Creep specifies the distance pages move away from the spine to accommodate paper thickness and folding in Saddle Stitch and Perfect Bound documents. InDesign considers the “cover” of the final piece to be the outermost printer spread, while the “centerfold” is considered to be the innermost printer spread. The term sheet represents two printer spreads: the front of the sheet and the back of the sheet. The creep increment is calculated by dividing the specified creep value by the total number of sheets minus one.

For example, a 16-page InDesign document could yield eight printer spreads, or four sheets. The front of the first sheet will consist of the first printer spread (pages 16 and 1) while the back of the first sheet will consist of the second printer spread (pages 2 and 15).

If the creep value in this example is 24 points (an exaggerated amount for the sake of clarity), the creep increment will be 8 points per sheet (24 divided by 3). The amount of creep applied to the outermost sheet will be 24 points, the amount of creep applied to the second sheet will be 16 points, and the amount of creep applied to the third sheet will be 8 points. No creep will be applied to the fourth and innermost sheet.

The amount of creep for each successive sheet is decreased by the creep increment. In summary, each page on the outermost sheet is moved 12 points (half of the 24-point creep value for this sheet) away from the spine, each page on the second sheet is moved 8 points (half of the 16-point creep value for this sheet) away from the spine, and each page on the third sheet is moved 4 points (half of the 8-point creep value for this sheet) away from the spine.