EPUB vs KEPUB: what's the difference?

They look almost the same, and both work on a Kobo. But kepub is the format Kobo was built around, and it changes the reading experience in a few real ways.

EPUB

EPUB is the standard ebook format. Almost every reader and app understands it, from Apple Books to Google Play Books to Calibre. If you buy a book somewhere other than the Kobo store, it is almost certainly an epub. A Kobo can open an epub fine, so nothing is broken if you never convert.

KEPUB

KEPUB is Kobo's own version of epub. Underneath it is still an epub file, but Kobo adds some extra markup that its software uses. That markup is what powers the features people associate with a good Kobo experience:

• Accurate progress. The "time left in chapter" and "time left in book" estimates work properly on a kepub. On a plain epub they are often missing or rough.
• Real pagination. Page turns feel right and the page numbers behave, instead of jumping around.
• Faster rendering. Pages turn quicker, which is noticeable on longer books.
• Reliable highlights and bookmarks. These anchor to the right spot.

So should you convert?

If you read on a Kobo and you sideload your own books, converting to kepub is worth it. It is a one-step change that turns on the reading features the device already has. The content of the book does not change, only the formatting Kobo reads.

If you also read the same book on other devices or apps, keep the plain epub for those, since kepub is tuned for Kobo specifically. You can always convert back later.

The short version

EPUB is the universal format. KEPUB is the same book, formatted the way a Kobo likes it. On a Kobo, kepub reads better. Everywhere else, epub is what you want.