In short: A carpool cost per person is the day's fuel (miles divided by miles per gallon, times the price of a gallon) plus tolls and parking, divided by the people sharing. A 36 mile round trip at 30 mpg and $3.40 a gallon, with $14.00 of tolls and parking, costs $18.08, or $6.03 each for three people.
How to use the carpool cost calculator
- Enter the trip. Type the distance one way and leave Round trip ticked for a commute there and back. Add the price you pay for fuel, and the tolls and parking for one day.
- List the people in the car. Choose how many ride, name them, and give each the days they drive in a week and their own car's miles per gallon. Somebody who never drives gets 0 days and needs no car.
- Choose who shares the cost. Everyone, driver included, suits a commute that all of you would make anyway. The passengers only suits a favour, where the riders cover the driver's costs.
- Read the shares and the payments. The result shows each person's fair share for a week, a month or a year, what each driver pays out at the pump and the toll booth, and the payments that settle the difference.
Everything updates as you type and nothing leaves your browser. Copy the result as text for the group chat, or copy a share link that opens the same figures for the others to check.
How a carpool cost is worked out
There are three parts to one day's drive. Fuel is the distance divided by the car's miles per gallon, times the price of a gallon: 36 miles / 30 mpg = 1.2 gallons, and 1.2 x $3.40 = $4.08. Tolls and parking are what the driver pays that day, here $4.00 and $10.00. An optional amount per mile covers tires, oil and repairs. Together the day in Alex's car costs $18.08, which is $6.03 per person for three. The same day in Sam's car, at 22 mpg, burns 1.64 gallons and costs $19.56.
The car's fuel economy changes the day's cost a good deal, which is the reason to split gas by the car that actually made the trip. Fuel for the example's 36 mile round trip at $3.40 a gallon:
| Fuel economy | Fuel used | Fuel cost | Each of 2 | Each of 3 | Each of 4 |
|---|---|---|---|---|---|
| 20 mpg | 1.8 gal | $6.12 | $3.06 | $2.04 | $1.53 |
| 25 mpg | 1.44 gal | $4.90 | $2.45 | $1.63 | $1.23 |
| 30 mpg | 1.2 gal | $4.08 | $2.04 | $1.36 | $1.02 |
| 35 mpg | 1.03 gal | $3.50 | $1.75 | $1.17 | $0.88 |
| 40 mpg | 0.9 gal | $3.06 | $1.53 | $1.02 | $0.77 |
| 50 mpg | 0.72 gal | $2.45 | $1.23 | $0.82 | $0.61 |
A week is the days driven times the day's cost, a month is counted as a twelfth of 52 weeks (about 4.33 weeks) and a year as 52 weeks, so take out any weeks the carpool does not run. Shares are rounded to the cent in a way that always adds up to the total.
How to split carpool costs when you take turns driving
A plain fuel calculator stops at one car and one driver. When a carpool rotates, the cars do not cost the same to run and one person may drive more often than the rest. The fair way to settle it has three steps: add up what each driver pays out on their own driving days, divide the total by the people in the carpool to get each person's fair share, and have the people who paid out less than their share pay the ones who paid out more.
In the example, Alex drives three days a week in a 30 mpg car and Sam drives two days in a 22 mpg car, and Jo does not drive. Alex pays out 3 x $18.08 = $54.24 a week and Sam 2 x $19.56 = $39.12, so the carpool costs $93.36 a week and each person's fair share is $31.12.
| Person | Days driving | Pays out | Fair share | Balance | Driving alone | Saves |
|---|---|---|---|---|---|---|
| Alex | 3 | $54.24 | $31.12 | is owed $23.12 | $90.40 | $59.28 |
| Sam | 2 | $39.12 | $31.12 | is owed $8.00 | $97.80 | $66.68 |
| Jo | 0 | $0.00 | $31.12 | owes $31.12 | no car entered | no car entered |
Jo owes the whole share, and pays $23.12 to Alex and $8.00 to Sam, which leaves all three having paid $31.12. Over a month that is $100.18 and $34.67. If you take turns driving evenly you can often skip the sums, because it nearly evens out: two people who each drive half the week in these two cars settle the month with one payment of only $8.02. The sums matter when one person drives more, or when somebody never drives.
Gas money: how much to give the driver
When one person always drives, the question becomes how much gas money the riders should hand over. With Alex driving all five days, the week costs $90.40. Shared by everyone, driver included, each passenger owes $30.13 a week. If the passengers only split gas, tolls and parking between them, each owes $45.20. Neither is wrong; the first treats the driver as a commuter who would make the trip anyway, the second as someone doing the others a favour. If you are wondering what to pay someone for carpool rides, start from the first figure and agree anything more openly.
