Ask Dr Travel: When to book for best prices

When is the optimum time to look for best prices prior to a departure date which is pretty fixed, and can only be flexible by a few days either way for work reasons? Anne Wood, Elgin

The short answer is mercifully concise: if demand for flights when you want to travel is high, then book as soon as you are able to commit. Fares at busy times almost always increase relentlessly from when they first go on sale (usually just under a year ahead) to the day of departure. But if you are travelling off peak, then you can be much more relaxed, and plan to buy the trip some time between two months and two weeks before departure.

Let's assume you are able to fly off peak. This has three advantages: you need not hand over a wodge of cash way in advance; you are insulated against the financial loss if an unforeseen event wrecks your travel plans; and there's a good chance that the fare will fall. Airlines keep careful track of the sales patterns of individual departures, and any flight that is selling "below trend" is likely to have the fare nudged down in a bid to lure passengers on board.

The thorny question is: how can you tell if demand is high? The big clue is: school holidays (with England's school timetable having a much stronger effect than that of other parts of the UK). Christmas, New Year, Easter, late July and all of August are guaranteed high season. Half terms, too, increase fares at least for destinations within around five hours' flying time. But even if you can avoid English school breaks, beware of other countries' holidays: the US habit of taking a "spring break" in February or March distorts accommodation prices in destinations such as Florida, Mexico and the Caribbean. And any big conference or sporting event will play havoc with "normal" fares.

So, back to an even shorter answer: travel conventionally, and you need to book ahead; plan to fly counter-intuitively, and you should find a bargain.