Sticky Add to Cart: What Mobile Tests Show

A sticky add to cart button keeps the purchase action on screen after the shopper scrolls past your theme's own button. On a phone, where a product page is a long column of photos, a description, reviews and shipping notes, that is a reasonable idea. Whether it earns more money is a separate question, and the published Shopify tests do not give one answer. This post reads four of them, including two that did not win, explains why the results differ, and ends with a setup and a measurement plan you can run on your own product pages. Every figure below comes from the test pages we link, and each of those pages reports the result in the agency's own words, with little or no statistical detail. Treat them as examples of what can happen, not as a forecast for your store.

What the tests actually reported

Two ecommerce agencies, Clean Commit and Blend Commerce, publish write-ups of the A/B tests they run on Shopify stores. Four of them concern a sticky add to cart. They are small in number and none is a controlled study, so we list what each one says and what it leaves out.

Read the table as a spread rather than an average. Two tests show a conversion lift, one shows a lift in conversion with a drop in revenue per visitor on phones, and one shows more add to cart clicks with fewer orders. That last pattern is the useful warning: a sticky button reliably creates more clicks, because it is always under the thumb, but a click is not an order. If the extra clicks come from shoppers who were not ready, the checkout rate falls and the headline metric hides it.

Why the same idea gives different results

The pages do not explain the differences, so what follows is our reading, not a finding.

The page decides how much there is to gain. A sticky button helps most where the real one scrolls out of view quickly. The Blend write-up for the apparel brand notes that on some product pages only 8.74% of visitors reached the add to cart button at all. On a short page, where the button is visible for most of the visit, a second copy has little to add.

What the bar says matters as much as where it sits. The AFTCO variant showed the price next to the button. A bar that says only "Add to cart" asks for a decision without the information the shopper needs to make it, so you may get clicks that turn into a variant error or an abandoned cart instead of an order.

Average order value moves too. AFTCO lost 2.5% on average order value while gaining on conversion, and Little Bible Stories lost revenue per visitor on mobile while conversion rose. A bar that makes it easy to buy one item quickly can pull shoppers past the section where you offer the matching add-on. If you run an offer below the fold, such as the ones in our product page upsell guide, look at order value before you call a test a win.

Where a sticky bar goes wrong

Four failure points come up often enough to check before you launch.

1. Two sticky buttons. Some themes ship their own sticky add to cart, and some stores add a second from an app. Shoppers then see two bars, or one covers the other. Turn the theme's version off in Theme settings before you add another.
2. A bar that covers something the shopper needs. A cookie notice, a chat button, a cart drawer or the on-screen keyboard can end up under or over a fixed bar. Check each on a real phone, in portrait and landscape, with the keyboard open in a form field.
3. Keyboard focus hidden behind the bar. WCAG 2.2 success criterion 2.4.11, Focus Not Obscured (Minimum), is a Level AA requirement. Its text is that when a component receives keyboard focus, it is "not entirely hidden due to author-created content." The W3C's explanation names sticky footers and sticky headers as the typical offenders and lists a sticky footer that completely hides a focused element as a failure. Tab through your product page with a keyboard on a narrow window and confirm that the focused control is never fully behind the bar.
4. Variants that do not follow the selection. If a shopper picks size M and the bar still says "Add to cart" for the default option, you will see errors and refunds, not sales. The bar must follow the selected option, show its price and say clearly when it is sold out.

Setting one up

If your theme has no sticky bar, or you want one you can switch on per device, the Sticky Add to Cart mini app is built for this. By its own page it appears after your theme's button leaves the screen, clicks your theme's own add button so a cart drawer or redirect still works the same, follows the option the shopper picks, and steps aside while the cart is open, while the keyboard is up and at high zoom. It is on for phones by default, and desktop is an option. Start with the template that shows the button with the photo, name and price, because the one test above that won clearly also showed the price.

Then run it as a test, not as a switch you flip and forget:

• Phones go in the test. Every published win above included a mobile result. A bar on a wide desktop screen is usually in the way.
• Keep one version without the bar. The same two weeks, the same traffic. The Blend apparel result was read after two weeks and still carries no significance figure, so treat that as a minimum for planning, not as proof.
• Judge by revenue per visitor and orders, not clicks. Add to cart rate rose in the inconclusive Clean Commit test while orders fell.
• Check average order value. If it drops, look at what shoppers stopped seeing on the page.
• Read by device. The Little Bible Stories device splits disagreed with each other, which is the reason to look at them separately.

Our attach rate guide and average order value guide show how to compute both measures from an order export, so you do not have to rely on the dashboard of a single app.

When to skip it

Skip a sticky bar when the button is already visible without scrolling on most of your pages, such as a single-product store with a short page. Skip it for a product where the shopper must read before buying, such as a supplement with a long set of warnings or a fit-sensitive item where the size guide is the decision. And skip it if your page already carries a fixed element a shopper needs, like a free shipping bar or a chat button, until you have tested how the two sit together on a small screen. The popup versus inline guide covers the same trade-off for offers.

Your next step

Pick your three highest-traffic product pages, check on a phone how far down the real button sits, and write down your current mobile conversion rate and revenue per visitor. Then switch on Sticky Add to Cart for phones against a version without it and read the result by orders and revenue per visitor after two weeks. You can start the trial from the mini app page, and the end-of-post template below builds a matching product page offer to test next to it.