How to Add Lazy Load Images in Blogger

 20 images loading at once = 5s LCP fail. Lazy load = only load images when user scrolls.

In this tutorial, you'll add lazy loading to all Blogger images. Follow along and you'll pass Core Web Vitals LCP + rank higher in 2025.

Step 1: Why Lazy Load Images is Critical for Blogger 2025

Google made lazy load a ranking factor. No lazy load = traffic drop.

1. Core Web Vitals: Lazy load fixes LCP. Pass under 2.5s easily
2. Bandwidth: Users save 60% data. Mobile users stay longer
3. AdSense: Faster page = more ads load before user bounces
4. SEO: Google prioritizes fast sites since 2021 Page Experience update

Image: PageSpeed showing LCP improvement after lazy load

Step 2: Auto Lazy Load All Images in Blogger Theme

This code adds loading="lazy" to every image automatically. 1-minute setup.

1. Blogger → Theme → Edit HTML → Ctrl+F → Search </body>
2. Paste this code ABOVE </body>:

<script>
//<![CDATA[
document.addEventListener("DOMContentLoaded", function() {
  var images = document.querySelectorAll("img");
  for (var i = 0; i < images.length; i++) {
    // Skip first image for LCP
    if (i === 0) continue;
    // Skip images above the fold
    if (images[i].getBoundingClientRect().top < window.innerHeight) continue;
    images[i].setAttribute("loading", "lazy");
  }
});
//]]>
</script>

3. Save theme → All images below fold now lazy load

Step 3: Manual Lazy Load for Single Image

Want control? Add lazy load to specific images in post editor.

1. Upload image in post → Switch to "HTML" view
2. Find your img tag → Add loading="lazy":

<img src="image.jpg" alt="description" width="800" height="600" loading="lazy">

3. Important: Always add width and height to prevent CLS layout shift

Step 4: Lazy Load Background Images + iframes

YouTube embeds and background images kill speed. Lazy load them too.

For YouTube iframes:

<iframe loading="lazy" width="560" height="315" 
src="https://www.youtube.com/embed/VIDEO_ID" 
title="YouTube video" frameborder="0" allowfullscreen></iframe>

For CSS background images:

<style>
.lazy-bg {
  background-image: none!important;
}
.lazy-bg.loaded {
  background-image: url('image.jpg');
}
</style>

<div class="lazy-bg" data-bg="image.jpg"></div>

<script>
document.addEventListener("DOMContentLoaded", function() {
  var lazyBg = document.querySelectorAll('.lazy-bg');
  var observer = new IntersectionObserver(function(entries) {
    entries.forEach(function(entry) {
      if (entry.isIntersecting) {
        entry.target.style.backgroundImage = 'url(' + entry.target.dataset.bg + ')';
        entry.target.classList.add('loaded');
        observer.unobserve(entry.target);
      }
    });
  });
  lazyBg.forEach(function(bg) { observer.observe(bg); });
});
</script>

Step 5: Test Lazy Load + Core Web Vitals 2025

Test	How to Check	Pass Result
LCP score	pagespeed.web.dev → Test post URL	Under 2.5s, Green
Images loading	Chrome DevTools → Network → Img → Scroll page	Images load only when visible
CLS score	PageSpeed → Must stay under 0.1	No layout shift from images
First image	Check HTML → First img must NOT have loading="lazy"	LCP image loads immediately

1. Fix: Images not showing = JS disabled. Add <noscript><img src="image.jpg"></noscript> fallback
2. Fix: CLS jump = Missing width/height. Always add dimensions to img tag

Bad practice to avoid: Lazy loading first image or logo. Kills LCP score. Only lazy load images below the fold.

Important: Blogger added native lazy load in 2020 but it's buggy. This JS method is 100% reliable. Test after adding new images. Combine with WebP format from Post #43 speed guide for max results. Lazy load doesn't work in RSS feeds - that's normal.