To work out monthly average costs, KAYAK takes all selling prices for monthly over the last 12 months for spherical-journey flights from London to Atlanta, gets rid of the very best 0.one% to account for outliers, and after that usually takes the median of all values for monthly. I tried https://www.diigo.com/item/note/b7ses/hp8q?k=40d4190b930dd32c6890a175cc8e700e