The Ultimate Guide to EPUB Formatting for Amazon KDP (And Why MOBI Won’t Save You Anymore)

If you’ve spent any time in author forums lately, you’ve probably noticed a quiet but important shift: Amazon has been steering everyone toward EPUB, and the old “just upload a MOBI file” advice doesn’t hold up anymore. As of March 2025, Amazon stopped accepting MOBI files for fixed-layout eBooks entirely, which means a meaningful chunk of the formatting advice still floating around the internet is already outdated. If you’re prepping a manuscript for KDP right now, EPUB isn’t just the safer choice — for most book types, it’s the only one that makes sense going forward.

This guide walks through what EPUB actually is, why it’s become Amazon’s preferred format, and exactly how to get your file formatted correctly the first time, without the upload errors that send authors back to square one the night before launch.

What Makes EPUB Different From a Word Document

A Word document and an EPUB file might look identical on your screen, but underneath, they’re built on completely different logic. Word is a fixed-page format — every line break, every page number, every bit of spacing is locked into place exactly where you put it. EPUB is reflowable, which means the text reorganizes itself dynamically based on the reader’s device, screen size, and font preferences.

That reflow is the whole point. Someone reading your book on a 6-inch Kindle Paperwhite and someone reading it on a 10-inch iPad need the text to adapt to their screen, not be squeezed or stretched to fit a layout designed for paper. EPUB handles that natively because it’s essentially a structured package of HTML and CSS files, zipped together with a defined internal structure — chapters, headings, and navigation all tagged in a way that e-readers can interpret and rebuild on the fly.

This is also why manually formatting in Word and hoping for a clean conversion so often goes wrong. Word’s invisible formatting quirks — leftover styles, inconsistent spacing, manually resized text instead of proper heading tags — get carried into the conversion and can break navigation, mangle your table of contents, or trigger an outright rejection.

Why EPUB Has Become the Standard for KDP

A few things have pushed EPUB from “one of several accepted formats” to the de facto standard for serious self-publishers:

• MOBI is being phased out: Amazon has confirmed it will stop accepting MOBI for fixed-layout titles, and the broader trend points toward EPUB consolidating as the primary ebook format across the platform.
• Better structural consistency: EPUB’s reliance on proper heading styles (H1, H2, H3) means your table of contents, chapter navigation, and internal links are more likely to generate correctly and survive Amazon’s conversion process without manual cleanup.
• Cross-platform flexibility: A well-built EPUB doesn’t just work on Kindle — it’s the format accepted by Apple Books, Kobo, and most other major retailers, which matters if you ever decide to distribute beyond Amazon.
• More control over styling: Compared to a DOCX file that Amazon converts automatically, EPUB gives you direct control over the CSS, which means fonts, drop caps, scene breaks, and image placement behave the way you actually designed them to, not however Amazon’s converter interprets your Word formatting.

The Core Technical Requirements You Can’t Skip

Before you touch a single export setting, it helps to know exactly what Amazon is checking for. These aren’t suggestions — get any of these wrong and you’re looking at a bounced upload or a book that looks unprofessional once it’s live.

• Heading structure: Every chapter title needs to use a real heading style (Heading 1 or Heading 2), not manually bolded or enlarged text. This is what allows e-readers to build an accurate, clickable table of contents automatically.
• A functional table of contents: For most nonfiction titles, a working TOC isn’t optional — Amazon expects it, and a broken or missing TOC is one of the most common rejection triggers authors run into.
• Embedded, web-safe fonts: If your EPUB’s CSS references a custom font that isn’t properly embedded in the file package, Kindle devices will quietly substitute a default font, and any careful typographic choices you made will simply disappear on the reader’s screen.
• Image resolution: Interior images in an ebook should generally sit around 150 DPI — high enough to look sharp on a retina screen, but not so large that file size balloons unnecessarily. Cover files are a separate matter entirely and need to be much higher resolution.
• Clean, validated code: Before upload, run your EPUB through an EPUB validator (EPUBCheck is the standard tool) to catch malformed markup, broken internal links, or missing files inside the package — the kind of errors that are invisible in a casual read-through but will absolutely cause problems on certain devices.

Common Mistakes That Trigger Rejections or Bad Reviews

Most formatting problems trace back to a handful of repeat offenders:

• Manually resizing text instead of applying proper paragraph and heading styles, which breaks the reflow logic EPUB depends on.
• Mixing manual formatting with style-based formatting in the same document — this is one of the fastest ways to get unpredictable, inconsistent results once the file is converted.
• Skipping the preview step. A file that looks fine in your formatting software can still render with broken page breaks, missing fonts, or shifted images once it’s actually loaded onto a Kindle.
• Ignoring front matter structure. Title pages, copyright pages, and dedications need to follow the same structural logic as your chapters — sloppy front matter is often the first thing that signals “self-published” in the negative sense to a reader.

Should You Format the EPUB Yourself, or Hand It Off?

If you’re a technically inclined author publishing a single, text-only novel, doing it yourself with a tool like Vellum or Atticus is genuinely viable — those platforms handle a lot of the heading and CSS logic automatically. But the calculation changes fast for nonfiction books with complex TOCs, illustrated children’s books, books going into translation, or anyone planning a multi-platform release across Amazon, Apple Books, Kobo, and beyond. At that level of complexity, the time spent troubleshooting a single broken navigation file often costs more than just having it built correctly the first time.