To calculate regular monthly regular price ranges, KAYAK takes all prices for monthly during the last year for round-journey flights from London to Atlanta, gets rid of the highest 0.1% to account for outliers, then can take the median of all values for every month. These are generally the Airways https://www.reddit.com/r/BusinessClassFlight/comments/1gat1os/what_are_the_top_tropical_destinations_to_heat_up/