Here’s a publishing stat that should bother you more than it does: according to WordsRated, 90% of self-published books sell fewer than 100 copies.
When authors hear that, they usually diagnose the obvious suspects. The writing. The cover. The crowded market. And sometimes those are the problem.
But a massive share of those books fail for a quieter reason: nobody ever saw them. Not because the book was bad, but because the keywords attached to it didn’t match anything real buyers type into Amazon’s search bar. The book was invisible from the moment it was published.
The good news is that keyword research is completely learnable, and you can do a solid job of it without buying any software. This post walks through the free method, step by step.
How Amazon Decides Which Books Get Seen
It helps to get one mental model right: Amazon is a search engine. People type phrases, and Amazon returns products it believes match those phrases and are likely to sell.
For your book, Amazon reads three main signals: your title, your subtitle, and the seven backend keyword slots you fill in when you publish through KDP (each slot holds up to 50 characters). Together, those tell Amazon’s search engine what your book is about and which searches it should appear in.
If those signals match the phrases buyers actually search for, your book can surface, get clicks, get sales, and rank higher, which increases its visibility. If they don’t, the book’s quality never even gets a chance to matter.
The Keyword Mistakes That Make Books Invisible
- Filling slots with adjectives. “Inspiring,” “comprehensive,” “easy to read.” Nobody searches for those. They describe the book instead of matching a search.
- Repeating words already in your title. Amazon already indexes your title. Repeating those words in backend slots wastes precious characters that could be used to capture new searches.
- Single broad words. “Fitness” puts you against hundreds of thousands of books. “kettlebell workouts for women over 50” puts you against dozens.
- Guessing. The most common mistake of all: filling the slots at 11 PM on publish night with whatever comes to mind, then never touching them again.
Step 1: Mine Amazon’s Autocomplete
Go to Amazon, set the search dropdown to “Books” (or “Kindle Store”), and start typing a phrase related to your topic. Don’t press enter. Watch the suggestions.
Those suggestions are real searches by real buyers, roughly ordered by popularity. Type “journal for” and you’ll see who people are actually buying journals for. Type your topic plus each letter of the alphabet (“meal prep a”, “meal prep b”…) to pull out longer variations.
Spend 20-30 minutes here and collect every relevant phrase in a simple list. You want 15-25 candidate phrases before moving on.
Step 2: Confirm People Are Buying
A phrase being searched isn’t enough; you need proof that the searches turn into purchases. Search each candidate phrase and open the top several books in the results. Scroll to Product Details and check the Best Sellers Rank (BSR).
As a rough guide, books ranked under 50,000 sell steadily, and under 10,000 sell multiple copies a day. If the top results for a phrase all sit above 100,000, demand is probably too thin.
I covered how to read BSR in more depth in my guide to finding a Kindle niche that isn’t saturated, so I’ll keep it short here: you want several books under 50,000 ranking for your phrase.
Step 3: Check Whether a New Book Can Compete
Now look at those same top results through a different lens: could your book realistically join them?
- Encouraging signs: books ranking on page 1 with under 500 reviews, self-published books holding their own next to traditional publishers, older books (three-plus years) still ranking, and complaints in the 1- and 2-star reviews you could fix (outdated info, poor organization, missing topics).
- Discouraging signs: page 1 wall-to-wall with thousand-review bestsellers and big-publisher names. That phrase isn’t wrong; it’s just not winnable yet. Keep it as a backend keyword and choose a more specific phrase as your primary.
Step 4: Build Your Keyword Set
- Pick one primary phrase (searched, selling, winnable) and work it naturally into your title or subtitle. Naturally is the keyword; keyword-stuffed titles violate KDP’s policies and repel human buyers.
- Fill the seven backend slots with distinct phrases from your research list: variations, related searches, audience phrases (“gifts for new dads”), and problem phrases (“how to stop procrastinating”). No repeats of your title words, no need for quotes or commas tricks, and use the characters; a 50-character slot fits a whole long-tail phrase.
- Skip anything subjective or prohibited. “Best,” “new,” “free,” other authors’ names, and brand names you don’t own are all against KDP’s keyword guidelines and can get a book flagged.
Step 5: Revisit After Launch
Keywords are settings, not tattoos. After 30-60 days, check which searches are actually driving sales (your KDP reports and your book’s also-boughts give clues). Swap out slots that aren’t pulling weight for fresh phrases from your research list. Most authors never touch their keywords after publication day, which means small adjustments put you ahead of most authors.
A Note on Speed
Fair warning: done properly, this method takes a focused afternoon per niche. That’s fine for your first book or two. If you’re validating many ideas or publishing at volume, the manual approach becomes the bottleneck, and that’s a real cost worth weighing. (The same logic applies to niche selection itself, which I walked through in ” How to Find a Profitable Niche Without Spending Six Months on Research.)
Where to Go From Here
If you’re still deciding what to write about in the first place, I made a free guide that pairs perfectly with this method: How to Discover Profitable Non-Fiction Niches for Kindle Publishing.
It covers identifying niches with real demand, the tools worth using (including free ones), and the research mistakes that drain time and money before you publish. Grab it free here.
Keyword research isn’t the glamorous part of publishing. But it’s the part that decides whether anyone ever finds the glamorous part.
Match the words buyers type, and the 90% statistic becomes someone else’s problem.
