How to split fuel costs on a road trip with friends (and what each person pays)

The short answer

• If you all make the whole trip, split the total evenly, counting the driver too.
• If someone gets in or out along the way, split by stretches: each stretch is paid by whoever is in the car for it.
• Each extra person adds little to the total (about €0.75 over 400 km, from the weight), but cuts each person’s share a lot.
• Sharing costs is legal; charging more than the trip costs to make a profit is not.

What each person pays: a 400 km trip

We take a trip of 200 km (124 miles) each way, mostly on dual carriageways, in the petrol hatchback from our guides (6.0 L/100 km WLTP). The calculator adds 75 kg (165 lb) for each passenger; more weight means more fuel, especially when accelerating. According to fueleconomy.gov, an extra 100 lb (45 kg) cuts efficiency by about 1%.

Luggage counts too. With four people and the boot packed for a holiday (about 150 kg), the trip costs about €1.50 more. A roof box matters far more, because of air resistance: see roof boxes and luggage. In practice, weight barely changes the split: what decides how much each person pays is how many of you there are.

When you don’t all make the same trip

If someone gets out early or joins along the way, an even split isn’t fair. The simplest approach is to break the trip into stretches and split each one between the people in the car. For that you need the cost per km, which the calculator gives you.

An example with the same car: 300 km (186 miles) one way between 4, and one person gets out at km 200. Fuel works out at about €0.13/km, €38.38 in total.

• First stretch (200 km), between 4: €6.40 each. That’s what the person who gets out pays.
• Second stretch (100 km), between 3: the others pay €10.66 each in total.
• With an even split, everyone would pay €9.60.

Detours work the same way: if the driver goes 20 km out of the way to pick someone up, that person pays for those km, or you share them if it’s not much. Tolls and parking are split between those who go through them.

Sharing costs, yes; making a profit, no

Giving friends a lift and sharing what the trip costs is private transport. In Spain, the Land Transport Act (art. 101) says private transport can’t involve “direct or indirect monetary payment”, other than travel expenses. In other words, you can charge what the trip costs, but not make money from it, because then it becomes an unlicensed transport service.

In 2017, a Madrid commercial court ruled for BlaBlaCar against the coach operators’ association: it found that the platform puts private individuals who share costs in touch, that this is private transport and that there is no profit motive. Users were paying between €0.06/km and €0.09/km.

What about wear on the car? Fuel isn’t the only cost of using it: tyres, oil, servicing and insurance add up too. As a reference, the Spanish tax authority exempts up to €0.26/km from income tax when an employer pays a worker to use their own car (Order HFP/792/2023), almost twice the fuel cost in our example (€0.12/km). Among friends, the usual approach is to split just the fuel and tolls, and for passengers to treat the driver to something.

Tips

• Agree on the split before you set off: whether the driver pays, what happens with tolls and how you’ll pay.
• Work out the cost beforehand with the calculator: tick “Return”, set “Number of travellers” to how many of you there are, driver included, and it gives you the “Cost per person”.
• If you want the exact figure, fill the tank when you leave and when you get back: the second fill-up is the fuel for the trip. How to measure it: work out your real mpg.
• To spend less, drive at 110 km/h instead of 120: see fuel consumption by motorway speed.
• If you share a car to work every day, use the commuting fuel cost calculator.

Frequently asked questions