How we read fares

1. Where the fares come from

Aviasales, a flight search engine, keeps the cheapest fares that its users found in recent searches and offers them through its Flight Data API. We read two kinds of figure from it for each departure city: the cheapest one-way fare to each of the destinations that travellers in the UK (or the US) search for most from that city, among those with a fare found, and, for the routes that have their own page, the cheapest one-way fare for each month of the next ten. Each figure comes with the departure day, the airline, the airports, the number of stops, the flight time and the search that found it. For the routes that have their own page we also read the cheapest fare for every departure day of those ten months, and a month's figure is the lowest of its days, so a route's page, its departure city's list and the guides all show one set of figures.

How fresh the figures are: the pages show the fares read in the daily run, in the morning, and keep them until the next run. This page asks the source now; a list elsewhere on the site may show the figure from this morning.

2. What a figure is not

• Not a live quote. A fare found in a recent search may have changed or sold out. The live search shows what is on sale now.
• Not a promise of availability on any day of the month. The month's figure is the cheapest fare found for a departure in that month.
• Not complete. A month without a figure is a month for which no fare was found, not a month without flights. Fares for dates far ahead rest on fewer searches than fares for next month.
• Not a forecast. There is no price history yet, so the site says nothing about when to book, only where the lower fares were found.

Fares are in the currency of the departure city: pounds for London, Manchester and Edinburgh, US dollars for New York, Los Angeles and Chicago. Every fare is one-way.

A fare marked "long connection" is a trip with stops that takes at least twice as long as the route's typical time: twice the typical direct flight time where the route has a direct fare, otherwise twice the shortest journey found. It is still the cheapest fare found for its month, and we show it, but the journey may not be the one you want. 43 of the 212 route-months on the route pages carry the mark today.

For connecting trips the airline shown is the one the search returned as the main carrier; other legs may be with other airlines.

3. How pages are built and sorted

Tables are sorted by fare, cheapest first, and never by commission. The cheapest month or day is the coral fold, and its fare sits on a white tab. A route gets its own page with fares found in at least six of the next ten months and keeps it while at least three months have a fare; 28 routes have a page today and 2 do not qualify yet, so they have no page. The opening paragraph of each page is written from that page's own figures, and the guides are computed from the same data across all routes.

4. How the link to the live search works

The fare slip under the folds names the day, the airline, the number of stops, the airports and the journey time, and its button opens Aviasales' search for that day. Until the affiliate account for this site is active, the buttons open the plain Aviasales search without any identifier; once it is active they become affiliate links, the line above each button says so, and your fare stays the same.

The site sets no cookies and loads nothing from a third party. When a link is affiliated, the button says so and opens the live search only when you click it; Aviasales or its network may then set their own cookies on their own domains. The privacy page has the details.

5. Reporting a wrong fare

If a figure on a page looks wrong, write to hello@farebulletin.com with the page and the figure. Corrections go into the next daily refresh. The terms of use describe how the site is paid for and what it promises.