Airline seat pricing is a real-time optimisation problem rather than a price list.
Revenue management
Seats allocated to fare classes and released as demand develops.
Which is why prices move in steps rather than smoothly.
Demand forecasting
Historical patterns predicting how a flight will fill.
The myths
Cookies raising prices and a best day to book.
Which investigations have generally not supported.
Why prices rise near departure
Cheaper fare classes selling out rather than a deliberate increase.
What actually determines the price you see
How many seats remain in each fare bucket, how the flight is filling relative to forecast, and how much competitors are charging on the same route.
Which are all properties of the flight rather than of you.
The persistent belief that searching repeatedly raises prices has been tested by consumer organisations and journalists repeatedly, and has not been substantiated.
Fare classes
The same cabin sold at many different prices with different conditions.
Which is why two neighbouring passengers paid very different amounts.
Ancillary revenue
Bags, seats and extras as a growing share of income.
Which makes headline fares less comparable.
Route economics
Competition determining pricing freedom.
Practical advice
Flexibility on dates matters more than timing the booking.
Why the same seat costs different amounts
Airlines sell a limited number of seats in each fare bucket, and once a bucket is exhausted the next available price applies.
Which produces the step changes travellers notice.
The system is designed to capture both leisure travellers booking early on price and business travellers booking late on convenience, from the same aircraft.
Overbooking
Selling more seats than exist based on expected no-shows.
Which is legal and compensated when it goes wrong.
Codeshares and alliances
The same flight sold by several airlines.
Which affects pricing and passenger rights.
Passenger rights
Compensation regimes for delays and cancellations.
Which differ substantially by jurisdiction.
Practical points
Compare total cost including baggage rather than headline fare.
What actually reduces what you pay
Flexibility on dates and airports, travelling outside peak periods, and comparing total cost including bags and seat selection.
Which are unglamorous and are what the evidence supports.
The various tricks that circulate, incognito browsing, booking on particular weekdays, clearing cookies, have been tested repeatedly and do not hold up.
Fare comparison sites
Useful for finding routes and not always showing full cost.
Which makes checking the airline directly worthwhile.
Cancellation and change fees
Cheaper fares carrying stricter conditions.
Which is the actual trade being made.
Loyalty programmes
Value varying enormously by programme and by redemption.
Consumer protections
Rights on delay and cancellation set by jurisdiction.
Why it is worth knowing how these things work
Most of the systems that shape ordinary life are invisible by design. Nobody explains why a parcel took an odd route, why a film left a streaming service, why a wait in an emergency department extended, or why the price of a flight changed between two searches.
The absence of explanation is rarely deliberate concealment. It is that the people running these systems are solving their own problems, and the reasoning behind their decisions is obvious to them and completely opaque from outside.
Understanding the mechanism does not always change what you can do about it. It does remove a category of low-grade frustration that comes from assuming something is arbitrary, unfair or aimed at you personally when it is usually none of those things.
A note on sources
Where regulation is involved, national regulators publish the actual rules and they are generally clearer than press coverage of them. Where an industry is involved, trade publications aimed at people working in it are considerably more informative than consumer coverage.
Practices described here vary substantially between countries, and anything with legal, financial or medical consequences warrants checking against the rules that apply where you are.
The pattern that recurs
Across almost all of these systems, the same three things turn out to be true. The behaviour that looks irrational from outside is optimising for something the observer cannot see. The cost that seems unexplained is usually concentrated in one specific stage of the process. And the information that would resolve the confusion is generally published somewhere and read by nobody.
That last point is the most useful one. Regulators, operators and industry bodies publish an enormous amount of explanatory material that answers exactly the questions people complain about not being able to get answers to. It is dry, it is not promoted, and it is free.
What to do with any of this
Very little of it changes a decision on its own. What it changes is the ability to ask a better question: of a company, of a service, of a regulator, or of yourself before assuming that something went wrong.
A final caveat
Everything above describes general practice. Individual companies, jurisdictions and circumstances differ, sometimes substantially, and the rules change more often than summaries of them get updated.
Where a decision matters, the official source for your own country is worth the ten minutes it takes to check.