I'm not sure that these figures are accurate. They might work if you're looking at the rankings across all titles and genres; but the further you get down those genre listings, the less accurate they become. I know of people who have had their books at number one in several of Amazon's best-seller lists, but they've only sold a handful of books to get there.
Of course I mean ranking in store. I am 100% sure those ranking figures are accurate as of this month. You are right that being #1 in a subgenre list means nothing (though typically, the top 5 in Contemporary Romance and top 5 in F/SF, and top 5 in Thrillers, those broader and most popular categories, are also always top 100 in store and likely top 100 in national sales). I'm talking rankings of all books, including NF: "paid ranking in store." (I don't care about free in store. Meaningless to me, as it means no direct income for that product.) If you don't know how to find that on a book page, get on a computer and google "top 100 books Amazon" and then click on each individual book page and scroll down until you see the ranking list, typically four to six lines long, something like this:
Amazon Best Sellers Rank
#28 Paid in Store
#1 in Paranormal Romance (Books)
#2 in Paranormal Romance (ebooks)
#8 in Horror (Books)
(and so on)
That imaginary book is #28 in store, the 28th best selling book today at Amazon.com. I don't give a hoot about the rest of it (except when it's me at #1 in a genre, and then I only care for silly ego reasons.) It's right there for the world to see. Let's say that book is priced at 3.99 and is self-published. That author is selling about 2400 units today, times $2.70 royalty = $6500 gross income today on that book alone. You go to the author page, you look at every book under that name, its price, its ranking, and you can get the income on every book at Amazon. You go over to Barnes and Noble...do the same thing with a different formula, and go to Amazon.ca and Amazon.uk and so on. You add up all those figures, and you know at least 90% of what any author made today. You can compute what percentage was made at Amazon.com.
Let's say tomorrow the position #28 paid in store at Amazon.com is held by a person who has a trade-published paperback original instead--and to make it easy on me, the ebook is not out yet. The book is priced at 7.99. She's making a 6% royalty. Still selling 2400 units because of the store ranking, x $.48 royalty per book = $1150 income that day for that one book (of which her agent will get $170). If her book is out in paper, hardcover, and ebook, it's harder to estimate her gross income over the four biggest book sellers, but with the ranking formulas in hand, you can, if you feel moved to. I don't particularly recommend it, but I've done it.
You want to really spend some time with this exercise? Ranking for each book on each day is tracked over the past five years. You could look at every book of any author, for every day, and have a good estimate of any author's income (I often wonder if the IRS or other taxing agencies know about this.
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Anyone who has had rankings from top 20 down to 1,000,000 knows this formula from direct experience, as does anyone belonging to top-earning private writer groups, where people share their information and we can get down to X ranking in store = Y sales on any given day of the year, and we can and do share percentages of our income broken down by store/region/format so know what the ranges are.
While a few trade-published authors claim to be making lots of hidden money a stranger cannot determine by looking at sales rankings in all formats, all stores, all territories, if you ask them "where and how much exactly at each place?" they never answer with specifics, so color me skeptical. I've been in the biz too long, and know too many American and Canadian trade published midlisters to swallow vague references to hidden income amounting to much. Were it a true claim, the person claiming it would be able to produce the figures: royalty statements, a monthly bank account statement with business names blurred out, their 1040 or Schedule C, something. As none ever have, not even once that I'm aware of, I can't believe it. After thirty years in the business, with lots of friends in trade over the year, I know about all sorts of little side income, and none of it amounts to much expressed as a percentage. I remember how shocked I was as a younger person understanding how little something like a Japanese translation meant in income to the author. Sounds impressive, "I got a Japanese deal." But I never saw it come to five figures income among the people I knew. I saw a foreign deal come to only three figures several times! Hardly worth the time they spent reading the contract or talking on the phone about it.
Journalists at financial newspapers and magazines use the 70% figure for Amazon's percentage of the biz. In ebooks, they say, Amazon has 90%. It's not my figure; it's theirs, and I assume they know, for acquiring that sort of knowledge is their jobs, just as knowing the ranking/sales formula is part of mine as a publisher. For self-publishers, yes, Amazon might be higher than for the trade-published, and it can be 100% if we choose. Some self-publishing income is also hidden from you if you don't belong to the top-sellers' groups where people discuss it, including library sales, small bookshop sales, movie options, Prime Reading selection--and possibly the most impressive, KU bonuses, which can easily add ten thousand dollars to a self-published author's income every year. (None of us take NDAs serious. We know they are meant to screw us over, not to help us.) Some of us ghostwrite, same as in trade. And for those of us who have hybrid deals for audio or paper or whatever, you'd need to ask us what our tiered royalties look like in order to run the numbers for those formats, but again, we tell each other those figures.
And beyond X ranking in store = Y gross sales, it's true that author expenses vary. The trade published always have that 15% or higher bite from agents, and whatever else they choose to spend on. I spend little. Other self-publishers drop $200K on Facebook ads every year, or pay Amazon for enhanced book pages, have a VA, an accountant, a financial adviser, LLC expenses, a $3000 treadmill desk and a masseuse who comes in at the end of each writing day, and so on. So what I can't even guess at is how much any writer is putting in the bank except for me and my closest friends in the biz, who net from "hardly anything" for a newer writer working the ads pretty hard up to "more than I know how to spend." But anyone can see with a high degree of accuracy the maximum any author might be grossing in paperbacks, audio, and books. Certainly, I understand several reasons why some people would be upset that anyone with the formulas can now do so--perhaps they're selling advice to wannabe writers and if everyone knew how unsuccessful they actually are as novelists, that other/probably larger part of their income would fall off, or perhaps they were taught it's impolite to discuss money, or perhaps publishers or agents convinced them it's not to their benefit to understand what's going on in the business or how the money end works (when it most definitely is to the writer's benefit), or perhaps they are ashamed of their low income, even though that's the situation of most writers most years, or perhaps, as some have suggested, someone is paying them to lie, though that seems a bit too conspiracy-theory for me! Knowing as many writers as I have over the years, I knew a couple who were self-aggrandizing or compulsive liars...but the days when such people can lie about book-writing income are gone. The truth is out there, naked, standing in the town square. Anyone with the basic knowledge can see it.