Most writing about ancillary revenue is either an airline trade piece that assumes you are an airline, or a vendor page that assumes you have already decided to buy something. These are neither.
In short
This section explains how ancillary revenue works, why the window after booking converts differently from the booking flow, and how to measure any of it honestly. It is written for commercial and distribution leads at travel sellers, and it contains no benchmark figures we cannot source.
Start here
Two pillar pieces carry the argument. Ancillary revenue covers the category from first principles: how unbundling created it, which categories behave differently and why, and where the revenue leaks when the seller is an intermediary rather than the airline. Post-booking upsell picks up where that leaves off, and explains why the same traveller who refused a seat fee during checkout will pay for one a week later.
Then the mechanics
The cluster pieces each take one thing and go deep. Attach rate is the one most worth reading before you quote a number to anyone, because the denominator you pick changes the answer more than the performance does. NDC versus ATPCO is the most technical, and the one to send to a colleague who keeps asking why the range of sellable extras differs by booking. Seat and baggage revenue cover the two categories that carry most of the volume.
On the missing numbers
You will notice there are no industry benchmarks anywhere in this section. That is deliberate. We do not have figures we can attribute, and a plausible number with no source attached is worse than no number, because it gets quoted onward. The benchmarks piece explains where real published data lives, how to read it critically, and how to build an internal baseline that is worth tracking.
Where arithmetic appears it is explicitly illustrative, using round numbers you can replace with your own.
Frequently asked questions
Who are these written for?
Commercial and distribution leads at online travel agencies, travel agencies, and airlines. They assume you know the industry and do not assume you have worked on ancillaries specifically.
Why are there no benchmark numbers?
Because we have none we can honestly publish. Rather than repeat an unsourceable industry figure, the benchmarks page explains how to read published data critically and how to build a baseline you can actually trust.
Where should I start?
Ancillary revenue if you want the category from first principles, post-booking upsell if you already know the category and want to understand why the window after booking behaves differently.