Why Lazy Loading Can Delay Largest Contentful Paint (LCP)

Lazy loading is a popular web development technique that delays the loading of images and resources until they are actually needed – usually when the user scrolls down. While this can save bandwidth and improve performance, it can also delay Largest Contentful Paint (LCP) if used incorrectly.

LCP is one of the Core Web Vitals and a key factor for both SEO and user experience, so it’s important to understand how lazy loading impacts it.

What is LCP?

Largest Contentful Paint (LCP) measures the time it takes for the largest visible image or text block to render on screen.

• ✅ Good: under 2.5 seconds
• ⚠️ Needs Improvement: 2.5–4 seconds
• ❌ Poor: above 4 seconds

A faster LCP means users can see the most important part of your page sooner, creating a smoother experience.

How Lazy Loading Affects LCP

Lazy loading becomes problematic when above-the-fold images (such as hero images or large banners) are lazy-loaded. In that case, the browser:

• Assigns lower priority to the image
• Waits for other resources (scripts, styles) before loading it
• Splits bandwidth with other assets

👉 This means the most important element – the one users see first – appears too late, delaying LCP.

Example: A homepage hero image with loading="lazy" may show as a blank box for several seconds before it renders.

SEO Risks with Lazy Loading Libraries

Not all lazy loading libraries are SEO-friendly. Some older ones hide image URLs inside custom attributes like data-src instead of standard HTML (<img src="">). This can cause:

• Search engines failing to index images
• Images missing from Google Image Search
• Pages appearing content-thin to crawlers

Tip: Prefer the built-in HTML attribute loading="lazy" or use libraries that ensure the actual src attribute is available in the rendered HTML.

How to Check Your Pages

You can easily verify if your implementation is safe:

1. Google Search Console → URL Inspection
   • Check if important images appear correctly in the rendered HTML.
2. Lighthouse (Chrome DevTools)
   • Test your LCP score and see which resource delays it.
3. WebPageTest.org
   • Visualize exactly when each resource loads.

👉 Pay extra attention to hero images and largest above-the-fold content.

Actionable Tips to Improve LCP

Here’s a practical checklist:

1. Prioritize Hero Images

Use `loading=”eager”` for above-the-fold images and set `fetchpriority=”high”`.

<img src="hero.jpg" width="1200" height="600" loading="eager" fetchpriority="high" alt="Hero image">

2. Preload Critical Images

For your most important image, preload it:

<link rel="preload" as="image" href="hero.jpg">

3. Define Dimensions

Always set width and height attributes to prevent layout shifts and allow browsers to allocate space.

4. Use Lazy Loading Strategically

– ✅ Yes: images far down the page, galleries, blog lists

– ❌ No: hero images, banners, logos, featured product images

5. Optimize Image Format & Size

– Use WebP or AVIF formats
– Compress images without visible quality loss
– Provide responsive images via srcset

6. Monitor LCP Regularly

– Test with PageSpeed Insights
– Track real-world data with Chrome UX Report
– Set up Web Vitals tracking in Google Analytics

Why It Matters: SEO & Conversions

LCP is not just a ranking factor – it also affects engagement and sales:

• ✅ Fast LCP → better first impression → higher conversions
• ❌ Slow LCP → frustrated users → higher bounce rate

Improving LCP is often one of the fastest ways to increase both organic visibility and user satisfaction.

Conclusion

Lazy loading is powerful, but it must be used wisely:

• Lazy load non-critical content (images further down the page)
• Eager load above-the-fold content (hero, banners, key visuals)
• Measure, test, and adjust regularly

Balancing lazy loading with LCP optimization ensures faster pages, happier users, and better SEO results.

Quick Checklist

• ✅ Don’t lazy load hero/above-the-fold images
• ✅ Use loading="eager" + fetchpriority="high" for critical images
• ✅ Preload your main hero image
• ✅ Always define width and height
• ✅ Use WebP/AVIF for smaller, faster images
• ✅ Monitor LCP with Lighthouse & GSC