When to book airfare
Buy at the right time - The sweet spot is 6–12 weeks out
Never buy your plane tickets more than about 3 months before your departure date.
Why? Because no one is discounting those seats yet, so you'll pay top dollar—which is misleadingly called the "lowest published fare."
But don't wait too long to buy, either.
A few years ago, the troubled airlines were throwing near-daily last-minute fire sales of unsold seats in a desperate attempt to avoid flying half-empty planes. Those days are gone.
What's the sweet spot, then? I’d say (a) check out the undiscounted rack rate for your intended flight about three months out, (b) then idly keep track of the fares and keep an eye out for sudden sales, and (c) if no sale comes along by about six to ten weeks out from your travel date, then you go ahead and buy.
That's when airfare consolidators lock in their fares, and most airlines will already be running sales by then if they plan to.
Keep in mind that, as a general rule, the cheapest tickets will sell out more quickly during peak travel season. Last-minute sales will pop up closer to travel dates in low season. In other words, wait a bit longer to buy in winter than you would in summer.