Why Frontier and Allegiant Bag Fees Change Every Time You Search

Unlike legacy carriers, where a checked bag costs one flat number regardless of route, Frontier and Allegiant price bags dynamically by route and date, the same way they price the ticket itself.

What that looks like in practice. Live quotes from Frontier's own bag calculator across two test routes showed a first checked bag ranging $65–69 online, and a second bag $69–79, same airline, different number depending on the route. Allegiant works the same way: one tested route priced a checked bag at $49 online, and the airline's own calculator explicitly allows for a wider range by route and date.

Book early, or pay a lot more at the gate. Both carriers charge well above their online rate if you wait to add a bag at the airport. Frontier's gate rate was a flat $99 regardless of route, over 40% above the online price on the routes tested. Allegiant's gate rate was a flat $75, also well above its online rate.

The takeaway: the price you see when you check is specific to that route and date, not a universal number for the airline. Add a bag during booking, not at the gate, and expect the number to move if your route changes.