How airline pricing works, and why flight prices keep changing

An airline does not set a single price for economy on a flight. It divides the seats into groups, often called fare classes or fare buckets, each with its own price and its own rules. The cheapest group might allow no changes and no checked bag, while a more expensive one in the same cabin can be changed or refunded.

Each group has a limited number of seats on sale. When the cheapest group sells out, the next one becomes the lowest price available, so the fare steps up even though nothing about the flight has changed. This is the main reason prices jump rather than drift.

Airlines forecast how full each flight will be, using how past flights on that route sold and how bookings are going this time. If a flight is filling faster than expected, fewer seats are offered at the lower prices. If it is selling slowly, cheaper seats can be opened up again, which is why fares sometimes fall as well as rise.

Demand follows patterns you can predict. School holidays, public holidays, big events and popular days of the week all push fares up. Early morning, late night and midweek flights are often less popular, and therefore often cheaper. Our cheap flight tips list practical ways to use this.

The same distance can cost very different amounts on different routes. Where several airlines compete, especially if a low-cost airline is one of them, fares tend to be lower. Where one airline has the route to itself, it has less reason to discount.

This is also why a journey with a connection is sometimes cheaper than the direct flight, even though it uses two planes. The airline with the connection is competing for your booking against the direct flight, and price is how it wins. Comparing nearby airports works for the same reason, as our guide on how to find cheap flights explains.

As a general pattern, the cheapest groups of seats sell first, and people who book close to departure are more often travelling for work or in an emergency and will pay more. So fares usually climb in the final weeks before a flight.

Booking very early is not always cheapest either, because airlines may not release their lowest prices until they can see how a flight is selling. There is no single best day or number of weeks that holds for every route, and any figure you read is an average at best. A more reliable habit is to start watching prices early, set a price alert, and book when the fare is good for your dates rather than waiting for a perfect one.

The amount you pay is the airline's fare plus taxes, airport charges and any surcharges the airline adds. The taxes and airport charges depend on the airports and countries involved, so two fares that look similar can be built very differently.

Rules in several places are designed to stop the headline price from misleading you. In the European Union, the price shown must include all unavoidable taxes, charges and fees from the start, and optional extras have to be something you choose to add. In the United States, advertised fares must likewise include taxes and mandatory fees. Extras such as bags and seats still sit on top, and our guide to budget airline fees explains how to add them up.

A fare that changes between two searches, or between the results page and the payment page, usually has an ordinary explanation.

Many people believe that airlines raise the price because you searched before. There is little evidence for this, and the reasons below explain most cases. If you want to rule it out, compare in a private browser window, which costs nothing.

Because price follows demand and fare rules, the most useful things you can change are your dates, your airports and the fare type you choose. Check a few days either side of your preferred dates, compare the total with the bags you need, and read the change and refund rules before you pay for the cheapest option.

When you have a fare in mind, put it into our free trip budget calculator with accommodation and daily spending to see the whole trip, or let the AI trip planner draft a plan with flight options and a budget estimate for your dates.