How the comparison works
Fuel uses the same maths as our fuel cost calculator, in the units of the country you pick. If you set a value for an hour of your time, each option also gets hours × travellers × value per hour added.
Why group size matters so much
Driving costs are mostly per car: the fuel bill is the same whether one or four people are inside. Flying costs are mostly per person. That's why the calculator searches for the break-even group size — the smallest number of travellers at which driving costs the same as flying or less. It assumes everyone fits in one vehicle.
Worked example
Two people make a 500-mile trip each way (1,000 miles) in a 25 mpg car with gas at $3.50: fuel is 1,000 ÷ 25 × 3.50 = $140. Add $20 of tolls and driving costs $160. Flying at $250 each plus $40 airport parking and $100 of taxis comes to $640. Driving saves $480 — before counting time.
For more examples, including how the value of your time can change the answer, read is it cheaper to drive or fly?
Hidden costs worth including
- Wear and tear: tyres, servicing and depreciation build up with every mile. Even a small per-mile figure adds up over a long trip.
- Overnight stops: long drives often need a hotel night each way, which can tip the balance.
- Bag fees and seat selection: budget fares can look cheap until bags are added.
- Getting around at the destination: with a car you already have transport; without one you may need car hire or taxis.
- Time: door-to-door flying time includes getting to the airport, security and transfers — often much longer than the flight itself.