Many WooCommerce stores migrate to Shopify expecting immediate speed improvements, then discover their Shopify store is loading slower than their old WordPress site. The problem is almost always too many installed apps each injecting JavaScript. This guide covers how to achieve fast Shopify store performance after migration.

Understanding Shopify's speed advantage (and its limits)

Shopify's infrastructure advantages over self-hosted WooCommerce:

Global Fastly CDN: static assets (JS, CSS, images) served from the nearest edge node
Managed server infrastructure: no slow shared hosting, no server scaling issues
HTTP/3 support across all stores
Automatic image optimization: WebP conversion, size variants on demand

However, these advantages are easily negated by:

Every installed Shopify app injects JavaScript into your storefront (unless excluded)
Many merchants install 15–25 apps — each adds 50–200ms of JavaScript execution time
Large theme files with many unused sections
Unoptimized product images uploaded at massive file sizes

Shopify speed score

Shopify calculates a speed score (0–100) for each theme in Online Store → Themes. This is based on Google Lighthouse performance metrics for a simulated load on a median mobile device:

Score 80+: Fast. Green.
Score 50–79: Needs improvement. Yellow.
Score below 50: Slow. Red. Likely to impact conversion rate and SEO.

New Shopify store (Dawn theme, no apps): typically scores 85–95. After installing 10+ apps: often drops to 40–60. The apps are the primary degradation factor.

App script audit

The single highest-ROI speed optimization action: auditing and reducing installed app scripts.

How to audit app scripts

Open Chrome DevTools → Network tab → filter by "JS"
Load your Shopify store homepage
Identify every JavaScript file loaded: see domain names (apps load from their own CDNs like cdn.appname.com)
Match each script to an installed app
Google PageSpeed Insights → Diagnostics → "Eliminate render-blocking resources" — shows which scripts delay First Contentful Paint

Apps to audit for page load impact

Chat apps (Tidio, Intercom, Gorgias): live chat widgets load 100–300KB of JS. Load lazily or only on specific pages.
Review apps (Yotpo, Okendo): review widgets can be heavy. Ensure lazy loading is configured.
Loyalty/rewards apps (Smile, LoyaltyLion): add badges and widgets globally. Consider limiting to logged-in customers.
Wishlist apps: add JS to every product page. Evaluate load strategy.
Upsell apps (ReConvert, Frequently Bought Together): add JS to cart and product pages.
Popup/marketing apps: email capture popups load JS globally. Ensure they fire after page load, not before.

App exclusions

Most Shopify apps allow you to exclude them from specific page types (disable on homepage, only load on product pages, etc.)
Check each app's settings for "performance" or "load pages" settings
Some apps inject via theme.liquid (load on every page) and can't be easily limited — uninstall if not needed on all pages

Image optimization

Images are typically 60–80% of total page weight. Optimize aggressively:

Shopify's native image handling

Upload original files at full resolution (Shopify's CDN generates all size variants)
Shopify auto-serves WebP to supported browsers (all modern browsers)
Use Liquid image_url filter with width parameter: {{ product.featured_image | image_url: width: 800 }}
Use loading="lazy" on all below-the-fold images (most modern themes do this automatically)

Image compression before upload

Use TinyPNG or Squoosh to compress images before uploading to Shopify
Target: product images under 500KB at full resolution. Most photos can be 100–300KB at 2000px with minimal visible quality loss.
Shopify Image Optimizer apps (Crush.pics, TinyIMG): automatically compress images already in your Shopify Files

Hero images and banner images

Desktop hero images: 2000–2560px wide, 80–150KB (WebP/highly compressed JPEG)
Provide separate mobile hero images: 750px wide, lighter file size
Background images in CSS: convert to WebP and specify via picture tag with srcset

Theme optimization

Choosing a fast theme

Dawn (free): Shopify's reference theme. Built for speed. Consistently scores 90+. Recommended baseline.
Paid themes vary: many premium themes include animations, parallax, and JavaScript effects that reduce scores. Test speed before purchasing.
Shopify Theme Store: sort by "Speed" to see fastest themes in each category

Theme code optimization

Unused sections: most themes include sections you'll never use. These still load CSS/JS definitions.
Remove unused sections from theme code (or ask a Shopify developer to do so)
Inline critical CSS: the CSS for above-the-fold content should load first
Defer non-critical JavaScript: use defer or async attributes on non-critical scripts

Core Web Vitals targets

Metric	Good	Needs improvement	Poor
LCP (Largest Contentful Paint)	< 2.5s	2.5–4.0s	> 4.0s
INP (Interaction to Next Paint)	< 200ms	200–500ms	> 500ms
CLS (Cumulative Layout Shift)	< 0.1	0.1–0.25	> 0.25

LCP improvement (most impactful for Shopify)

The LCP element is usually your hero image or product featured image
Add fetchpriority="high" and remove loading="lazy" from the first above-the-fold image
Preload the LCP image: <link rel="preload" as="image" href="{{ featured_image }}">
Reduce LCP image file size as a priority over all other images

CLS improvement

Common Shopify CLS sources: font loading (FOUT), app widgets injecting layout, image dimensions not specified
Always specify image width and height attributes: prevents layout reflow when images load
Use font-display: swap for custom fonts (in theme settings or CSS)
Ensure app widgets (chat bubbles, loyalty badges) don't shift layout on load

Post-migration speed checklist

Run Shopify speed score baseline immediately after theme install, before adding apps
Install apps one at a time: re-run speed score after each to identify slow apps
Audit all app scripts: use Chrome DevTools Network → JS to identify all external scripts loading
Configure chat app to load lazily (fire 3 seconds after page load, not on DOMContentLoaded)
Compress all product images before upload: target under 300KB per image
Configure lazy loading on all below-the-fold images in theme
Add fetchpriority="high" to hero image on homepage
Enable lazy loading for review widget (typically in review app settings)
Remove or limit apps not providing measurable revenue impact
Run Google PageSpeed Insights on homepage, collection page, and product page
Set CWV monitoring: Google Search Console → Core Web Vitals report shows field data from real users

The most impactful single action for most Shopify stores is uninstalling unused apps. Merchants routinely install an app to test it, then forget to uninstall it when it's not needed — but the app's JavaScript continues loading on every page. Spending one hour auditing all installed apps, uninstalling unused ones, and checking that necessary apps load lazily can improve your Shopify speed score by 20–30 points and meaningfully improve LCP. This often produces better results than any amount of image optimization or theme tweaking.

Shopify store speed optimization after WooCommerce migration (2026)