapid charging, which is markedly more expensive. Under the mileage scale, an electric vehicle benefits from a 20% increase.

How can a mileage expense claim be verified?

By comparing the distance actually covered, recorded by telematics, against the declared mileage. It is the most reliable way to eliminate approximate estimates and systematic rounding up.