If we could make exactly one change to the average Shopify store's mobile experience, it would be this: a sticky Add to Cart bar.

The problem it solves

On a phone, your product page is a long scroll: gallery, badges, variants, description, reviews. The Add to Cart button lives near the top — and the moment a shopper scrolls down to read (which interested buyers do!), the button is gone. To buy, they must scroll back up and find it.

That sounds like a tiny inconvenience. At scale it isn't: the shoppers who scroll deepest are your most interested ones, and they're the ones you make work hardest to give you money. On stores we've audited, product pages where the buy button is off-screen for most of the visit reliably underperform.

What a good sticky bar includes

A slim bar pinned to the bottom of the viewport once the original button scrolls away:

  • Product name (truncated) + price — reassurance they're buying the right thing
  • The selected variant — synced with the picker above, never out of step
  • One button: Add to Cart — the same action, always reachable

That's all. It should appear only after the original button leaves view, never cover content when the keyboard is open, and respect iPhone safe areas (the home-bar zone).

The mistakes that ruin it

1. A second, competing state. If the sticky bar has its own variant selector that can disagree with the page's picker, you will sell people the wrong size. One source of truth, always.

2. Blocking the view. A bar taller than ~60px, or one that stacks with a cookie banner and a chat widget, eats a third of a phone screen. Shoppers close what crowds them.

3. Loading it via a heavy app. There are apps that do this — many inject surprisingly large scripts on every page to render one button. If your theme can do it natively (most modern ones can, or a developer adds it in a day or two), you get the benefit without the speed tax.

4. Desktop parity for its own sake. On desktop the buy button is usually visible anyway; a sticky bar there adds clutter for nothing. Ship it mobile-first.

How to add one

  • Check your theme first: many 2024+ themes (Dawn-family included) have a "sticky add to cart" toggle buried in theme settings → product pages. Free if it's there.
  • Small theme edit: for a developer, this is a contained job — a snippet, a scroll listener (or IntersectionObserver), and careful variant syncing. Days, not weeks.
  • App as last resort: if you must, pick one, test your speed score before and after, and uninstall ruthlessly if it costs more milliseconds than it's worth.

How to know it worked

Measure add-to-cart rate on mobile for two weeks before and after (GA4: add_to_cart events ÷ view_item events, mobile segment). This metric moves fast and doesn't need purchase volume to read.

Is this YOUR store's biggest leak?

Maybe — it's the most common one we find. But "most common" isn't "yours": some stores' worst leak is a 5-second cart redirect, dead tracking events, or reviews that never render.

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Not sure which of these is hurting YOUR store? We built a free tool that checks all of it automatically — it crawls your store the way a real shopper does (on a phone, from first visit to checkout) and sends you a report naming your actual products and pages, in about 15 minutes. [Get your free store audit →](/free-audit)

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One fix, done properly, beats five done half-way. Start with whatever your data says is actually costing you the most.