When you set up a paperback on Amazon KDP, there is a small box that asks a big question: use a free KDP ISBN, or enter one you bought yourself? Clicking the free option is tempting, and for some books it is the right call. For others it quietly closes doors you only notice a year later, when you want your book in a bookshop or on another platform. This guide explains what each choice really means, the rules KDP applies, what an ISBN costs, and how to decide in five minutes.
KDP rules change from time to time. Everything below matches KDP's own help pages as we read them in November 2026, but check the current help pages before you publish.
The short answer
Use the free KDP ISBN if your paperback or hardcover will only ever be printed through KDP and you do not mind the publisher line reading "Independently published." Buy your own ISBN if you want your own imprint name on the book, if you might print the same edition anywhere else, or if you plan a series and want everything under one publishing name. For a Kindle ebook sold on Amazon, you do not need an ISBN at all.
The reason to decide carefully is simple: once a print book is published on KDP, the ISBN is locked. Changing your mind later means unpublishing and creating a new edition.
What an ISBN actually does
An ISBN (International Standard Book Number) is a unique identifier for one specific format and edition of a book. Bookshops, libraries, distributors and online stores use it to find and order the right version. It is not a copyright, it does not prove you wrote the book, and it does not put your book into bookshops by itself.
A few rules apply to every ISBN, free or bought:
- One ISBN per format. Your paperback and your hardcover each need their own number.
- New edition, new ISBN. KDP says the same ISBN cannot be reused for a new edition that introduces significant changes from the original. Fixing typos is not a new edition. Adding new chapters or rewriting large sections usually is.
- Ebooks and low-content books are the exceptions. On KDP, an ISBN is optional for ebooks and for low-content books such as journals and planners.
Free KDP ISBN vs your own ISBN at a glance
| Free KDP ISBN | Your own ISBN | |
|---|---|---|
| Cost | Free | You pay the ISBN agency in your country |
| Formats | Paperback and hardcover only | Any format, including ebooks sold elsewhere |
| Where you can use it | Only on KDP | KDP and any other printer or distributor |
| Publisher shown on Amazon | "Independently published" | The imprint name you registered |
| Who registers it | KDP registers it with Bowker using your book details | You register it with the agency and enter matching details in KDP |
| Low-content books | Not eligible | Allowed |
| KDP Expanded Distribution | Allowed | Allowed |
| Can it be changed after publishing? | No | No |
When the free KDP ISBN is the right choice
The free ISBN is not a trap. For many first books it is the sensible option. It usually makes sense when:
- You are publishing one book, on Amazon only, and have no plans to print it elsewhere.
- You are testing an idea, such as a short guide or a lead magnet for your business, and want to keep costs down.
- You are happy for the publisher field to read "Independently published."
- You still want the paperback offered through KDP's Expanded Distribution to bookstores and libraries. KDP accepts either a purchased ISBN or a KDP-assigned one for that program.
Getting one takes a minute. In your KDP Bookshelf, open the paperback or hardcover content page, go to the ISBN section, choose Get free KDP ISBN and click Assign ISBN. KDP handles the registration.
The money you save can go where readers notice it. A professional cover or a careful edit does more for sales than the name in the publisher field.
When buying your own ISBN is worth it
Buying your own ISBN costs money up front, but it keeps your options open. It is usually the better choice when:
- You want your own imprint. With a purchased ISBN, the book's detail page shows the imprint you registered, such as your company or brand name. Coaches, consultants and business owners often want this because the book carries their business name rather than a generic label.
- You may print the same edition elsewhere. KDP is clear that free ISBNs can only be used on KDP. If you later want the same paperback through another print-on-demand service, a library supplier or a local printer for event copies under that same number, you need an ISBN you own.
- You are planning a series or several books. A block of ISBNs is far cheaper per number than buying them one at a time, and every book appears under the same publisher name.
- You sell your ebook outside Amazon. KDP does not need an ebook ISBN, but some other stores and library platforms ask for one.
