Although Frontier will provide adjacent seats if available at the time of booking, Frontier might not provide seat assignments right away. Frontier will provide the customer the adjacent seating assignments no later than the day before scheduled departure of the flight.

Frontier Airlines does not guarantee that groups will sit together unless you pay for seat assignments at the time of booking. Because Frontier is an ultra-low-cost carrier, they use random seat assignment at check-in to encourage passengers to pay the extra $15–$50 fee for specific seats. However, as of 2026, Frontier adheres to a fee-free family seating policy: if you are traveling with a child aged 13 or younger, Frontier will guarantee that at least one accompanying adult is seated next to the child at no additional cost, provided there is adjacent availability at the time of booking. If you are a group of adults or traveling with older teens and want to ensure you are in the same row, your best bet is to purchase a "Bundle" (like the Economy or Premium bundle) which includes seat selection, as relying on the "random" algorithm during the 24-hour check-in window frequently results in being scattered across the cabin.