Keep the add-to-cart in reach on long pages
Use a sticky add-to-cart only when a long PDP creates a reachability problem, then verify variant accuracy and viewport safety.
Skip this if
- Short product pages where the primary buy box remains easy to reach
- Mobile viewports already crowded by unresolved fixed elements
Content-rich product pages answer real objections below the fold, and that is where a lot of the convincing happens. The side effect is that the only add-to-cart often sits thousands of pixels above the place where the shopper actually decides.
The decision: on long product pages, especially mobile, add a sticky add-to-cart bar that appears after the main buy box scrolls out of view. No large-scale public research establishes that sticky bars lift conversion. This is a conditional operating recommendation based on a reachability problem you can verify on your own page, and it is something to test rather than assume.
The rest of this lesson is available once the Atlas is unlocked.