The price of the same seat on the same flight changes repeatedly before departure. The movement is produced by an inventory system, and understanding it explains behaviour that otherwise appears arbitrary.
Seats are sold from fare buckets
An aircraft cabin is divided not only into physical classes but into booking classes, each with its own price and conditions.
Only a set number of seats is made available in each bucket, and when a bucket is exhausted the system offers the next one up.
The fare therefore rises in steps rather than continuously, which is why a price can jump noticeably between two searches minutes apart.
Revenue management forecasts who is still to book
Airlines model expected demand for each flight based on historical patterns for that route, day and season.
Seats are withheld from cheaper buckets when the model expects enough later, less price-sensitive bookings to fill them at higher fares.
If those bookings do not appear, the system releases cheaper inventory again, which is why fares sometimes fall close to departure on routes with weak demand.
Business and leisure demand are separated by conditions
Cheaper fares carry restrictions such as advance purchase requirements, minimum stays and limited changes.
These conditions exist to prevent travellers who would pay more from buying the cheaper inventory, since the restrictions cost a business traveller more than they cost a holidaymaker.
The fare structure is therefore a sorting mechanism, and the conditions attached are as much a part of the pricing as the number itself.
Overbooking is priced in
Airlines sell more seats than the aircraft holds because a predictable share of passengers does not travel.
The overbooking level is set from historical no-show rates for that route and fare mix, since flights sold mainly on flexible fares see more late changes.
Compensation arrangements for denied boarding are defined by regulation and vary by jurisdiction, and those rules change over time.
What searching does and does not affect
Prices shift because inventory sells, seasonal models update and competitors adjust, all of which happen independently of any individual searcher.
Displayed fares also depend on the point of sale and currency, which is why the same itinerary can differ between country versions of a site.
The practical consequence is that a fare seen is a snapshot of bucket availability at that moment rather than a stable price for the seat.