What this calculator does
The fuel cost of a trip is distance multiplied by consumption divided by a hundred, multiplied by the fuel price. Forty kilometres at 8 L/100km and $1.90 a litre is $6.08 a trip, which over five trips a week is $30.40.
Splitting that between riders is where the value is. Alone it costs $30.40 a week; with four sharing it is $7.60 each. The saving is steep at first and then flattens: the second rider halves the cost, the third takes off another third, and the fifth saves only $1.52 more than the fourth.
The formula
The cost per trip is the distance multiplied by the consumption per hundred kilometres and by the fuel price. Multiplying by trips per week gives the weekly cost, which is divided by the number of riders sharing. The annual figure assumes 48 weeks, allowing for leave. Only fuel is included, not the wider costs of running the car.
| Term | Meaning |
|---|---|
| Consumption | Litres per hundred kilometres. Lower is more efficient. |
| Cost per trip | The whole-car fuel cost of one journey, before splitting. |
| Riders | Everyone sharing the cost, including the driver. |
| 48 weeks | The annualisation basis, allowing about four weeks away from the commute. |
The inputs explained
| Field | What to enter |
|---|---|
| Round-trip distance (km) | One-way distance in kilometres, or the round trip if that is how you want to count trips. |
| Fuel consumption (L/100km) | Fuel consumption in litres per 100 km. Your own recent figure is better than the manufacturer one. |
| Fuel price ($/L) | Fuel price per litre. |
| Trips per week | Trips per week. |
| Riders sharing the cost (including driver) | Number of people sharing, including the driver. |
When to use it
Setting a fair contribution
A figure derived from actual distance, consumption and fuel price is easier to agree than a round number someone suggested.
Deciding whether carpooling is worth it
The annual per-rider figure against the inconvenience of coordinating is the real trade, and the number makes one side of it concrete.
Adding or losing a rider
The per-rider cost changes non-linearly, so the effect of one person leaving is larger in a small group than a large one.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does each rider save?
The same weekly driving split between different numbers of riders.
| Riders sharing | Cost per rider, per week | Total weekly fuel cost | Annual cost per rider (48 weeks) |
|---|---|---|---|
| 1 | $30.40 | $30.40 | $1,459.20 |
| 2 | $15.20 | $30.40 | $729.60 |
| 3 | $10.13 | $30.40 | $486.40 |
| 4 | $7.60 | $30.40 | $364.80 |
| 5 | $6.08 | $30.40 | $291.84 |
Questions
Should the driver pay a share?
Common practice varies. Splitting evenly including the driver is the simplest and is what this calculates. Some groups have passengers cover the full fuel cost in exchange for the driver providing the car, its wear and the driving itself, which is also defensible.
Does this include wear and depreciation?
No, fuel only. The full cost of running a car is typically two to four times the fuel cost once tyres, servicing, insurance and depreciation are counted. For a fair contribution to the true cost, a per-kilometre rate covering all of it is the better basis.
Does carrying passengers use more fuel?
Marginally. Extra weight affects acceleration and hill climbing more than steady cruising, and four adults might raise consumption a few percent. It is far too small to be worth adjusting the split for.
How should we handle irregular attendance?
Cost per rider per trip is the figure to use, tracking who travelled on which days rather than assuming everyone travels every day. The calculator gives that per-trip figure alongside the weekly one.
For comparing driving against public transport, see the commute comparison calculator. For a single journey, see the trip fuel cost calculator.