Last reviewed by Robert Prime, 28 October 2026. Sources read that day: Amazon KDP’s Make Your Book More Discoverable with Keywords, KDP Categories and Sales Ranking.
Quick Answer: Amazon ranks books on two things: what the book is and how it sells. Your keywords, categories, title and description tell Amazon what the book is, so it knows which searches and shelves to show it on. Then, in Amazon’s own words, keywords work “along with factors like sales history and Amazon Best Sellers Rank” to decide how high it appears. Best Sellers Rank is “based on customer activity of your book relative to the activity of other books”, and recent activity counts most. Amazon does not publish the full formula, so anyone who claims to know it exactly is guessing.
Table of Contents
- The two kinds of ranking on Amazon
- What Amazon says decides search placement
- How Best Sellers Rank works
- What you control, in order of impact
- What Amazon does not say
- Why a book stops ranking
- Check your own book
- Frequently asked questions
The two kinds of ranking on Amazon
When authors say “ranking” they mean one of two different things:
- Search placement. Where your book appears when a reader types “cosy crime set in Cornwall” into Amazon. This is the one that brings new readers.
- Best Sellers Rank (BSR). The number under Product details on your book page, plus your rank in up to three category lists. This is a scoreboard of recent sales and borrows compared with other books.
They feed each other. Amazon’s keyword page names Best Sellers Rank as one of the things that affect search placement, and a better search position brings the sales that lift Best Sellers Rank.
What Amazon says decides search placement
Amazon’s KDP help page on keywords says:
“Along with factors like sales history and Amazon Best Sellers Rank, relevant keywords can boost your placement in search results on the Amazon Store.” — Amazon KDP: Make Your Book More Discoverable with Keywords
That one sentence gives you the three parts:
- Relevance: do the words a reader types match what you told Amazon about the book? That comes from your keywords, title, subtitle, categories and description.
- Sales history: has the book sold over time?
- Best Sellers Rank: is it selling now, compared with other books?
Relevance gets you into the results at all. Sales decide how high you sit once you are there. A book with perfect keywords and no sales sits low; a book that sells well but is described badly never appears for the searches that would suit it.
Keywords
KDP gives you up to seven keywords or short phrases per book. Amazon’s own advice on that page is worth following closely:
- Think like a reader: “Imagine how you’d search if you were a customer.”
- Do not repeat words already in your title, contributor names or categories.
- No claims about quality (“best novel ever”), nothing time-limited (“new”, “on sale”), and no other authors’ names: Amazon says it has “a zero tolerance policy for metadata that is meant to advertise, promote, or mislead”.
- Single words often work better than quoted phrases. Amazon’s example: if you enter “complex suspenseful whodunit” in quotation marks, “only people who type all of those words will find your book”.
- “You can change keywords and descriptions as often as you like.”
Our step-by-step guides: how to fill all seven KDP keyword boxes and KDP keyword research.
Categories
You choose three categories in KDP. Amazon calls them “digital shelves” and says your categories, “along with keywords you select, tell Amazon where to ‘shelve’ your book”. Its advice is to “balance popularity and relevance”: popular enough that readers browse there, not so broad that the book gets lost.
Two warnings from the same page (KDP Categories):
- New categories “can take up to 72 hours to display”.
- If you pick a category that does not match the book, “KDP may remove or change the category”. Amazon says it does not tolerate “categorization that misleads readers”.
Our guide: choosing the right Amazon categories.
Title, subtitle and description
These are what Amazon and the reader both read. Amazon’s keyword page notes that “customers are more likely to skim past long titles (over 60 characters)” and that you should “focus your book’s description on the book’s content”. Guides: writing a book description that sells and book title strategy.
How Best Sellers Rank works
Amazon explains Best Sellers Rank on its Sales Ranking help page. In plain English:
- Amazon: Ranks are “based on customer activity of your book relative to the activity of other books”.
What it means: Your rank is a comparison. It can move when your sales stay the same. - Amazon: “Rankings are updated at least once per day, but changes may take up to 2 days to appear”.
What it means: Don’t judge a promotion by the next hour. Give it two days. - Amazon: “Rankings reflect recent and historical activity, with recent activity weighted more heavily”.
What it means: A burst of sales this week counts for more than the same sales last year. - Amazon: “Books can be ranked in up to three Best Seller Category lists”.
What it means: You appear in at most three category charts, and your customer activity decides which three. - Amazon: “Each available format of your book… has its own independent Amazon Best Sellers Rank”.
