You can generally book a flight as far as about 11 months (or roughly 330 days) in advance with most major airlines in the U.S. For example, American Airlines, Delta, Alaska Airlines, Hawaiian Airlines, and United Airlines typically open their booking windows around 330-331 days before departure

. However, low-cost carriers often have shorter booking windows, usually ranging from 6 to 9 months before departure, and some vary even more

. Regarding the best time to book for the best price:

• For domestic flights, the optimal booking window is usually 1 to 3 months before departure

• For international flights, it is generally best to book 2 to 8 months in advance, with some recommendations suggesting starting to monitor fares 6-7 months ahead and booking 3-5 months before travel

Booking too far in advance does not necessarily guarantee the lowest prices, and last-minute deals are rare. Airlines use dynamic pricing algorithms, so prices fluctuate frequently

. In summary:

• Earliest booking: about 11 months in advance for most major airlines.
• Low-cost carriers: typically 6 to 9 months in advance.
• Best booking window for domestic flights: 1–3 months before travel.
• Best booking window for international flights: 2–8 months before travel.
• Prices often increase significantly within the last three weeks before departure

This means you can book very early if you want to secure a seat, but for the best deals, timing your booking closer to these optimal windows is advisable.