What an ISBN costs
ISBNs are sold by one official agency per country or region, and prices vary a lot depending on where you live.
- United States: Bowker is the official ISBN agency. At the time of writing, its store lists a single ISBN at around $125 and a block of ten at just under $300. KDP's help pages also mention that Bowker offers discounted rates for KDP authors. Check Bowker's current price list before you buy.
- Other countries: you buy from your own national agency, and you should register the ISBN in the country where you, the publisher, are based. Some agencies charge, and some national agencies issue ISBNs free of charge, Canada's being a well-known example.
The math for US authors is simple. If your book will have a paperback and a hardcover, and perhaps an ebook sold outside Amazon, you already need two or three numbers. A block of ten costs about the same as two or three singles and leaves numbers for future books.
One warning: buy from the official agency, not from a reseller offering cheap single ISBNs. An ISBN is tied to the publisher who registered it, so a number bought through a third party can end up listing that third party as the publisher of your book.
A quick decision guide
Answer these five questions honestly:
- Is this an ebook only, sold on Amazon? You do not need an ISBN. Stop here.
- Will the print edition only ever be sold through KDP? If yes, the free ISBN is fine. If you are not sure, treat it as a no.
- Do you want your name or business as the publisher? If yes, buy your own.
- Are you planning more than one book or more than one format? If yes, a block of ISBNs is usually the better value.
- Would it bother you to lose the option of other printers or distributors later? If yes, buy your own now, because switching after publication means a new edition.
Here is how that plays out in practice. These are illustrations, not real clients:
- A retired teacher publishing a family memoir for relatives and a few readers on Amazon: a free KDP ISBN for the paperback is perfectly sensible.
- A business coach using a book to win speaking work and clients: buy a block, register the coaching business as the imprint, and use separate ISBNs for the paperback and the hardcover.
- A novelist starting a trilogy who wants to sell signed copies at events and may go wide later: buy a block now so all three books, in every print format, sit under one imprint.
How to use your own ISBN on KDP without errors
Most ISBN problems on KDP come from small mismatches. KDP checks the details you type against the record held by the ISBN agency, and if anything differs, you will not be able to publish. Follow these steps in order:
- Register the ISBN first. In your agency account, assign the number to the book and fill in the exact title, subtitle, author name, format (paperback or hardcover) and imprint.
- Decide the imprint name once. Pick the publishing name you will use for every book. KDP's imprint field allows up to 100 characters.
- Copy and paste, don't retype. KDP recommends copying the details straight from the agency. The fields are case-sensitive, and even an extra space at the end of the imprint name can cause a mismatch error.
- Enter it in KDP. In your Bookshelf, open the paperback or hardcover content page, choose Add your own ISBN in the ISBN section and enter the number and imprint.
- Never use placeholders. Do not type "unknown" or "n/a" in the imprint field.
- Wait after edits. If you change your ISBN record at the agency, KDP says it can take up to five business days to pick up the change. Save your KDP updates after that.
- Let Amazon place the barcode. If you add your own barcode to the cover, it must match the ISBN exactly, and any price code should match your list price. KDP recommends letting it place a barcode on the back cover for you, at no extra cost, which avoids validation errors at upload.
If KDP shows "Please fix the highlighted issue" but no field is highlighted, it is usually the ISBN or imprint. Compare the title, author and imprint letter by letter with your agency record.
Already published with the free ISBN?
This is the situation many authors find themselves in, and the honest answer is that there is no quick switch. KDP does not allow ISBN changes once a book is published. To move to your own ISBN, you would unpublish the existing paperback and publish it again as a new edition with the new number and imprint.
A new edition is a new product page, so plan the switch rather than doing it on impulse. Some authors leave the original free-ISBN edition alone and use their own ISBNs for new formats or future books instead. If you do switch, our KDP book launch checklist helps you plan the new edition like a small relaunch.
