Carpooling Calculator for daily commutes. It splits each round trip among the people in the car, prices each mile with gas, AAA wear costs or the IRS rate, and adds pickup detours.
Count everyone in the car, driver included. Use your real round trip, home to work and back, before any pickup detour.
Schedule, Tolls and Fair Split
Gas alone undercounts what the car costs to run. AAA puts 2026 maintenance, repair and tires at 11.7¢ a mile, and the IRS 2026 business rate adds insurance and depreciation.
Savings by Carpool Size
| Carpool | Share per Day | Saved per Person a Year | Cheaper By |
|---|---|---|---|
| 2 people | $5.13 | $1,007 | 45% |
| 3 people | $3.42 | $1,417 | 63% |
| 4 people | $2.56 | $1,622 | 73% |
| 5 people | $2.05 | $1,745 | 78% |
| 6 people | $1.71 | $1,827 | 82% |
| 7 people | $1.47 | $1,886 | 84% |
Split a Commute With the Carpooling Calculator
The Carpooling Calculator works out what each person pays when several commuters share one car to work. It compares that share with what each would pay driving alone, then adds the gas, CO₂ and miles the group keeps off the road.
Coworkers use it to agree on a fair weekly amount before the first ride. Drivers use it to check whether the riders’ money actually covers the car, not just the gas. All inputs are US units: miles, MPG, dollars per gallon and pounds of CO₂.
Three Ways to Price a Mile
Most carpool tools split gas and stop there. This one lets you choose what a mile of driving costs, and that choice moves the dollar figures more than any other input.
Gas Only divides the gas price by the car’s MPG. At $3.25 a gallon and 28 MPG, that comes to 11.6¢ a mile.
$$c = \frac{P}{\text{MPG}}$$
In this formula, c is the cost per mile and P is the gas price in dollars per gallon.
Gas Plus Wear adds 11.7¢ a mile for maintenance, repairs and tires. That figure comes from AAA’s 2026 Your Driving Costs study, averaged over five years and 75,000 miles. These are the costs that grow with every mile, so the driver is not quietly paying for brakes and tires.
The IRS rate prices the whole car at 76¢ a mile, which includes gas, wear, insurance and depreciation. The IRS raised its 2026 business rate from 72.5¢ to 76¢ on July 1 because fuel costs climbed. Even 76¢ sits below AAA’s 2026 full-cost average of 86¢ a mile for a new car driven 15,000 miles a year.
How Your Daily Share Is Worked Out
The tool first prices a solo commute, which is your round trip times the cost per mile plus any daily tolls and parking.
$$S = D \times c + T$$
In this formula, D is the round-trip distance in miles and T is tolls and parking per day. With the defaults of 40 miles in the gas-plus-wear mode, one solo day costs $9.32.
The carpool car drives the same trip plus the pickup detour. The group splits that day’s cost evenly when everyone takes turns driving.
$$s = \frac{(D + d) \times c + T}{n}$$
In this formula, d is the daily detour in miles and n is everyone in the car, driver included. Three people with a 4-mile detour pay $3.42 each per day. Over 240 commute days, that saves each person $1,417 compared with driving alone.
Enter the round trip, not the one-way distance. Several competing calculators ask for one-way miles and double them. Typing a one-way figure here cuts every result in half.
The “One Driver Rides Free” option divides the car’s cost by the riders only, using n − 1. The driver pays nothing and gets a weekly total back for lending the car.
Why the Percentage Barely Moves
The “Cheaper Than Driving Alone” figure behaves differently from the dollar figures. When tolls are zero, the cost per mile cancels out, so the percentage depends only on the group size and the detour.
$$\text{Saved} = 1 – \frac{D + d}{n \times D}$$
That is why the default commute shows 63% cheaper in all three pricing modes. Only the dollar amounts change between them. Tolls and parking break this pattern slightly, because they are the same whether one person drives or four.
When a Pickup Detour Cancels the Savings
Each pickup adds miles to the shared car, and those miles are split too. When everyone takes turns, the savings reach zero once the detour equals the round trip times (n − 1).
