Frontier Airlines does not count seat assignments along the booking value. So one may purchase the seat either while booking or after reservations. Or else, the customers can appeal Frontier Airlines Seat Selection during the check-in online window accessibility. 

One might have to pay for seat selection in advance, until or unless someone has the membership in bundles, the WORKS BET or the PERKS  ́. If someone does not select the seat in advance rather than 24 hours before departure when the check-in online window is open they are liable for free seat selection which varies the seat accessibility. 

Furthermore, frontier airlines assign the random seats to the customers if they do not choose the seats in advance.

When Can I Appeal for Frontier Airlines Seat Selection?

However, one has the potential to choose the seat in advance or during flight reservation. But one must pay for the seat selection in advance until or unless they have membership in bundles, the WORKS BET or the PERKS. To prevent the seat selection fee, you can purchase the seat when Frontier Airlines Check-in window is open. The Check-in window is open for 24 hours before the scheduled departure and it gets closed one hour earlier the departure.

How Much Fee Does Frontier Airlines Charge for Seat Selection?

However, it's tricky to give you the actual sum of Seat Selection. Still, if you want to seek better suggestions about Seat Selection Fee so that you would prepare your budget accordingly. The Frontier Airlines fee for seat selection varies route and fare type, from $17 to $55 per way for standard economy fare. According to the analysis, you can have an estimation of an average of $36 for pre seat selection on a roundtrip flight.