The short answer: Seven weeks before takeoff. On average, fares bottomed out 49 days before the flight, then increased slightly, but remained steady until about a month out. After that, prices climbed as the travel date approached. But too much advance planning isn't good for the bottom line, either. Though, not surprisingly, the highest fares, came with bookings made 11 or fewer days in advance, the next worst timing was 208, 209, and 210 days out, according to the analysis.