Dear Geist,
How do publishers calculate advances when they accept a book for publication? I'm asking everyone what advance they got. Not everyone tells me, but lots do, and there's no pattern to the numbers. The advance seems completely unrelated to the length of the book or the track record of the writer or anything else. Am I missing something?

Dear R,
First, a note on author income for all readers of this post. The author earns royalties, a percentage of the sales of the finished book. Months or years may pass between the signing of the contract and the distribution of the finished book, so the publisher and author (or author's agent) often negotiate an “advance” for the author on those future royalty payments. The amount varies according to various criteria: the publisher's estimate of audience size; competition with similar titles in the marketplace; the author's existing audience thanks to earlier books, social media presence, high-profile activities in other fields; etc. Or an advance can be driven higher for other reasons, such as an auction among two or three publishers who all want to publish the book.
The convention in trade publishing is
to make an author pay back an advance if it exceeds the royalties earned. To make things even more interesting, every book is a different marketing challenge—even a book by the same author in a similar genre. So publishers go to some trouble to get the numbers right.
—The Editors