Why do last minute flights cost more?

Have a question? Ask our expert Simon Calder

Travel hack: going via Lisbon could save money on a Spain to UK flight (Simon Calder)

Q Recently, I wanted to go to Madrid for the day, departing from any London airport on any day from Monday to Friday. Although I found relatively cheap flights with easyJet, British Airways and Iberia in the morning, the flights that left Madrid in the evening were expensive. Also, I noticed that flights gradually increase in price the nearer the departure date and time is. Is there any reason for this? I would have thought that if airlines can’t sell seats, they would reduce the price in order to attract customers. But this does not seem to be the case.

Name withheld

A First, let me tackle the question of whether fares should rise or fall as departure approaches.