You can generally book flights up to about 11 months (around 330 to 337 days) in advance with most major airlines, especially in the U.S. This is the typical booking window for cash tickets on airlines like American Airlines, Delta, United, Alaska Airlines, and others. Low-cost carriers may have shorter and less standardized booking windows, often around 6 to 9 months ahead. However, booking flights this far in advance does not necessarily get the best price. For domestic flights, the best deals are often found when booking about 1 to 3 months in advance, while for international flights, the optimal booking time tends to be around 2 to 8 months in advance depending on the route and season. Award tickets using points can sometimes be booked as soon as the booking window opens, which varies by airline. Summary by airline booking windows for cash tickets:

• Alaska Airlines, American Airlines, Delta, United: ~$330-337 days in advance
• Southwest, Allegiant, Spirit, Frontier, Sun Country: typically 6 to 9 months in advance or variable

Booking far ahead secures flight availability but not necessarily the lowest prices, which often appear closer to the travel date within the windows noted above.