A traveler can view his United Airlines seating assignment on his boarding pass or by looking up the reservation at United.com after purchasing the ticket. In some instances, passengers may receive seat assignments at check-in or at the gate prior to departure.
A passenger can choose his seat assignment during ticket purchase or online following the ticket purchase. He can change his seat assignments during check-in. In some instances, a passenger can request seat assignment changes or upgrades at the departure gate.
Regardless of the airfare class a passenger purchases, United does not guarantee seat assignments. The airline may cancel a passenger's seat assignment if he does not check in on time.