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U.S. domestic flights (including flights to Puerto Rico and the U.S. Virgin Islands): lap child is free, no ticket required. Can be arranged at check-in

For flights between the U.S., Canada and Mexico: ticket is required, and you pay only taxes.

International flights (including flights to Guam): ticket is required and charged a partial fare based on the destination.

Traditionally UA has used the 10% as appears below (IATA policy), some recent reports suggest UA is capping this at $250+taxes for award tickets, unclear if this applies to upgrades -- no clear posted policy


For non-domestic trips, lap-child is charged 10% price of an adult ticket for the cabin you are booked into.
If upgraded, then it is 10% of the upgraded cabin.
The price is determine at time of purchase of the lap-child ticket.

related threads: Lapchild fee not charged at booking

Traveling with lap child on international business class

archive: Lap Infant Ticket Pricing with Upgrade / Award Seat {Archive}