Finding the ancillary revenues mostly from bag fees is relatively easy. Compare financials before the fees were instituted versus after. The net increase is quite easy to calculate. As to the lost revenue, when have they ever said how much was attributed to having a bag fee in place?
Actually, doing it your way yields a meaningless result since "financials" vary from quarter to quarter and year to year anyway (publicly released, shorter intervals available to mgt). Depending on what you mean by "financials" (it's not a very specific term), US' "Other" operating revenue increased $21M YoY in the 3rd quarter - is that how much revenue the fees produced? Total revenue decreased nearly $540M - did the fees produce negative revenue? Operating profit/loss improved by nearly $700M - it that the fee revenue? You see the problem with your method.
Much easier, and accurate, is to simply add up the fees collected in each category - checked baggage being one such category. It stll doesn't represent the net gain in revenue, though. That will tell you (at least it'll tell management) how much revenue each specific fee brought in for that reporting period.
You might need to take an accounting class yourself. There is no such thing as bottom line in revenue.
Correct from a P&L statement perspective. But only looking at revenue, which we are, it's the total of all the revenue from various sources - ticket sales, cargo, mail, UM fees, ticket change fees, "talk to a person" fees, maint performed for other airlines, interest income, etc, etc. List them all, draw a line under the last one, add them up, and the number at the bottom - the "bottom line" - is the total. It's a number you won't find on a P&L.
When WN increases PAX revenue they have to actually give them a seat and all cost-driven services that go along with it. When you charge for a bag you would handle anyway, there is relatively little increase in costs so those revenues drop to the true bottom line.
Since WN is flying the seat around, there's very little extra cost per additional passenger, just as for the bag. That rational cits bpth ways. However, when US loses a potential pax because of the fees, they lose the revenue that ticket represents and any bag (or other) fee that pax would have paid.
The real point here is that if WN begins to charge for bags, where else would PAX go to avoid the fees? Nowhere among the majors so they would not experience the fabled book-away; so every dollar in the $300+ million dollar range would have an immediate impact on their bottom line and shareholder value.
Of course, they wouldn't gain market share due to the lack of fees either - how much is a 1% increase in market share gain worth? How about $800 million a year. Now, about that $300 million they're fools for passing up....
Jim