Shopify Speed Checklist: Faster Mobile Pages and a Smoother Checkout (2026)

A slow Shopify store is rarely one big problem. It is usually a pile of small ones: oversized images, code left behind by apps you uninstalled years ago, third-party scripts that block rendering, and a cart that makes shoppers work too hard. This checklist goes through them in the order that usually pays off, on mobile, where most shoppers are.

It is the same checklist App369 works through in its fixed-price Shopify Speed & Checkout Tune-Up. Every change below can be made on a duplicate theme and checked before you publish it.

Step 1: Measure before you change anything

Pick four URLs that matter: the home page, a busy collection, a best-selling product, and the cart. For each one:

• Run PageSpeed Insights on mobile. If Google has enough real-user data for your store, the top of the report shows your Core Web Vitals from the Chrome UX Report. That field data is what Google uses; the Lighthouse score below it is a lab test.
• Run Lighthouse three times and keep the median. Single runs vary a lot.
• Write the numbers down. Without a baseline, you can't tell whether a change helped.

The three Core Web Vitals and their "good" thresholds are:

Step 2: Images

Images are the most common cause of a slow LCP on Shopify.

• Serve the right size. Use Shopify's image_url filter with a width, and image_tag with widths and sizes, so a phone downloads a phone-sized image instead of a 4,000-pixel original.
• Load the hero image first. The main image above the fold should not be lazy-loaded. Give it fetchpriority="high" so the browser fetches it early.
• Lazy-load everything below the fold. Product grids, reviews and footer images can wait.
• Set width and height. Images without dimensions push content around as they load, which hurts CLS.

Step 3: Leftover app code and third-party scripts

Uninstalling a Shopify app doesn't always remove what it added to your theme. Older apps often pasted snippets into theme.liquid or product templates, and those keep loading after the app is gone.

• Search the theme code for the names of apps you no longer use, and remove their snippets on the duplicate theme.
• List every script that loads on the product page (the Network tab in Chrome DevTools shows them). For each one, ask whether it still earns its keep.
• Load chat widgets, review carousels and pop-ups after the page is usable, not before.
• Keep tracking pixels you rely on. Removing one breaks reporting, not just a script.

Step 4: Fonts

• Use one or two font families, and only the weights you actually show.
• Prefer fonts from Shopify's font library or system fonts; they load from Shopify's CDN.
• Use font-display: swap so text appears immediately in a fallback font.

Step 5: Liquid on collection and product pages

Heavy Liquid slows the server's response before the browser even starts. The usual suspects are loops over every product in a large collection, nested loops over variants and metafields, and the same snippet rendered many times. Shopify's Theme Inspector for Chrome shows which Liquid takes the longest to render, so you can fix the slowest part first.

Step 6: Layout shift

CLS problems on Shopify usually come from announcement bars, discount banners and app badges that appear after the page loads, and push everything down. Reserve their space in CSS, or render them in the theme instead of injecting them with a script.

Step 7: From cart to checkout

Speed doesn't help if the cart is hard to get through. Check, on a phone:

• Express checkout. Shop Pay, Apple Pay and Google Pay buttons (Shopify's dynamic checkout buttons) let returning shoppers skip typing. Show them where your theme supports it.
• The cart drawer. It should open quickly, show the total clearly, and let shoppers change quantities without reloading.
• No surprises. Shipping costs and the returns policy should be visible before checkout, not discovered in it.
• App injections. Upsell and gift-wrap apps that add steps or slow the cart are worth testing with and without.

Shopify's checkout pages themselves can only be customized in limited ways, and most deeper changes need Shopify Plus. Everything up to the checkout is in your theme, which is where most of the friction usually is.

Step 8: Measure again, then publish

Run the same four URLs, three times each, on the duplicate theme, and compare with your baseline. Keep a short log of every change, so if something looks wrong after publishing you know exactly what to undo. Lab scores move faster than field data: Core Web Vitals in PageSpeed Insights reflect the last 28 days of real visits, so give them a few weeks.

When to get help

If you'd rather not spend a week in theme code, App369 does this as a fixed-price tune-up for $750, delivered in 5 business days. You get the baseline and after numbers for four page types, the fixes on a duplicate theme you review and publish yourself, a cart-to-checkout review, and a log of every edit. App369 never publishes to your live store or touches payment or customer data. Thinking about leaving Shopify instead? Read Shopify vs custom e-commerce development first.

Frequently Asked Questions

Why is my Shopify store slow on mobile?

Usually because of oversized images, scripts left behind by uninstalled apps, third-party widgets that load before the page is usable, and heavy Liquid loops on collection pages. Phones have slower processors and networks, so these problems show up there first.

Does the Shopify speed score affect sales?

Speed affects how quickly shoppers can see and use your pages. A faster store doesn't guarantee more sales, but slow product and cart pages give shoppers more chances to leave. Measure your own before-and-after numbers rather than relying on a general promise.

Do uninstalled Shopify apps still slow down my store?

They can. Older apps often added code to the theme files, and uninstalling the app doesn't always remove it. Search your theme for the app's name and remove leftover snippets on a duplicate theme first.

Can I make speed changes without risking my live store?

Yes. Duplicate your theme, make and test every change on the copy, compare the numbers, and publish the copy only when you are happy with it. You can switch back to the old theme if anything looks wrong.

Can I customize the Shopify checkout page for speed?

Only in limited ways. Most checkout customization beyond Shopify's settings needs Shopify Plus. The cart page, cart drawer and express checkout buttons are part of your theme, and that is usually where friction can be removed.