The break-even formula
Driving cost ≈ (miles × 2) ÷ MPG × gas price + parking. Flying cost ≈ (ticket × passengers) + bags + airport parking + rental car + rideshare. For most US routes the break-even is around 700–900 miles for couples.
When driving wins
Driving wins on cost when: traveling with 3+ people, hauling gear (bikes, ski equipment), needing a vehicle at destination, or going to a city poorly served by airlines. Use the Trip Cost Calculator for an exact estimate.