Do airlines overbook every flight?

Most major airlines overbook some flights, but not all of them. Overbooking is the practice of selling more tickets than seats, betting that some passengers won't show up (historically, 5-15% of ticketed passengers are no-shows depending on route and fare class). Airlines use sophisticated predictive models to determine how much to overbook each specific flight.

Flights most likely to be overbooked: business routes on Monday mornings and Friday evenings (flexible-ticket passengers who frequently change plans), high-demand holiday flights, and routes with a history of high no-show rates. Flights least likely to be overbooked: leisure routes to vacation destinations, red-eye flights, and routes where the airline has recently had involuntary denied boardings.

When overbooking goes wrong and too many passengers show up, the airline first asks for volunteers (with vouchers or cash as incentive). If not enough people volunteer, they involuntarily deny boarding — and federal law kicks in: cash compensation of 200-400% of your one-way fare (up to $1,550), plus rebooking. In practice, involuntary denied boarding is rare — about 0.26 per 10,000 passengers across the industry. Your best protection: check in online as early as possible (24 hours before), get a seat assignment, and arrive at the gate early.