Solved

PDP A/B test: sticky "Add to cart" on mobile — worth doing?

Conversion OptimisationSolved

PDP A/B test: sticky "Add to cart" on mobile — worth doing?

Sara Khan·Asked May 26, 2026
Considering adding a sticky bottom "Add to cart" button on mobile PDPs. Our current PDP is long (image gallery, description, reviews, related products), and our scroll heatmap shows ~45% of mobile users scroll past the fold but never scroll back up to the ATC button. Has anyone A/B tested this? What kind of lift did you see, and any UX pitfalls (especially around the keyboard hiding/showing on quantity input)?

2 Replies

ACCEPTED ANSWER
Fix My Store Team·May 26, 2026
Tested this on 14 stores last year. Median lift in mobile add-to-cart rate: **+8.4%**, but with a wide range (-2% to +21%). The wins clustered in stores with: - Long PDPs (>2x viewport on mobile) - Single-variant products (no variant picker complexity) - Price < $80 (impulse range) Where it lost or did nothing: - Stores selling configurable products (apparel with size/colour). The sticky bar had to either show a small variant picker (cramped) or take users back to the top (annoying), and both performed worse than the static button. - Stores with high-intent buyers (B2B, expensive electronics) — the sticky bar didn't help, sometimes hurt because it crowded out the gallery. UX pitfalls to avoid: 1. **Don't show it until the user scrolls past the original ATC** — otherwise it's redundant and crowds the screen. 2. **Hide it when the mobile keyboard is open** — listen to `window.visualViewport` resize events, not `window.resize`. 3. **Respect iOS safe-area-inset-bottom** — otherwise it covers the home indicator on iPhones. Happy to share the Liquid + JS we used if it's useful.
Maya Iyer·May 26, 2026
Echoing this — we also saw it backfire on variant-heavy PDPs. A pattern that worked for us in that case: instead of a sticky ATC, we made the variant picker section itself sticky on scroll-up (just the variant row, not the whole top). Got us +6% on a fashion store without the "where am I" feeling of jumping back to top.