What it means: Your ebook and paperback rank separately in the overall charts. - Amazon: Canceled orders “are not counted”.
What it means: Only real demand counts. - Amazon: “One sale of a very popular book may not influence its rank much at all, but one sale of a lower volume book may significantly improve that book’s rank”.
What it means: A handful of sales can move a quiet book a long way, and it can fall just as fast.
Free promotions are counted on a separate list. In the Kindle Store, a KDP Select book on a free promotion ranks in the Free list, and “once the free promotion is over, your book’s previous Paid rank will influence its new rank” in the Paid list. Free downloads do not count towards the Paid charts. See our free promotion strategy guide.
Amazon also warns that buying or borrowing activity from “accounts that are attempting to manipulate our services” may result in “termination of your account and loss of royalties”. Paid “ranking services” and review swaps are a risk to the whole account, not a shortcut.
What you control, in order of impact
Amazon does not give weights, so this order is our judgement from working on authors’ books, not an Amazon ranking:
- The right shelf. Three accurate categories and seven reader-language keywords. This decides which searches you can appear in at all. It is free and you can change it any time.
- A page that turns visitors into buyers. Cover, title, the first lines of the description, price, the Look Inside sample, A+ Content and reviews. Amazon does not list these as ranking factors, but every sale they win feeds “sales history” and Best Sellers Rank, which Amazon does name.
- Sales momentum. Because recent activity is weighted more heavily, a launch, a price promotion, an email to your list or Amazon Ads all help most when they land close together. Our launch strategy guide covers the timing.
- Series and format links. Linking your ebook, paperback and series pages means a reader who finds one finds the rest. Use Author Central for your author page.
What Amazon does not say
You will read a lot online about “the A9 algorithm” or “A10”. Those are names other people use. Amazon’s KDP help pages do not describe a named algorithm or publish its weights. What Amazon does say is in the quotes above. Be careful with any advice that claims to know more, especially if it comes with something to sell.
Amazon’s shopping assistant, Rufus, now answers some readers’ questions on Amazon too. That is a different way of being found. See Amazon Rufus and books.
Why a book stops ranking
If a book that used to sell has dropped out of sight, the usual causes, in the order we check them:
- Sales stopped. Recent activity counts most, so a book with no recent sales sinks, even with perfect keywords.
- Wrong shelf. Categories that do not match the book, or keywords that repeat the title and waste the boxes.
- The page doesn’t convert. Readers arrive and leave. Look at the cover at thumbnail size, the first two lines of the description and the price against the top books in your category.
- Other books got busier. Rank is relative. Your rank can fall when your sales stay the same.
More on this in why is my KDP book not selling?
Check your own book
Amazon is now one of three places readers find books. The others are AI assistants such as ChatGPT, Claude and Gemini, and the open web. Our book discoverability guide explains all three.
Book Score checks your book on all three. Paste your Amazon link and the free check gives you a score out of 100 and the three fixes worth most, in about a minute. The full report (£49, including VAT) adds 72 real AI answers about books like yours, the books AI names instead of yours, and every fix written out.
Check my book free with Book Score →
Frequently asked questions
How does Amazon rank books?
In search, Amazon uses how relevant your book is to the words the reader typed (your keywords, title, categories and description) “along with factors like sales history and Amazon Best Sellers Rank”, in the words of its KDP help. In the Best Seller lists, it ranks books by customer activity compared with other books, with recent activity weighted more heavily.
How often does Amazon update Best Sellers Rank?
Amazon says rankings “are updated at least once per day, but changes may take up to 2 days to appear”.
Do Kindle Unlimited borrows count towards ranking?
Amazon’s Sales Ranking page talks about “customer activity” rather than just sales, and refers to “purchasing or borrowing activity”. It does not break down how borrows are weighted. See our Kindle Unlimited guide.
Do reviews affect Amazon ranking?
Amazon’s KDP help pages do not list reviews as a ranking factor. Reviews help a reader decide to buy, and sales are what Amazon says it ranks on. Never pay for reviews or swap them: Amazon can close accounts for manipulation.
How many keywords and categories does KDP allow?
Up to seven keywords or short phrases, and three categories per book. Both can be changed after publishing; new categories can take up to 72 hours to show.
What is the Amazon A9 algorithm?
“A9” and “A10” are names used outside Amazon for its search system. Amazon’s KDP help does not publish a named algorithm or its weights. It says keywords, sales history and Best Sellers Rank affect search placement.
