People are more concerned about getting a good deal on a vacation than they are about any other discretionary purchase in their life, according to Google.

Average airfares trend upward 140–120 days ahead of departure, then drop about 90 days before, then hover for a while before starting to go up 20 days before, and then jumping up a week before

Advice? Buy early: The beginning of September is your best bet for getting a decent price, as fares are likely only to go up as we get closer to Thanksgiving and the December holidays.

Overall, independent of the destination, airfares are likely to go up 75 days before departure, and again 35 days before departure.

https://www.travelandleisure.com/travel-news/google-flights-hotels-great-value-rating