While most airlines allow you to check a bag up to 50 pounds, Spirit and Frontier cap the weight of a standard checked bag at 40 pounds. After that, you'll pay a pretty penny for overweight bags.

Spirit passengers will check in at Terminal 2 and use gates G4, G6, G8 and G10 in Terminal 3, a short walk away. Meanwhile, American Airlines will grab Spirit’s old gates in Terminal 3.

American Airlines will utilize Spirit's previous gates in Terminal 3's L Concourse. The CDA said signs will be posted at Terminal 3 check-in to direct passengers to the correct location.