A recent study by Expedia and Airlines Reporting Corp (ARC) based on thousands of flights in 2016 found the best prices on weekends and especially Sunday. Numbers were crunched by Expedia and were gathered by ARC, online and brick and mortar agencies. Flights within the US were 11% cheaper. Flights from the US to Europe were 16% cheaper and from the US to Asia 10% cheaper. As usual good luck on finding the best fare.