The number that surprises people
Royalty on a paperback is not a percentage of the cover price. It is a percentage of the cover price with the printing cost taken off, and the printing cost is driven almost entirely by page count. A 400 page book costs roughly twice as much to print as a 200 page one, so two books at the same price can pay very differently.
This is where a first paperback goes wrong. Someone prices a long book at what feels reasonable next to comparable titles, and the margin left after printing is a few cents. The fix is to run the number before the price is set rather than after the first royalty statement.
How the two rates work
A paperback earns the higher royalty rate at and above a threshold list price, and a lower rate below it. That produces a cliff rather than a slope: pricing a book just under the threshold can pay less per copy than pricing it just over, even though the buyer pays less. The calculator shows which side of that line you are on.
Kindle works differently. There are two plans, and the higher one is only available inside a price band. Above or below that band you drop to the lower rate, which is less than half as much per sale. The higher plan also carries a delivery charge based on the size of the file, which is why an image-heavy book can earn noticeably less than a plain text one at the same price.
The minimum list price, and why it exists
Every paperback has a price below which it cannot be listed. The retailer takes its share off the top, and what is left has to cover printing. If the list price is low enough that it does not, there is no price to publish at, and the upload is rejected.
Working backwards from that floor is the useful move. It tells you what the book has to be worth to a reader before it is worth printing at all, and on a long book the answer is often higher than the author expected. If the floor comes out above what the market will pay, the lever is page count rather than price: tighter interior design, a smaller trim size, or fewer pages.
Where these numbers come from, and when to check them
The rates here are Amazon's published figures for the Amazon.com marketplace on standard distribution, and the date they were last checked is printed under the results. Amazon changes them, expanded distribution pays differently, and other marketplaces have their own printing costs in their own currencies. Treat this as the arithmetic done correctly against a known table, and confirm the table against KDP before you commit to a price.
One thing the calculator cannot tell you is whether the book is worth its price, which is mostly a question of how it looks. A well-designed interior and a cover that reads at thumbnail size support a higher price than a converted manuscript does. Designrr builds that side of it, turning your content into a laid-out book with templates, a cover designer and an automatic contents page.