How to Split Carpool Costs Fairly

Agree the rate. Gas money alone (gas price ÷ mpg) is the lowest. The IRS business rate covers the whole cost of the car and is the most common "fair" number. A flat rate in between is fine too — agree it before the first trip.

Agree the split. Per child is fairest when families send different numbers of children; per family is simpler. Include the driver's own children in the riders — their share is netted against the trip they drove.

Settle with the fewest payments. Add up what each family's drives are worth and subtract their share of all trips. The families with a negative balance pay those with a positive one; matching the largest debtor with the largest creditor settles four families in at most three payments.

Last reviewed 2026-11-04. General information, not tax or legal advice.