Sticky Add to Cart Button Example: Actual AB Test Results

Posted By Devesh Khanal

sticky add to cart button or not

Should you make your add to cart section sticky (that is, it stays visible when scrolling)?

In our work with dozens of ecommerce companies over the last 5 years, we’ve noticed that the design and UX of the add to cart section (buy buttons, options, quantity controls) is debated a lot.

  • Should you make the add to cart button sticky?
  • Should we make the entire section sticky?
  • Should we hide some selections (size, color, flavor) or show all?
  • Should we show all sizes as buttons or shove them in a dropdown?
  • In what order should we present the different options?

This case study is about the first question.

In this article, we present results from a simple AB test where we tested having the entire add to cart area be sticky versus not sticky on desktop devices for an ecommerce site in the supplement space.

The variation with the sticky add to cart button, which stayed fixed on the right side of the page as the user scrolls showed 7.9% more completed orders with 99% statistical significance. For ecommerce brands doing $10,000,000 and more in revenue from their desktop product page traffic, a 7.9% increase in orders would be worth $790,000 per year in extra revenue.

In our experience, sticky add to cart areas on desktop product pages are less common than on mobile, so this result suggests many ecommerce brands, marketing teams, and store owners may benefit from AB testing sticky add to cart buttons or entire add to cart areas being sticky on their product detail pages.

Note: If you’d like to run AB tests like this to help increase your ecommerce site’s conversion rate or improve user experience, you can learn about working with our ecommerce CRO agency here. Or if you want to read more case studies like this 

Building a Data Driven Culture: AB Tests Can Help Settle Endless Debates

The conference room: Where people typically debate things like this.

The conference room: Where the sticky add to cart button is likely debated non-stop with little useful progress is made.

When you read about AB tests online, most articles have a nice predictable pattern: (a) We had a great hypothesis. (b) we tested it (c) it worked and got a conversion lift!

But when you do enough AB testing (we run hundreds of AB tests on ecommerce sites every year), you come to learn that most tests don’t end up so neat and clean.

So instead, we urge you to think of an alternative, but also valuable use case of AB testing: 

Run a test to learn about your customers even when you could make arguments for either variation being “better” and there isn’t consensus on which one is “obviously going to win” (a phrase we often hear clients use).

Let’s use this article’s example to learn why this “ab tests for learning” use case is so useful: For this sticky add to cart button example, in the traditional design process, people in the company would debate in a conference room (or by email, or in Slack), about having a sticky vs. non-sticky add to cart area on their product page.

They’d go in circles fighting with each other about which is better, which is more on brand, which competitors do something similar, and on and on.

Then, either the higher ranking person wins or an executive steps in and gives their official decision like Caesar at the Colosseum (even though 99% of the time the executive is not a UX expert).

But in reality, neither side knows which will do better. Both arguments are legitimate. And the one important contingent that does not have a seat at the table is the customer. An AB test lets your customers give their input.

And, finally, whichever variation “wins” is important but not as important as the learnings about how your customer thinks, what they prefer, and what is more persuasive to them, all of which you could learn by simply running a test.

So, with all this on our minds, we ran this test.

The Variations: Fixed vs. Sticky Add to Cart Buttons

The variations were simple. One of them (A), the buy box was not sticky and in the other (B) it was sticky. (Aside: Read why we anonymize clients here.)

gummy vitamins AB

In this case, the client’s product page had a sticky buy box (variation B) to begin with, and it hadn’t yet been tested. The reason we decided to test this was because there was a content-focused culture around the brand, so we felt it was important to learn how much users want to be left alone to read content versus having a more in your face request to buy following them down the page.

One can make a theoretical argument for both variations:

  • Argument for variation A (not sticky): You don’t want the site to act like a pushy salesperson, hovering over your shoulder when you’re just trying to read about the product and its benefits. It will turn people off.
  • Argument for variation B (sticky): People can read about the product just fine, and reminding them of the ability to add to cart will increase the percentage of people that do so.

Results: Sticky Add to Cart Button Gets More Orders by 8%

In this test, the sticky add to cart variation showed 7.9% more orders from the product pages with 99% significance. The sticky version also showed an 8.6% increase in add to carts with 99%+ significance. The test ran for 14 days and recorded approximately 2,000 conversions (orders) per variation.

Referencing the arguments for either side above, this test gave the marketing department and us valuable information about the customer (and saved a potentially conversion hurting future change of undoing the sticky add to cart area).

Despite this brand’s heavy focus on content, despite the customers’ needs to read a lot about product uses, benefits, ingredients, and more, having an ever-present add to cart area seemed to be okay with the customer. It did not annoy the customers,  and in fact seems to increase the percentage of them that decided purchase. This is a useful learning, despite this test largely being in the usability category, not desirability.

(Note: This is true of this store, it may not be true of yours. Hence we always suggest at the end of case studies that you should “consider testing” this. We don’t say you should just “do” this.)

This learning can actually be extended beyond the product pages to content pages such as blog posts where we can test being more aggressive with product links and placements to see if similar results can be achieved there.

This is why we love using AB testing for learning.

Update: Sticky Add to Cart Button on Mobile Product Pages Also Increased Conversion Rate

Since first writing this case study, we tested multiple UX treatments for a sticky add to cart button on the mobile PDP of this exact same supplement ecommerce store. The smaller screen real estate on mobile devices, of course, means finding CTAs like the add to cart button can be more difficult, so making the add to cart button sticky could improve user experience.

We tested three variations: (A) No sticky add to cart button (B) Sticky add to cart button that simply scrolls the user to the add to cart area on the product page (C) Sticky add to cart button that causes the add to cart area to slide up from the bottom of the page like a hidden drawer.

gummy vitamins mobile

As of this writing, we’ve observed a 6.5% increase in orders for variation C where the add to cart area slides up like a drawer, with 97% statistical significance. This test has been running for 12 days and also has about 2000 conversion events (orders) per variation.

This suggests that similar conversion gains can be realized on mobile product pages, but the details of how to implement them and the UI/UX that will cause a conversion increase are important. Questions? Let’s discuss in the comments.

If you have questions about whether your store should test sticky add to cart functionality, how to execute it (e.g. Shopify plugins vs. manual coding), or about working with us, you can ask us in the comments, send us an email, or learn about working with us.

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