Google: Lazy Loading Can Hurt Your LCP Score
▼ Summary
– Lazy loading above-the-fold images like hero images can delay Largest Contentful Paint (LCP) by making browsers treat them as low priority.
– Using the native loading=”lazy” attribute for images and iframes is preferred over JavaScript libraries as browsers handle it efficiently.
– Some lazy-loading libraries hide image URLs in custom attributes instead of standard src attributes, which can prevent Google from indexing those images.
– Core Web Vitals like LCP have a modest impact on search rankings, described as “a tiny minute factor in most cases.”
– Best practices include keeping above-the-fold images eager-loaded with dimensions set and using native lazy loading only for below-the-fold content.
A recent discussion on Google’s Search Off the Record podcast highlighted an important nuance in web performance optimization: lazy loading, while beneficial in many cases, can inadvertently harm your Largest Contentful Paint (LCP) score if misapplied. Martin Splitt and John Mueller explored real-world examples where well-intentioned defaults led to unintended delays in page rendering, particularly when critical above-the-fold content was affected.
Splitt pointed to developers.google.com as a cautionary example. The site’s content management system automatically applied lazy loading to every image, a common but risky practice. When hero images or other prominently placed visuals are lazy-loaded, the browser delays fetching them, treating them as lower priority. This directly impacts LCP, which measures how quickly the largest visible element appears on screen.
Under normal conditions, the browser’s preload scanner identifies important above-the-fold images early and prioritizes their download. Adding the loading=”lazy” attribute overrides this behavior, causing the browser to defer the request until after layout calculations and other resources have begun loading. The result is a delayed render of the most visually significant content, which pushes back the LCP timing. On slower networks or less powerful devices, this delay becomes even more pronounced. Missing width and height attributes can compound the issue, leading to unexpected layout shifts that degrade user experience.
Another concern involves older or custom lazy-loading scripts that rely on non-standard HTML attributes. While modern browsers support native lazy loading through the loading attribute, some third-party libraries store image URLs in custom data attributes like data-src instead of the standard src or srcset. If the actual image source isn’t present in the rendered HTML, search engines may not index those images properly. Splitt emphasized that Google’s systems look for URLs in standard source attributes, and anything outside of that may go unnoticed.
To avoid these pitfalls, web developers should adopt a more selective approach. Keep above-the-fold images eager-loaded by omitting the loading=”lazy” attribute for critical visuals like hero banners. Always include explicit width and height values to prevent layout instability. For content below the fold, native lazy loading remains a powerful and efficient tool. If using JavaScript-based lazy loading for dynamic content, ensure that the final rendered HTML includes image URLs in standard attributes.
It’s also wise to verify implementation using tools like Google Search Console’s URL Inspection tool. This allows you to review the fully rendered HTML and confirm that images are being handled correctly. While Core Web Vitals like LCP do influence rankings, their impact is generally modest compared to other SEO factors. Still, optimizing for a smooth user experience aligns with broader best practices for site performance and engagement.
Looking forward, the key is intentionality. Lazy loading should be treated as an opt-in feature for non-essential content, not a blanket solution. By carefully evaluating what content benefits from deferred loading and what requires immediate priority, developers can strike a balance that supports both performance and usability.
(Source: Search Engine Journal)