If your book is still a draft, you are in luck. You can change the ISBN freely until you click publish. KDP even notes that if you want to free up a purchased ISBN from a draft to use on another book, you can switch that draft to the free KDP ISBN option.
Common ISBN mistakes to avoid
| Mistake | What happens | What to do instead |
|---|---|---|
| Using one ISBN for paperback and hardcover | Not allowed, each format needs its own | Assign a separate number to each format |
| Clicking "free ISBN" without thinking about other printers | The number only works on KDP and cannot be moved later | Decide before publishing, not after |
| Retyping the imprint by hand | Case or spacing mismatch blocks publishing | Copy and paste from the agency record |
| Buying a single ISBN from a reseller | The reseller may appear as the publisher | Buy from your country's official agency |
| Editing the agency record and saving KDP straight away | Errors until KDP picks up the change | Wait up to five business days |
| Thinking an ISBN protects your work | It doesn't, it is only an identifier | Read up on copyright separately |
On that last point, copyright and ISBNs are often confused. Your copyright exists whether you use a free or a purchased ISBN. If you want the extra protection of registration, our guide on how to copyright a book explains the steps.
ISBNs and ghostwritten books
If a ghostwriter has written your book, the ISBN choice works exactly the same way. The book is published under your name, in your KDP account, and you decide whether the publisher line shows "Independently published" or your own imprint. Make sure the author name on the ISBN record matches the name on the cover and in KDP exactly.
Your ISBN checklist
- I know which formats I am publishing (ebook, paperback, hardcover).
- I know whether the print edition will ever be printed or sold outside KDP.
- I have decided whether I want "Independently published" or my own imprint.
- If buying, I am buying from my country's official ISBN agency.
- Each format has its own ISBN.
- The title, subtitle, author and imprint match exactly between the agency and KDP.
- I am letting KDP place the barcode, or my barcode matches the ISBN exactly.
- I have made the decision before clicking publish, not after.
Once the ISBN is sorted, the rest of the setup is easier. Our guides to self-publishing on Amazon KDP, choosing KDP categories and keywords and KDP royalties cover the next steps.
Frequently asked questions
Is the free KDP ISBN good enough?
Yes, if your paperback or hardcover will only ever be printed and sold through KDP. The free ISBN works for Amazon and for KDP Expanded Distribution. Its limits are that the imprint shows as "Independently published" and the number cannot be used with any other printer or distributor.
Do I need an ISBN for a Kindle ebook?
No. KDP does not require an ISBN for ebooks, and Amazon identifies the Kindle edition with its own ASIN. You only need an ebook ISBN if you plan to sell the same ebook through other stores that ask for one.
Can I change my ISBN after my book is published on KDP?
No. KDP does not allow an ISBN change on a published book. You would need to unpublish it and publish a new edition with the new ISBN. While the book is still a draft, you can switch between a free and a purchased ISBN.
Can I use the same ISBN for my paperback and hardcover?
No. Each format needs its own ISBN, so a paperback and a hardcover need two different numbers. A new edition with significant changes also needs a new ISBN.
Does owning my ISBN mean I own the copyright?
No. An ISBN is a product identifier, not a legal right. Copyright exists in your writing whether you use a free or a purchased ISBN. Registration with your national copyright office, where available, is a separate step.
Why does KDP say my ISBN or imprint does not match?
KDP checks the title, author and imprint you enter against the record held by the ISBN agency, and the check is case-sensitive. Copy and paste the details from your agency account, remove extra spaces, and if you have just edited the record, wait up to five business days for KDP to pick up the change.
Want help setting up your book on KDP?
The Authors Prime has published 500+ books, and our services start from $200. Our Amazon KDP publishing team can help you choose between a free and a purchased ISBN, set up your imprint details so they match, and get your formatted interior and cover through review without errors. Any prices we discuss are general guides, not quotes, until we have seen your project. Book a free consultation or call us at +1 205-301-7751. There is no obligation.