Carpool cost calculator: gas, tolls and wear per rider

When to use this calculator

Use it for a regular commute: one person drives, the others ride along on the same days, and the group wants a monthly number for each rider. For a one-off trip, use the road trip gas cost calculator. Rates, rotating drivers and skipped days are covered in how to split carpool costs.

How the calculator works

1. Double the one-way miles to get the miles per round trip.
2. Fuel per round trip is those miles ÷ miles per gallon × the gas price.
3. Wear per round trip is those miles × the cents per mile ÷ 100. Leave it at 0 to skip it.
4. Add tolls and parking. That is the cost per round trip.
5. Multiply by the round trips in a month, then divide by the riders plus one. The driver pays a share too.

The driver’s saving is the month’s cost minus the driver’s own share. Shares are in whole cents and add up to the total, so one person may pay a cent more.

A worked example

Say the group drives 22 miles each way, 20 days a month, in a car that gets 30 MPG, with gas at $3.50 a gallon and $4 of parking per round trip. There are three riders and the driver.

• The round trip is 2 × 22 = 44 miles.
• Fuel is 44 ÷ 30 × $3.50 = $5.13.
• Adding $4 of parking makes $9.13 per round trip, or $2.28 each among four people (the exact figure is $2.2825).
• Twenty round trips cost $9.13 × 20 = $182.60 a month, so each rider pays $182.60 ÷ 4 = $45.65.
• The driver pays $45.65 too, so the driver saves $182.60 minus $45.65 = $136.95.

Wear and tear changes the result. AAA’s 2026 study puts maintenance, repair and tires at 11.7 cents a mile on average for a new car. Entering 11.7 adds 44 × $0.117 = $5.15 per round trip, so a trip costs $14.28 and each rider pays $71.40 a month.

What the number of riders changes

Each added rider lowers every rider’s share and raises the driver’s saving. These figures use the same $182.60 month.

Riders	Each rider pays a month	Driver saves a month
1	$91.30	$91.30
2	$60.87	$121.74
3	$45.65	$136.95
4	$36.52	$146.08

How the cost compares with AAA’s cost per mile

AAA’s cost per mile is far higher than a fuel and parking split, because it counts owning the car. AAA’s Your Driving Costs 2026, released on September 15, 2026, puts the average cost of owning and operating a new car at $12,863 a year. Its cost per mile falls as the miles go up: $1.10 at 10,000 miles a year, 86 cents at 15,000 and 74 cents at 20,000. Over the 44-mile round trip:

Miles driven per year	AAA average cost per mile	A 44-mile round trip
10,000	$1.10	$48.40
15,000	$0.86	$37.84
20,000	$0.74	$32.56

AAA’s figure includes depreciation, finance charges, insurance, license, registration and taxes, as well as fuel and maintenance, repair and tires. At 86 cents a mile, the example’s 880 miles a month would cost $756.80, against $182.60 for fuel and parking. Insurance and finance charges are owed whether or not anyone rides along, so decide as a group whether to count any of them.

Common mistakes

• Dividing by the riders only. Splitting $182.60 three ways charges each rider $60.87 instead of $45.65. The driver is the fourth share.
• Keeping the example gas price. The calculator opens with $3.50 as an example. The U.S. Energy Information Administration reported $4.354 a gallon for regular gasoline for the week of October 5, 2026, taxes included. At $4.35 each rider in the example pays $51.90 a month.
• Counting days nobody rode. Enter only the days the group drives together.

The driver can keep the count in EvenOut: add the month’s cost as an expense they paid, split equally among everyone in the car, and set it to repeat monthly. Each rider’s balance shows what they owe, and Settle up records the payment without moving money. If two people share the car itself, see sharing a car with a friend.