You can check in for your Southwest Airlines flight exactly 24 hours before your scheduled departure time. Because Southwest does not assign seats and instead uses a boarding group system (A, B, or C), checking in the very second that 24-hour window opens is crucial for securing a better position. If you want to skip the manual scramble, you can purchase "EarlyBird Check-In," which automatically checks you in 36 hours early. For those who wait until they get to the airport, you can still check in at a kiosk or counter up to 30 minutes before a domestic flight or 60 minutes before an international one. However, being that late usually results in a "C" group boarding pass, meaning you'll likely be stuck in a middle seat toward the back of the plane.