For Southwest Airlines flights, it is recommended to check in exactly 24 hours before your scheduled departure to secure the best boarding position. Southwest uses an open seating policy where boarding groups (A, B, or C) and position numbers are assigned based on check-in time. Checking in right at the 24-hour mark gives you the highest chance of boarding early and selecting your preferred seat. If you cannot check in manually, Southwest offers an EarlyBird Check-In option for a fee, which automatically checks you in 36 hours before your flight and usually grants an earlier boarding position, though it does not guarantee a specific seat. Families traveling with children under six have the benefit of Family Boarding, which allows one adult traveling with a child to board between Groups A and B, regardless of check-in time.

If you miss the 24-hour check-in window, you can still check in up to 60 minutes before departure for domestic flights and 75 minutes before for international flights. However, checking in late will likely result in a later boarding group and fewer seat choices. Airport check-in counters and kiosks generally close 45 minutes before departure, so arriving early enough to drop bags and get to the gate is essential. In summary, to ensure the best boarding position and seat selection, Southwest passengers should check in as close to 24 hours prior as possible. EarlyBird Check-In can provide automatic early check-in, and Family Boarding helps families with young children. Even if you check in later, you can still board, but your options may be limited.