About the Gas Split Calculator
This gas split calculator divides the fuel cost of a road trip or carpool between the people in the car. List each person with the distance they rode, enter the car's fuel economy and the fuel price, and it works out the total gas cost and exactly what each rider owes. Tolls, parking and other shared costs can be added and split equally.
The default "shared legs" method treats the trip as a series of legs: everyone leaves from the same place and riders are dropped off along the way. The cost of each leg is split equally among the people still in the car, so someone who rides only the first 80 miles pays a share of those 80 miles and nothing more. The simpler "proportional" method splits the total fuel cost in proportion to each person's distance.
It suits friends on a road trip, carpools to work or events, and group holidays where people join or leave partway. Include the driver in the list if the driver shares the cost; leave them out if the passengers are covering the fuel.
With the default inputs, the total trip cost (fuel + extras) is $37.50. Change any value above to recalculate instantly.
How to use the gas split calculator
- 1List each person on a new line with the distance they rode, e.g. "Sam, 120".
- 2Include the driver if they share the cost.
- 3Enter the car’s fuel economy and the price paid for fuel.
- 4Add tolls, parking or other costs everyone shares.
- 5Pick a split method and read what each person owes in the table.
Formula and method
The fuel cost per mile is the fuel price divided by fuel economy, and the car's distance is the longest distance anyone rode, so total fuel cost is that distance times the cost per mile. With the shared-legs method the trip is cut at every drop-off point; the cost of each stretch is divided equally among the riders still in the car, and each person's share is the sum of their stretches.
The proportional method instead multiplies the total fuel cost by each rider's distance divided by the sum of all riders' distances. Shared extras such as tolls and parking are divided equally among everyone listed. Both methods assume everyone starts at the same point.
- D
- Distance the car drove (longest rider distance)
- price
- Fuel price per gallon (or litre)
- mpg
- Fuel economy in distance per gallon (or litre)
- share_i
- Fuel cost owed by rider i
Worked examples
Four friends, two dropped off early
At 28 mpg and $3.50 a gallon, gas costs $0.125 per mile, so the 300-mile trip costs $37.50. The first 80 miles ($10) are split four ways ($2.50), the next 70 ($8.75) three ways and the last 150 ($18.75) two ways, so Priya pays $2.50, Jordan $5.42 and Alex and Sam $14.79 each.
Proportional split with tolls
The car drives 200 miles at $0.16 per mile, so fuel is $32. Distances sum to 500, so Ana and Ben each pay 200/500 × $32 = $12.80 and Cara pays $6.40; the $18 of tolls adds $6 each, making $18.80 and $12.40.
Equal carpool to a festival
Everyone rides the whole 180 miles, so the $18 of fuel (180 ÷ 32 × $3.20) splits evenly: $6 per person.
Frequently asked questions
What is the fairest way to split gas money?+
Splitting each stretch of road among the people in the car for that stretch is usually seen as fairest, because nobody pays for miles they did not ride and everyone shares the cost of the car being on the road.
Should the driver pay a share of the gas?+
That is up to the group. On shared trips the driver often pays an equal share; in carpools where the driver provides the car, passengers sometimes cover all the fuel to compensate for wear, insurance and depreciation.
How do I calculate the gas cost of a trip?+
Divide the distance by the car’s fuel economy to get gallons used, then multiply by the price per gallon. For example, 300 miles at 30 mpg uses 10 gallons, which costs $35 at $3.50 a gallon.
Can I use kilometres and litres?+
Yes. Enter rider distances in kilometres, fuel economy in km per litre and the price per litre. The maths is identical as long as all three use the same units.
Does this include wear and tear?+
No, it covers fuel plus any shared extras you enter. To include vehicle running costs, add them as a shared extra or use a per-mile rate such as the IRS mileage rate instead of fuel cost.