A/B test: a sticky add to cart button on mobile
If the add to cart button on the mobile product page stays fixed at the bottom while scrolling, then add to cart will rise, because the button is within reach when the shopper decides, not three screens up.
By Fernando Blanco Dosil · Updated November 2, 2026
Why it can work
On a phone, the product page is long: photos, price, button, description, sizes, reviews. The shopper reads, scrolls, checks the reviews, and that is when they make up their mind. By then the button is way back at the top.
Scrolling back up isn't hard, but it is a moment where anything can happen: a message comes in, they have second thoughts, they leave it for later. With the button fixed at the bottom, the decision and the tap happen in the same second.
How to set it up
In Bixlow you describe the change to the agent, it builds it on your site and launches it as an A/B test once you approve it. A/B tests are on the paid plans, starting with Standard.
- In the variant, once the original button scrolls off screen, a fixed bar appears at the bottom with the price and “Add to cart”.
- If the product has sizes or colours and none is picked, tapping the bar takes the shopper to the selector instead of showing an error.
- Make sure the bar doesn't cover anything important, such as the chat button or the cookie notice.
- Run it on mobile only, across all product pages.
What to measure
| Metric | |
|---|---|
| Primary metric | Add to cart per product page visitor on mobile |
| Metric that must not get worse | Orders per visitor on mobile |
| Where it is measured | Clicks on either add to cart button |
Count clicks on the original button and the bar together; if you only count the bar, the variant will always look like it wins.