Research from flight Promotional Codes comparison website Skyscanner.net this week claimed that the best time to book a flight for the cheapest fare was, on average, five weeks ahead of the departure date. The website came to this conclusion by analysing over 200 million searches and the actual prices paid by customers over three years.
The best time to book for Britain's leading summer destinations ranged from three weeks before travel for those heading to Greece and 21 weeks ahead for those going to the USA. Skyscanner found that those who booked at the optimum time for the USA saved £120 compared to booking during the week of departure.
The general rule is that: the more seats there are available, the cheaper tickets will be, according to Sophie Butler, our advice columnist. Therefore it pays to book early. However, if many seats remain available near to the departure date, which can happen for flights in non-peak, non-holiday periods, the airline may hold a seat sale, meaning that last-minute bargains can be snapped up.
It is worth considering though, that if you're travelling as a group or family and leave booking flights to just five weeks before departure, there may not be enough seats left.
Nick Trend, Telegraph Travel's consumer editor, said: "The best advice for when to book flights depends both on when you want to travel, and how flexible you are able to be.
"If you are a family who wants to fly during the school summer holidays on a particular date, you should certainly book now. If you leave it later there is a very high risk you will pay a much higher fare, and may not even be able to book the flights you want at all."
Final destination is important too. If you can be flexible about where you want to travel, you may be able to pick up a very good value fare close to the departure date. But if you have your mind set on a fixed destination, particularly in peak holiday periods (which may differ according to the location - December for the Caribbean, and July for Spain or Italy, for example) then you would be wise to book as soon as possible.
A spokesperson for Skyscanner said: "There may be other times throughout the year when customers might get a cheap flight and of course many people will be more comfortable booking further in advance, especially as prices close to departure can be quite volatile."
She added that if customers wanted to get the best deal, they would be best researching prices and tracking fares by signing up for price alerts, which allow travellers to see when low fares become available.
It also pays to compare fares using several price comparison websites before booking, as Donald Strachan, Telegraph Travel's technology expert, advises here.
In addition, the Skyscanner research looked at the average per person return price for Britons' top ten August destinations. They found that the average fare for Spain, for example, was £153. But again, there are so many variables even within travel to one country that it is difficult to give overall averages. For example, in Spain, flight prices to Madrid generally plummet in August due to the heat, but increase to coastal destinations such as Malaga.
Overall, there is no one fixed answer to when it is best to book a flight. The answer depends on multiple factors, including whether you are flying short or long haul, during peak or off-peak periods, and whether you are set on a specific destination.