Free Book Subtitle Generator (+ Guide)
A book subtitle generator that keeps your title and writes the promise, at the length your genre's bestsellers use.
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by Navid Moazzez·Updated Sept 30, 2026·3 min read·Navid.me is reader-supported. When you buy through links on this site, I may earn an affiliate commission. Learn more.Embed this tool on your site
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This free book subtitle generator keeps your title and writes the subtitle: the line that says what the book does for the reader.
It's built on how 869 New York Times bestsellers are titled. In nonfiction, a subtitle is the rule, not the exception, and it has a usual length.
Here's how many bestsellers carry one, how long they run, and the rules KDP applies to them.
TL;DRKey takeaways
What is a book subtitle?
A book subtitle is the line after the title that says what the book is about or what the reader gets, like "Shipping Creative Work" under Seth Godin's The Practice.
KDP calls it "a subordinate title that contains additional information about the content of your book."
How many bestsellers have a subtitle?
Most nonfiction does:
- With a subtitle
- 86%
- Subtitle length (middle half)
- 6 to 10 words
- With a subtitle
- 84%
- Subtitle length (middle half)
- 5 to 10 words
- With a subtitle
- 71%
- Subtitle length (middle half)
- 6 to 10 words
- With a subtitle
- 57%
- Subtitle length (middle half)
- 5 to 9 words
All 14 history bestsellers in the set have one, at 5 to 9 words.
These numbers are for nonfiction. In fiction, the line under the title is usually a series name, not a promise.
What a good subtitle does
Among the bestsellers, a subtitle does one of 3 jobs:
- States the promise: Slow Productivity: The Lost Art of Accomplishment Without Burnout.
- Names the method: Be Useful: Seven Tools for Life.
- Sets up the story: Going Infinite: The Rise and Fall of a New Tycoon.
The generator writes all 3 kinds, so you can see which one fits your book.
Where a long subtitle gets cut
In Amazon's search results, the title and subtitle share a few lines under the cover:
- The cover at search size, where the subtitle is usually the smallest words on it.
- The title and subtitle, cut to 3 lines in this grid. A long subtitle loses its end here.
The generator keeps subtitles to your genre's usual length, so less of yours is cut.
KDP's subtitle rules
KDP applies the same rules to a subtitle as to the title, and counts them together:
- Title and subtitle at 200 characters or more
- Sales rank words, like "bestselling"
- Promotion words, like "free"
- Repeated generic words, like "notebook" or "journal"
- HTML tags
How to use the book subtitle generator
Your pitch is kept in your browser, and the title, description and outline generators use it too.
Who is the book subtitle generator for?
It's for authors whose title needs a promise under it:
- Book title generator – anyone still choosing the title
- Book description generator – authors writing the pitch
- Headline analyzer – anyone testing the words
- Amazon book description formatter – authors finishing their Amazon page
More tools like these are on my free tools page.
Book Subtitle Generator FAQs
Questions about book subtitles? Here's what to know.
A book subtitle is the line after the title that says what the book is about or what the reader gets.
KDP calls it a subordinate title with more information about the book's content.
Most nonfiction bestseller subtitles run 5 to 10 words; in business and self-help, the middle half is 6 to 10 words.
On KDP, the title and subtitle together must be under 200 characters.
No, but most nonfiction bestsellers have one: 86% of business, 71% of self-help and 57% of memoir bestsellers in the set carry a subtitle.
A subtitle can use the words readers search for, as long as it follows KDP's title rules: no repeated generic words, no sales rank words and no promotion words.
Yes, the book subtitle generator is free, with no sign-up.
Asking your own AI is free, and Generate here has a daily limit.
The book title generator finds the title first, and the book description generator works from the same pitch.
See all my free tools.
I did. I'm Navid Moazzez, and I made the book subtitle generator as one of my free tools on navid.me.
More about me.
Navid Moazzez
AI business strategist
Navid Moazzez helps creators and founders master AI and build their own AI Operating System (AI OS) to automate their business and life.
Navid.me is reader-supported. When you buy through links on this site, I may earn an affiliate commission. Read the affiliate disclaimer.
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