To calculate day-to-day ordinary costs, KAYAK normally takes all charges for day after day just before departure over the past year for flights from London Heathrow Airport to Austin, removes the top 0.1% to account for outliers, and then can take the standard of many of the values for monthly. https://businessclassflightstosydneyfromuk.home.blog/2024/07/23/some-insights-about-popular-holiday-packages/