The charts “When is the cheapest time to fly?”, “How far in advance should I book?”, “What's the cheapest day of the week to fly?” and “What do round-trip flights from New York City to Paris cost?” are built from the prices Priceline customers actually paid for flights on this route over the past 12 months or more.
Where a route has too few bookings to fill every point in a chart, we borrow the shape of the curve from a group of routes with similar price behavior and fit it to the fares booked on this route.
Because past fares don’t reflect today’s market, we then adjust the historical prices for current conditions such as inflation and fuel costs, using the round-trip fares found in recent searches on this route.
The chart “When is the best time of day to fly?” is calculated directly from the fares found in recent searches, not from historical bookings.