What role does lazy loading play in Core Web Vitals?

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Anubhav Kumar · Answer

Lazy loading plays a huge role in optimizing Core Web Vitals, especially when it’s used strategically. It helps with performance, but like most tools, it needs to be used correctly.
Lazy Loading and Core Web Vitals — The Connection
and 
1. Largest Contentful Paint (LCP)
Lazy loading can help or hurt LCP depending on how it’s used:
Helps by deferring offscreen content (images/videos/scripts), allowing above-the-fold content to load faster.Hurts if you accidentally lazy-load the LCP image (e.g., hero image), delaying its load and worsening LCP.
Tip: Never lazy-load the image that contributes to LCP!
andlt;!-- GOOD: Eager load LCP image --andgt;
andlt;img src="hero.jpg" width="1200" height="600" loading="eager" /andgt;
and 
2. Cumulative Layout Shift (CLS)
Lazy loading images can cause layout shifts if you don’t reserve space for them.
Fix: Always set width and height attributes or use
aspect-ratio.
andlt;img src="card.jpg" loading="lazy" width="400" height="300" /andgt;
Or
img {
  aspect-ratio: 4 / 3;
}
and 
3. Interaction to Next Paint (INP) / First Input Delay (FID)
Lazy loading helps indirectly here:
By reducing the amount of JS/CSS/images loaded up front, it frees up the main thread.Less JS = faster interaction response times.
and 
Best Practices for Lazy Loading
Use loading="lazy" for below-the-fold images.Don’t lazy-load LCP images or key above-the-fold content.Preload fonts and LCP assets.Reserve space for lazy-loaded elements.Use JS lazy loaders for more control (especially for videos/iframes).
and 
Tools to Audit Lazy Loading
Chrome DevTools → Performance tab → Inspect image loading.Lighthouse → Look for warnings like "Avoid lazy-loading LCP image".PageSpeed Insights → Highlights lazy-load issues.

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What role does lazy loading play in Core Web Vitals?

Anubhav Kumar

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1 Answers

Lazy Loading & Core Web Vitals — The Connection

1. Largest Contentful Paint (LCP)

2. Cumulative Layout Shift (CLS)

3. Interaction to Next Paint (INP) / First Input Delay (FID)

Best Practices for Lazy Loading

Tools to Audit Lazy Loading

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