Content Engagement Analytics · July 2026
Scroll Depth vs Reader Progress
Scroll depth and Reader Progress both try to answer how far someone got. They don't measure the same thing.
What Is the Difference Between Scroll Depth and Reader Progress?
Scroll depth measures what percentage of the whole page a visitor scrolled past, including elements that aren't the article. Reader Progress measures the reader's position against four fixed points in the content specifically, detected through position rather than a percentage, so it isn't distorted by page layout the way scroll depth can be.
Both scroll depth and Reader Progress try to answer a version of the same question: how far did a reader get. They arrive at meaningfully different answers, because they measure different things.
How scroll depth works
Scroll depth tracks what percentage of the total page height a visitor has scrolled past, usually reported at fixed checkpoints (25%, 50%, 75%, 100%). It's measured against the whole page, which on most sites includes elements that aren't the article itself: navigation, sidebars, related-content modules, comment sections, footers. A percentage-based measurement inherits all of that noise, since the denominator is the full page, not the content.
Scroll depth also can't distinguish a fast, deliberate scroll to the bottom (checking length, jumping to comments) from a slow, complete read. Both register as 100% scrolled.
How Reader Progress works instead
Reader Progress uses four fixed milestones (Started Reading, Reached the Middle, Read Most, Reached the End) detected against the reader's position relative to the main content specifically, using the browser's own visibility detection rather than a scroll-percentage calculation. Each milestone fires once per page view, based on position reached, not scroll speed or scroll distance.
Why the difference matters in practice
Consider a long article with a large image gallery partway through. Scroll depth would show a big jump in percentage from a small amount of actual scrolling, since images take up more page height than text. Reader Progress, measuring against content position rather than raw page height, isn't distorted by that kind of layout variation in the same way.
Neither approach is "wrong" in an absolute sense. Scroll depth is simple, widely supported, and useful for some purposes. But if the question is specifically "how far into this content did readers get," milestone-based measurement answers it more directly than a page-height percentage does. See the glossary for the formal definitions of both terms.