Why Google Says Lazy Loading Can Delay LCP

Google has shed light on how lazy loading can affect a website’s performance, particularly when it comes to one of the most important user experience metrics: the Largest Contentful Paint (LCP). In a recent podcast, Martin Splitt from Google explained why default lazy loading may create issues and what website owners should keep in mind when implementing it.

Lazy loading is a common technique used by developers to improve page speed. Instead of loading all images at once, it only loads them when a visitor scrolls near them. While this can save bandwidth and speed up initial page load, Splitt highlighted that when it comes to images above the fold—those that users see straight away—it can actually do more harm than good.

The key issue is that lazy loading can delay the Largest Contentful Paint, which measures how quickly the main content of a page becomes visible to users. Since LCP is one of Google’s Core Web Vitals and an important ranking factor, a delay here can negatively impact both user experience and search performance.

Google’s advice is clear: avoid lazy loading for above-the-fold images. When these images don’t appear immediately, users may experience a jarring delay, giving the impression that the page is slow to respond—even if the rest of the site loads quickly. This can lead to higher bounce rates and weaker engagement.

Another concern raised by Splitt is the use of certain libraries that claim to optimise lazy loading. While they may help in some cases, others can interfere with how Googlebot indexes pages. This means that search engines might not properly recognise or display key content, potentially harming a site’s visibility in search results.

To prevent these problems, Splitt recommends that developers test their implementations carefully. One of the most effective ways to do this is by checking the rendered HTML in Google Search Console. By doing so, site owners can see exactly how Google is interpreting their pages and identify whether important images or elements are being missed.

This guidance underscores the balance developers must strike between technical optimisation and user experience. While lazy loading is a valuable tool, applying it without consideration for above-the-fold content can create unintended setbacks. The goal should always be to deliver speed improvements without disrupting the way users perceive and interact with the site.

For businesses that rely heavily on visuals, such as ecommerce websites, this advice is particularly relevant. Product images placed at the top of a page are crucial for attracting attention and encouraging engagement. If those images are delayed by lazy loading, the impact on conversions could be significant.

Splitt’s comments also serve as a reminder that SEO is not just about search engine rankings but also about overall usability. Google continues to place strong emphasis on Core Web Vitals, reinforcing the message that user-centred design and technical best practices go hand in hand.

In summary, lazy loading remains a useful performance technique, but it must be applied wisely. Avoiding it for above-the-fold images, testing in Search Console, and choosing libraries carefully can help website owners strike the right balance between speed, accessibility, and user satisfaction.

How Lazy Loading Delays LCP

The Largest Contentful Paint (LCP) measures when the biggest text block or image within the initial screen area is displayed to the user.

In most cases, the browser’s preload scanner quickly detects the main “hero” image and fetches it with high priority so that it appears on the page as soon as possible.

However, when the attribute loading=”lazy” is applied to that same hero image, the way the browser handles it changes.

Instead of treating the image as a top priority, the browser lowers its importance, allowing other files and resources to load ahead of it.

This means the browser holds off on fetching the image until it has already carried out some layout work and other processing

SEO Risk With Some Libraries

Modern browsers now come with a built-in loading attribute for both images and iframes, which removes the need to rely on bulky JavaScript for most common use cases. WordPress has made native lazy loading the default option, which has contributed to its widespread adoption.

According to Martin Splitt, this feature allows the browser itself to manage lazy loading automatically, taking the burden off developers.

However, older or customised lazy-loading libraries often store image URLs in unusual attributes instead of the standard ones. This can cause problems because if the actual image link does not appear in src or srcset within the HTML that Google processes, those images might not be recognised or indexed properly.

Splitt pointed out that Google has come across several lazy-loading libraries using attributes like data-source instead of the standard src. When this happens, Google’s systems are unable to detect the images, as they only read the recognised attributes.

How To Check Your Pages

Google recommends using the URL Inspection tool in Search Console to check the rendered HTML of a page. This helps ensure that key images appearing above the fold, as well as lazy-loaded elements, are using proper standard attributes. It’s best not to rely solely on the screenshot feature, as it doesn’t always give the full picture.

Martin Splitt explained that if the rendered HTML clearly shows the image URLs within the src attribute of the image tag, then everything should work as expected and there’s nothing to worry about.

When it comes to search rankings, Splitt suggested that the impact of lazy loading is relatively minor. Core Web Vitals, including Largest Contentful Paint (LCP), do play a role in ranking, but the effect is generally quite small in most cases.

For practical steps, Splitt advised keeping hero images and other above-the-fold visuals set to load eagerly, and making sure they include width and height attributes to prevent layout shifts.

For content that sits below the fold, it’s more efficient to use the native loading=”lazy” attribute for both images and iframes. This ensures faster loading of critical content without overburdening the page.

If you’re depending on a lazy-loading library for videos, previews, or dynamic sections, it’s important to double-check that the final HTML outputs proper URLs in standard attributes. Without this, Google may struggle to pick them up during indexing.

The best way to verify this is by reviewing the rendered HTML in Search Console rather than relying on static previews. This helps confirm that Google can access and understand all the necessary resources.

Looking at the bigger picture, lazy loading should be used with care. It works best when applied to non-essential elements, rather than being rolled out across everything by default.

By treating lazy loading as an option for less critical content, websites can balance performance improvements without harming visibility or user experience.

Finally, keeping an eye on your site’s LCP performance over time will give you a clear indication of whether your implementation is working properly, and if any adjustments are needed to maintain a smooth experience for users.