What is a fare basis code?
A fare basis code is the alphanumeric code that identifies a specific airline fare and links it to the rules — booking class, restrictions, refundability and validity — that apply to it.
Fare basis codes typically start with the booking class letter (for example Y, M or Q) followed by characters that the airline uses to signal season, day of week, advance purchase, minimum stay or passenger type. The exact meaning of later characters is airline-specific; the authoritative source is the fare rules attached to the code.
Why engineers care
Two fares can share a booking class but have different fare basis codes and very different rules. Pricing engines, refund calculators and exchange logic must therefore key on the fare basis and its rules, not on the cabin or booking class alone.
In NDC channels the airline may express the same information as a fare family and offer conditions rather than a filed fare basis, which is another reason to normalise fare data internally.