Fuel is not the whole cost of the miles. The always-driver's car also takes the tires, oil changes and repairs, and the Wear box adds an amount per mile for them. For a sense of scale, the IRS standard mileage rate for business driving is 76 cents a mile from July 1 to December 31, 2026 (72.5 cents for the first half of the year). It stands in for the actual expenses of running a car, which the IRS lists in Topic 510 as gas, oil, repairs, tires, insurance, registration fees, licenses and depreciation, with parking fees and tolls counted separately. At that rate the example's 36 miles would be $27.36 a day before tolls and parking, against $4.08 for fuel alone, which is 11.3 cents a mile. The IRS rate is a tax figure for business use, not a rule for friends, and insurance and registration are paid whether or not anyone rides along; sharing fuel, tolls and parking, with at most a few cents a mile on top, is the simpler agreement.
The other side of the sum is the carpool savings. Driving alone, Alex would pay for all five days: $90.40 a week, against a fair share of $31.12 in the carpool. That is $59.28 a week and $3,082.56 over 52 weeks. The Driving alone and Saves columns show it for everyone whose car you enter.
Which miles per gallon and fuel price to use
Use what the car really gets on this trip if you know it: the trip computer's average, or miles driven divided by gallons at the last fill-up. Otherwise the official ratings are a fair stand-in, and you can look up any model on the government's Find and Compare Cars page at fueleconomy.gov. A commute on open highway is closer to the highway rating and stop-and-go traffic to the city rating; the combined figure on the window sticker mixes them:
Combined fuel economy is a weighted average of City and Highway MPG values that is calculated by weighting the City value by 55% and the Highway value by 45%.
For the price, use what you pay at your usual station. To plan ahead, the Energy Information Administration's Gasoline and Diesel Fuel Update gives retail prices by region and is released every week. Diesel cars work the same way with the diesel price. For a one-off road trip with hotels and meals as well as fuel, add the fuel from here to the group expense splitter, which settles everything in the fewest payments.
Esta calculadora también está en español: dividir la gasolina de un viaje compartido, en millas, galones y dólares.
Questions people ask
How do you calculate carpool cost per person?
Divide the day's miles by the car's miles per gallon, multiply by the price of a gallon, add the day's tolls and parking, and divide by the people sharing. A 36 mile round trip at 30 mpg uses 1.2 gallons, $4.08 at $3.40 a gallon; with $4.00 in tolls and $10.00 for parking the day costs $18.08, or $6.03 each for three people.
How do you split gas money when you take turns driving?
Add up what each driver spends in a week on their own driving days, divide the total by the people in the carpool to get the fair share, and compare. Whoever spent more than the share is owed the difference by whoever spent less. In the page's example, Jo never drives and owes $31.12 a week: $23.12 to Alex and $8.00 to Sam.
How much should you pay someone for carpool rides?
An equal share of what the trip costs the driver in fuel, tolls and parking is a fair starting point: in the example, $6.03 a day each when three people share Alex's car, the driver included. If the passengers cover the whole cost between them it is $9.04 a day each. Add a few cents a mile for wear if the same person always drives.
Should the driver pay a share of the carpool cost?
It depends on the trip. When the driver is going there anyway, as on a commute, it is fair for the driver to pay a share like everyone else, and choosing Everyone, driver included does that. When the driver is doing the others a favour, or is putting all the miles on their own car, the group may agree that the passengers only cover the cost; the calculator shows both.
What about a rider who joins part of the way?
The calculator treats everyone as riding the whole distance, which fits a commute where everyone is picked up near the start. For someone who rides only part of the route, work out the shares for the full group first, then agree a smaller share for that rider in proportion to the miles they are in the car, and spread the difference over the others.
Does the calculator work in kilometres and litres?
Yes. Choose Kilometres and litres and enter the distance in kilometres, each car's fuel use in litres per 100 km and the price per litre. A 60 km round trip at 7.5 litres per 100 km uses 4.5 litres, $7.20 at $1.60 a litre, or $2.40 each for three people. Nothing is converted for you when you switch, so retype the figures in the new units. As a guide, 30 miles per US gallon is 7.84 litres per 100 km.
Is anything I type sent anywhere?
No. The calculator runs in your browser. Copy share link puts your figures and names in the part of the address after the #, which browsers never send to a server, so only the people you give the link to see them.