Trip cost planning

The three mistakes

Using the brochure economy figure. Manufacturer WLTP ratings are measured under laboratory conditions. Real-world consumption typically runs 10–20% above them, and further above on short trips, in hills, with a roof box, or with the air-conditioning working hard. Your own litres-per-100km, measured across a few full-tank fills, is the only figure worth planning from.

Forgetting the return leg. Mapping apps quote one-way distance. Unless you are being collected at the other end, double it before you cost it — and if there is a detour to a fuel stop or an airport drop-off, add that too.

Using a remembered fuel price. Australian pump prices moved unusually far in 2026 because fuel excise was cut in April and fully restored in August. A price you remember from earlier in the year is not close. Current five-city averages are on the fuel price data page.

What common trips cost

Fuel only, at the five-city average unleaded price of 200.7 cpl, for a car using 8.0 L/100km. Return distances.

The last column is the one that decides most drive-versus-fly arguments. Fuel is a per-vehicle cost, not a per-person one, so a full car is roughly four times cheaper per head than a solo driver — and that is usually enough to beat four airfares even before you count airport transfers and checked bags.

Drive or fly

The comparison is not fare against fuel. A fair comparison puts the full door-to-door cost of each option side by side.

Indicative Australian figures for a family trip; substitute your own. The point is the pattern — the items missing from a naive comparison usually favour driving for groups and flying for solo travellers.

Time is the term people weigh least consistently. A 900 km drive is roughly ten hours door to door; the flight equivalent is around four once you include getting to the airport, security and collecting bags. Whether the six-hour difference is worth several hundred dollars depends entirely on the trip — but it should be a stated assumption, not an unexamined one.

Splitting a carpool without an argument

The defensible basis is cost per passenger-kilometre: total trip fuel divided among the people actually in the car for each leg. Someone joining halfway pays for half the distance, not half the trip. Whether the driver pays a share is a social question rather than an arithmetic one — the common conventions are an equal split including the driver, or an equal split of fuel with the driver absorbing wear and tolls.

For a recurring carpool it is worth agreeing the rule once, in writing, at the current fuel price and revisiting it when the price moves more than about 10%. That single decision prevents most of the friction.

Refuelling on the route

Regional prices run consistently above capital-city ones — on 19 August 2026 the regional aggregate was 208.7 cpl against 200.7 cpl in the five largest cities. On a long trip, filling at the last metropolitan site before you leave and again on the metropolitan fringe on the way back is worth real money for no detour.

The spread within a single city is wider still than the gap between cities, so a state fuel app is worth a minute before you set off.

Related sections

Towing a van on the trip changes the maths substantially — see towing and caravans. For per-vehicle annual costs rather than per-trip, see vehicle running costs. Longer guides: petrol cost per km and reducing commute fuel costs.