A two-person carpool on a 40-mile commute breaks even at a 40-mile detour. A four-person group breaks even at 120 miles, which is exactly the tool’s upper limit. The tool rejects any detour above three times the trip.
The one-driver setup is less forgiving. Two people with any detour at all means the lone rider pays more than their own solo commute. The tool warns about this and suggests the driver pay a share or the group add a rider.
Other input limits come straight from the tool. It accepts 2 to 15 people in whole numbers, 1 to 7 days a week, up to 52 weeks a year and gas up to $20 a gallon.
Gas, CO₂ and Miles Kept Off Your Car
The gas saved is the miles everyone would have driven alone, minus the carpool car’s miles, divided by MPG. The tool uses the same MPG for every solo car, so a group that normally drives trucks saves more gas than it shows.
Each gallon of gasoline burned releases 8,887 grams of CO₂, or about 19.6 lb, according to the EPA. The default three-person carpool avoids 651 gallons and about 12,761 lb of CO₂ a year, even after the detour miles are taken out.
When everyone rotates, each car loses 6,080 miles a year at the defaults. At AAA’s 11.7¢ a mile, that is about $711 of maintenance and tires avoided. Fewer miles also slow depreciation, which the Used Car Value Calculator shows when you compare mileage at trade-in.
The table below prices the same default commute in all three modes: 40 miles, 3 people, 28 MPG, $3.25 gas and a 4-mile detour. It shows how much the basis you choose changes what each person owes.
| What the Split Covers | Cost per Mile | Share per Day | Saved per Person a Year |
|---|---|---|---|
| Gas only | 11.6¢ | $1.70 | $706 |
| Gas plus AAA wear | 23.3¢ | $3.42 | $1,417 |
| IRS 2026 rate | 76¢ | $11.15 | $4,621 |
Carpooling Calculator Inputs People Get Wrong
Leaving the driver out of the head count is the most common slip. “People in the Carpool” means everyone in the car. Entering 2 for a driver and two riders overstates each share by half.
The second slip is adding the pickup detour into the round-trip field. Round-Trip Commute is your own home-to-work-and-back distance. The detour has its own field, so entering it twice inflates both the solo cost and the savings.
The third is using 52 work weeks. Holidays, vacation and sick days cut that down, which is why the Contra Costa 511 carpool calculator assumes 50 weeks and the tool defaults to 48. At 52 weeks, a year’s savings run about 8% high.
Paying the Driver Fairly
How much should I charge a coworker to carpool?
Start with the gas-plus-wear share for the days they ride. At $3.25 gas, 28 MPG and a 40-mile round trip, that is $3.42 a day each for three people, or about $17 a week.
If you do all the driving, switch to “One Driver Rides Free” so the riders split the whole car. When their homes sit at different distances from work, the cleanest fix is a shared meeting point on your route. That keeps the detour field near zero and the split even.
Is splitting just the gas fair to the driver?
For casual rides, a gas-only split is the norm. For a daily carpool with one driver, it leaves out tires, brakes and oil, and AAA prices those at 11.7¢ a mile in 2026.
At the defaults, a gas-only split with one driver costs that driver about 11,000 miles of wear a year. The tool flags this case and shows how much more each rider would pay per week to cover it.
Can a carpool use the IRS mileage rate?
It can be used as a pricing basis, and many long-term carpools do. The 76¢ rate is a fair full-cost figure, because it builds in insurance and depreciation that gas-only and AAA-wear splits leave out.
It is not a tax deduction for the ride to work. As the NATP notes, commuting between home and a regular workplace is not deductible. For 2026, miles driven before July 1 are rated at 72.5¢ and miles from July 1 on at 76¢.
How much of my budget does a carpool actually free up?
The yearly figure in the hero is money that stays in your pocket each year. It does not shrink a car payment or insurance you still owe.
To see whether the car itself still fits your income, run it through the 20/4/10 Rule Calculator. A carpool that saves $1,400 a year covers roughly one month of a typical car payment.