Sticky add-to-cart bar on mobile: +10% conversion, not significant
Test run byBlend CommerceCRO agency
Commentary byLiftArchiveOur analysis, not theirsA sticky add-to-cart bar on PerTronix mobile product pages showed a 10% conversion rate lift, but the result was not statistically significant, so we treat it as inconclusive.
Blend Commerce ran the A/B test for the automotive parts brand.
Add-to-cart rate also fell 20%, which pulls in the opposite direction.
- Conversion rate: +10%, but not statistically significant. Blend reported the trend held over an extended test period.
- Add-to-cart rate: -20%. Fewer shoppers added items, which is a negative signal.
- Cart clicks: +5%. Slightly more visits to the cart.
- Bounce rate: -3%. A small improvement in shoppers leaving straight away.
- Inconclusive overall: the headline lift could be noise, and the metrics disagree with each other.
The change
The variant adds a sticky add-to-cart bar with a details button on mobile.
Simplified mockup drawn by LiftArchive from the shared screenshots.
Control
The mobile product page had the add-to-cart button only near the top. Shoppers who scrolled down to read reviews had to scroll back up to buy.
Variant
A sticky add-to-cart bar stayed on screen as shoppers scrolled, with a second button to view product details.
Why it likely came out this way
Our reading of the result, not the practitioner's claim.
- Keeping the buy button in reach removes the scroll back up after reading reviews, which should help shoppers who are ready to buy.
- The details button may have pulled some shoppers into reading more before adding, which could explain the drop in add-to-cart.
- Automotive parts often need fit checks, so the buying decision may depend more on product data than on button placement.
Caveats: The result did not reach statistical significance despite an extended run, and add-to-cart rate fell 20%. Sample size and exact duration were not shared. Blend still shipped the variant.
Who ran it
Blend Commerce ran this test for PerTronix and published the results (Blend Commerce A/B test). The numbers are theirs; the summary and commentary on this page are ours.
Read the original case study on Blend Commerce →
How to run this test on your store
- Hypothesis
- If we add a sticky add-to-cart bar on mobile product pages, then more shoppers will buy because they will not need to scroll back up after reading reviews.
- Primary metric
- Mobile conversion rate
- Guardrails
- Add-to-cart rate
- Revenue per visitor
- Return or cancellation rate
- Who should test it
- Stores with long mobile product pages where reviews or specs sit far below the buy button. Plan for enough traffic to reach significance, since this test did not.
Questions
Does a sticky add-to-cart button increase conversions?
It often helps on long mobile pages, but results vary.
In this test the conversion lift was not significant and add-to-cart rate fell, so the evidence here is mixed.
Why would add-to-cart fall while conversion rises?
Fewer but more committed shoppers may be adding items.
It can also simply be noise when a test has not reached significance.
Should a sticky bar show on desktop too?
Most sticky bars are aimed at mobile, where the buy button scrolls out of view fastest.
Test desktop separately if you try it there.
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