Carpooling to Work: What the Split Actually Saves, and the Detour That Eats It

Alternating drivers with one other person cuts the miles each of you drives in half. On an illustrative 12-mile commute that is $2,188.80 a year per person at the IRS rate, before the pickup detour takes part of it back. The split only holds up if you count the detour, price the miles at the same rate on both sides of the deal, and keep per-day costs separate from per-mile ones.

Every figure below is illustrative. Your distance, days, rate and fuel price are inputs, and the Commute Cost Calculator takes them. For the solo version of this arithmetic, see What Your Commute Actually Costs.

The setup, priced two ways

Take 12 miles each way, 5 days a week, 48 weeks a year. Both directions count, so that is 24 miles a day, 240 days, 5,760 miles a year.

There are two prices for those miles, and a carpool deal can use either one.

Price	Rate	Solo, per year
Energy only (illustrative $3.19 a gallon at 27 MPG)	11.8¢ a mile	$680.53
All-in (IRS standard mileage rate, July 1 – December 31, 2026)	76¢ a mile	$4,377.60

The IRS rate is a national average of the fixed and variable costs of operating a car: fuel, depreciation, insurance, maintenance and tires. It is a costing figure for an average car, not your car's actual cost.

Two people, alternating weeks

If you and one other person swap weeks, each of you drives 24 of the 48 weeks. That is 120 driving days and 2,880 miles each.

• All-in: 2,880 × 76¢ = $2,188.80 a year, against $4,377.60 solo.
• Energy only: 2,880 × 11.8¢ = $340.27 a year, against $680.53 solo.

That is the headline saving, and it assumes nobody leaves their route.

Where the split goes wrong

1. The pickup detour

Suppose collecting the other person adds 3 miles each way. The driving day becomes 15 miles each way, 30 miles a day, and your 120 driving days become 3,600 miles.

• All-in: 3,600 × 76¢ = $2,736.00 a year. The saving against solo falls from $2,188.80 to $1,641.60, a difference of $547.20.
• Energy only: 3,600 × 11.8¢ = $425.33 a year. The saving against solo is $255.20.

Three miles is small enough to leave out of a mental estimate and large enough to take about a quarter of the all-in saving. Enter the detour as part of the one-way distance.

2. Splitting at one price and bearing costs at another

Now change the arrangement: one fixed driver, one rider, 15 miles each way, all 240 days. That is 7,200 miles, $5,472.00 a year all-in and $850.67 a year in energy.

• Split evenly at the all-in rate, each person's share is $2,736.00, or $11.40 a commute day. The driver ends up where the alternating pair did.
• Split evenly at energy only, the rider pays $425.33. The driver's net cost is $5,472.00 − $425.33 = $5,046.67, which is $669.07 more than driving solo ($4,377.60).

The second deal looks fair because the rider is paying "half the gas". The driver is carrying the depreciation, insurance, maintenance and tires on 7,200 miles. Whether the energy-only split is acceptable depends on whether the driver would own and insure this car anyway. That question decides which price is yours. Agree on a price before the first ride.

3. Counting parking per person

Tolls and parking are charged per day, not per mile. At an illustrative $12 a day, a solo driver pays $12 × 240 = $2,880 a year. Alternating drivers who share one car on driving days pay it on 120 days: $12 × 120 = $1,440. That holds only if your garage charges per car. If it charges per permit, the saving is zero.

The IRS treats parking fees and tolls as sitting outside the standard mileage rate, so add them on top of the per-mile figure rather than folding them in.

4. Assuming the car costs the same with a passenger in it

An extra 100 pounds in a vehicle "could reduce your MPG by about 1%," according to the Department of Energy. The effect is small, and it is not zero. Use your own fill-up figures if you want it exact. The True MPG Calculator works out fuel economy from two odometer readings and a fill-up.

5. Assuming payments from riders change your taxes

They do not, in the ordinary case. IRS Publication 463 says: "Don't include payments you receive from the passengers in your income." It adds: "These payments are considered reimbursements of your expenses." Two limits apply. The same publication says: "You can't deduct the cost of using your car in a nonprofit car pool." And "if you operate a car pool for a profit, you must include payments from passengers in your income."

Commuting itself is not deductible either: "You can't deduct commuting expenses no matter how far your home is from your regular place of work." The IRS rate in this guide is used to price the drive, not to claim it.

Putting it into the calculator

Run the calculator once per arrangement.

• Alternating weeks: one-way miles including the detour, 5 days, and 24 weeks (your driving weeks).
• Fixed driver: one-way miles including every pickup, 5 days, 48 weeks, then divide the result by the number of people in the car.
• Parking and tolls: enter them in the per-day field, on driving days only.

Run each at both the energy rate and the all-in rate. If the arrangement works at the price you are actually bearing, the argument is over. If a trip with several passengers matters more than a commute, the Trip Fuel Cost Calculator splits a single drive across everyone in the car.

Where this stops

Both rates are averages. The energy price depends on your real fuel economy, not the sticker, and the all-in price depends on your real car. This covers money only, not the time a pickup adds to your morning.

This is arithmetic, not advice, and it is not tax advice. Informational only, not professional advice.

Last reviewed: October 2026.