# 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.

- Source: https://bixlow.com/en/ideas/sticky-add-to-cart-on-mobile
- Language: en
- Updated: 2026-11-02
- Publisher: Bixlow

## 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.

1. In the variant, once the original button scrolls off screen, a fixed bar appears at the bottom with the price and “Add to cart”.
2. 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.
3. Make sure the bar doesn't cover anything important, such as the chat button or the cookie notice.
4. 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._


> **When I would not test it.** If your theme already has a sticky bar, there is nothing to test. And if your product pages are so short that the button rarely leaves the screen, the bar will hardly ever appear.


## FAQ

### Isn't a fixed bar annoying?

It can be, if it is tall or covers content. Keep it slim, with the price and the button, and hide it while the original button is visible.

### What about desktop?

On desktop the product page usually fits almost entirely and the button gets lost less. Start with mobile, where the problem actually exists.

### What about products with variants?

If no size is picked, the bar takes the shopper to the selector. What must not happen is a tap followed by an error they don't understand.

## Further reading

- [Next idea: open search bar on mobile](https://bixlow.com/en/ideas/open-search-bar-on-mobile)
- [How to write a CRO hypothesis](https://bixlow.com/en/glossary/cro-hypothesis)
- [Sample size calculator](https://bixlow.com/en/tools/sample-size-calculator)