In 2026, valid reasons for complimentary (involuntary) rebooking include flight cancellations by the airline, schedule changes of more than two hours, or missed connections caused by a delay of an earlier flight on the same itinerary. Airlines are also required to offer rebooking if they "downgrade" your service class or change your arrival/departure airport. For voluntary rebooking, valid reasons that often waive fees include sudden illness (with a doctor's note), "Force Majeure" events like natural disasters or civil unrest at the destination, or significant personal emergencies. Under 2026 passenger rights regulations (like the updated DOT rules in the U.S.), if an airline significantly changes your flight time, you are entitled to a rebooking on the next available flight or a full refund. However, "change of plans" or "found a better price" are generally not valid for free rebooking and will require you to pay the fare difference and any applicable change fees.