How we work

For 295 routes from 15 German airports — and for each of them in the return direction too — Billigflugkalender shows when the flight was last cheapest: by month for the next twelve months and by day for the next three. Once you’ve found your day, the flight search shows the current offers. These are two different kinds of price, and we never mix them: the calendar shows prices found recently, the flight search shows offers available now.

Where the prices in the calendar come from

From the Travelpayouts Data API. It contains the prices that users of the Aviasales flight search found in their searches over the last few hours to days. We query it per route and month and receive, for each departure day, the lowest price found for a one-way flight, in euros, for the German market. We don’t mix in any other sources.

What “cheapest price found” means

A price for a one-way flight (outbound only) for one person in economy — without details of baggage or fare.
It is a price that was found in a search, not an offer and not a promise. It may be higher or lower when you book.
Days on which nobody searched have no price. Such days are shown with “–”; we don’t estimate anything.
A month’s value is the lowest daily price in it. Next to it, we show on how many days there were prices.

How up to date the prices are

We query the months of the daily calendar at most every six hours and the later ones at most every 24 hours — their prices change more slowly, and the source knows fewer days there. The pages themselves are rebuilt at most once an hour. Next to the figures, we show when they were retrieved. If a query isn’t possible at the moment, we show the last known data, but never data older than three days.

Why the price may differ when you book

Flight prices change constantly; a price found may already be gone once the cheapest seats are sold.
Baggage, seat selection and payment method can increase the price.
For two people or a return flight, the price is different from the sum of one-way flights for one person.

That’s why every day and every month in the calendar leads to our flight search, pre-filled with that day — that’s where the current offers are.

The flight search

For every search, our server queries two flight searches at that moment: Kiwi.com and Aviasales (via the partner network Travelpayouts). Both in turn query airlines and travel sites. We merge the answers into one list; the same flight appears once, with every provider and its price for all travellers. If neither returns anything, a fallback source steps in — which source answered and when is always shown above the list.
We answer an identical search from our cache for a few minutes (Aviasales five, Kiwi.com ten minutes) instead of asking the partners again.
Under “From”, you can choose up to five departure airports at once; the list then shows at least five flights from each airport with results. Only flights from the chosen airports are counted.
Above the list, you choose the order: “Best” (the default), “Cheapest” or “Fastest”. How it is determined is explained under “How we sort results” at the list. We don’t show offers from Booking.com (the operator’s decision) — nor their price.
Around your date, the search shows the cheapest prices of the neighbouring days that Kiwi.com currently gives, and in the calendar of the search form, guide prices per day from Kiwi.com — to help you choose the day, explicitly not offers.
“Everywhere” in the destination field shows all destinations by price in the chosen month: guide prices from other travellers’ searches on Aviasales, not live prices. Tap a destination to open the flight search for it.
We don’t pass your IP address or your browser identifier on to the flight searches. So that nobody can trigger searches en masse, there is a limit on new searches per connection; bots and search engines don’t trigger new searches.

Which airport is cheapest to fly from

On the destination pages (such as “Flights to Mallorca”), we compare the departure airports by the typical daily price: the median of the prices recently found per departure day over the next three months, from seven days with a price, and only if all three months could be retrieved. The median, because a single very cheap day says little about where you’ll fly cheaply on your own travel day; we still show the lowest single price next to it. There is only a ranking from two departure airports with enough data; departure airports with too few prices aren’t more expensive, just unknown.

Return trips

Every route page shows, for 3, 7 and 14 nights, the cheapest combinations of outbound and return flight — the sum of two one-way flights, each the lowest price recently found for one person. This is a guide price for two separate tickets, not a price for a return ticket: the source doesn’t know that in this form. The flight search then shows the current prices for exactly these days.

Airports

The source reads some airport codes as a whole city and then also gives flights from neighbouring airports — for Frankfurt, for example, from Frankfurt-Hahn, around 90 kilometres away as the crow flies. If the cheapest flight of a day departs from or lands at an airport that doesn’t belong to the route, that day doesn’t count; the page then says how many days that was. For cities with several airports (London, Paris, Rome, New York, Istanbul, Dubai, Bangkok), the same airports count as in our ranking of the most-flown destinations — Beauvais doesn’t count as Paris, for example, nor Frankfurt-Hahn as Frankfurt. Tapping a day searches from exactly the airport where that day’s cheapest flight departed and to the one where it landed.

How we calculate

Months: the first month is the current one if at least ten days are left, otherwise the next one. Only days from tomorrow onwards count.
Cheapest month: the month with the lowest daily price — only among months with at least three days with a price, only if there are at least four such months and all twelve months could be retrieved. Months without prices aren’t more expensive, just unknown.
Colour bands in the daily calendar: the daily prices of the three months are split into thirds — cheap, medium, expensive. Only from nine days.
Typical daily price: the median of the daily prices in the calendar, from seven days.
Weekdays: the median per weekday, only if each weekday occurs at least four times. If the cheapest and the most expensive weekday are less than 8 per cent apart, we write “hardly any difference”.
Month comparison (cheapest against most expensive month): under the same conditions.
Direct flights: how often the cheapest flight of a day had no change, from ten days.
A route only appears in search engines once there are at least ten days with a price in at least three months.

Which routes

The departure airports are Frankfurt, Munich, Berlin, Düsseldorf, Hamburg, Stuttgart, Cologne/Bonn, Hannover, Nuremberg, Leipzig/Halle, Dortmund, Bremen, Memmingen, Weeze and Frankfurt-Hahn. The 22 destinations come from our ranking of the most-flown destinations from Germany in 2025 — our own analysis of figures from the Federal Statistical Office of Germany (air traffic at main airports, passengers by destination airport). We chose holiday destinations whose price depends heavily on the time of travel, and the big cities. Long-haul destinations such as New York, Dubai and Bangkok are only listed from some of the seven large airports. From the smaller airports, there aren’t prices for every destination — such routes are shown with “no prices found yet” and don’t appear in search engines.

What we don’t know

Whether a price found is still available today.
Prices for an outbound and return flight as a package, for groups or in other classes — in the calendar. The flight search knows them.
How full a flight is or which airline will end up cheapest.

How we make money

The offers in the flight search are ads: if you book through one of them, we receive a commission. Your price stays the same. Only offers that our partners Kiwi.com and Aviasales find are compared — not all providers on the market. The commission has no influence on which month or day counts as cheap or on the order in which offers appear — that is decided by price, travel time and changes.