LCP in Shopify Themes: Making It Fast Without Losing Your Sanity
Why LCP Matters (And Why It’s Often Slow)
LCP (Largest Contentful Paint) is one of those fancy Core Web Vitals that Google cares about—and if Google cares, we have to care. A slow LCP makes your Shopify store feel sluggish, frustrates users, and can hurt SEO rankings.
A snappy LCP keeps shoppers happy, improves conversions, and makes your site feel instant. But in Shopify, we often run into:
- 🖼 Images loading too late (your hero section takes its sweet time showing up)
- 🏗 CSS & JavaScript blocking rendering (the browser is stuck waiting instead of painting the page)
- 🎨 Unoptimized fonts & Shopify apps adding unnecessary delays
How to Measure LCP Correctly
Before optimizing LCP, you need good data—and where you get that data makes a big difference:
✅ Performance Tab (Chrome DevTools) → Shows real-world data based on actual page load behavior.
✅ Lighthouse Tab → Runs a simulated test in a controlled environment to estimate performance.
💡 You can throttle both tabs to simulate mobile devices or slower internet speeds. But I rely more on Lighthouse for simulated data, while the Performance Tab is great for understanding what’s really happening.
What an Optimized LCP Should Look Like
In a perfectly optimized world, your LCP timing should roughly break down like this:
| Metric | Target % | What It Means |
|---|---|---|
| TTFB (Time to First Byte) | 40% | Time Shopify’s server takes to respond |
| Load Delay | 10% | Time before the browser starts loading the LCP element |
| Resource Download | 40% | Time to fully load the LCP element |
| Render Delay | 10% | Time the browser spends processing before displaying the LCP |
Key Fixes for Each Stage:
- Load Delay: Use
fetchpriority="high"(if nosrcsetis used). - Resource Download: Optimize images (WebP, AVIF, compression).
- Render Delay: Reduce render-blocking CSS & JavaScript.
Fixing LCP Bottlenecks in Shopify Themes
1. The Simple But Effective Fix: fetchpriority="high" on the LCP Image
✅ Helps the browser recognize that this image is important and should be loaded ASAP.
✅ Doesn’t work with srcset—browsers ignore fetchpriority="high" when srcset is used.
<img src="hero.jpg" fetchpriority="high" width="1200" height="600" alt="Hero Image">
2. Lazy Loading – When to Use It & When NOT to Use It
❌ Do NOT lazy load your LCP image—this increases Load Delay since the browser won’t fetch it early.
✅ Use lazy loading for images that aren’t immediately visible, like:
- Below-the-fold images
- Images hidden in mega menus, sliders, or popups
<img src="product.jpg" loading="lazy" width="500" height="500" alt="Product Image">
3. Optimizing Image Load Time
✔ Convert images to WebP or AVIF for smaller file sizes.
✔ Compress images properly without losing quality.
4. Preloading Fonts
✔ Fonts can delay LCP because text elements depend on them.
✔ Preload key fonts to avoid delays:
<link rel="preload" href="your-font.woff2" as="font" type="font/woff2" crossorigin="anonymous">
✔ Use font-display: swap so text appears even if fonts take a second to load.
5. Reducing Render Delay (The Hardest Part)
❌ Blocking CSS and JavaScript are your biggest enemies here.
✔ Bundling CSS into one file reduces the number of requests. (I use a bundler for this.)
✔ Defer non-essential JavaScript so it doesn’t block rendering.
Case Study: Real Shopify Store LCP Optimization
I tested a Shopify store using Lighthouse. Before optimizations:
⚠ LCP was ~12 seconds—brutal.
What I Optimized:
✅ Set fetchpriority="high" on the LCP image (ensuring it loads early).
✅ Lazy loaded all non-LCP images (to free up bandwidth).
✅ Preloaded fonts (so text didn’t wait for fonts to render).
✅ Bundled CSS using my bundler (reducing the number of requests).
💡 Results:
🚀 LCP improved from ~12s → ~4s
Next Steps for Further Optimization:
🔹 Split CSS into Critical & Non-Critical styles to further reduce render delay.
🔹 Monitor third-party Shopify apps—many inject unnecessary CSS/JS that delays rendering.
💡 Biggest remaining performance killers: Shopify apps adding extra CSS & JavaScript. Always audit your installed apps and check their impact on performance!
Conclusion & Next Steps
✔ LCP is affected by multiple factors, but Render Delay is usually the hardest to fix.
✔ The Performance Tab gives real data, while Lighthouse is a simulation—use both.
✔ Setting fetchpriority="high" is a simple but strong improvement—but doesn’t work with srcset.
✔ Lazy loading is great, but don’t use it on the LCP image.
✔ Shopify apps injecting render-blocking CSS/JS can kill performance—monitor them closely!
Next Steps:
👉 Check your Shopify store’s LCP in the Performance tab.
👉 Set fetchpriority="high" for your LCP image (if no srcset is used).
👉 Lazy load everything except your LCP image.
👉 Audit Shopify apps—see which ones slow you down.