In printing terms, "creep" refers to the inner pages of a saddle-stitched booklet that stick out a bit more than the outer pages. This happens because the edges of the inner pages are narrower when the pages are folded and bound.
If you don't think about creep when designing, it can create issues for page numbers and borders, bringing the elements closer to the outer edge and not looking as intended.
The amount of creep depends on how many pages are in the booklet and how thick the paper is. Designing for creep means adjusting the content to make sure the outer margins stay consistent, especially in booklets with lots of pages.
If your booklet has less than 40 pages, creep usually isn't a big deal and doesn't need fixing. But in thicker booklets, you need to move the content further away from the edge to compensate for the creep. Thicker paper makes this shifting more necessary.
Designers need to know that inner pages have more creep than outer pages when dealing with saddle-stitch creep. When moving graphics and text around, keeping enough space at the edges is super important to avoid important elements getting too close to the booklet's edge.
Tip: If you are looking to produce a high-page count booklet and are worried about the effects of creep, we suggest that you opt for a Perfect Bound Book. The way that this book is constructed reduces the risk of creep affecting your content.