Spirit Airlines operates on an "unbundled" model, meaning seat selection is never free unless you wait for an automatic assignment at check-in. In 2026, the cost to choose a "standard" seat during booking typically ranges from $5 to $50 per flight leg, depending on the length of the flight and the desirability of the seat (e.g., aisle vs. middle). If you want more comfort, Spirit offers the "Big Front Seat," which features much more legroom and wider leather seating; this can cost anywhere from $50 to $250 extra depending on demand and the time of purchase. For families, Spirit's current policy aims to seat at least one adult with children under 13 for free if seats are available, but to be 100% certain you are together, paying for selection is required. It is almost always cheaper to select your seat during the initial booking on the website than it is to wait until you are at the airport counter, where prices can double.