---
title: "What role does lazy loading play in Core Web Vitals?"  
description: "What role does lazy loading play in Core Web Vitals?"  
author: "Anubhav Sharma"  
published: 2025-04-06  
updated: 2025-04-06  
canonical: https://www.mindstick.com/interview/34029/what-role-does-lazy-loading-play-in-core-web-vitals  
category: "web development"  
tags: ["web development"]  
reading_time: 3 minutes  

---

# What role does lazy loading play in Core Web Vitals?

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 & Core Web Vitals — The Connection

#### 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!

```html
<!-- GOOD: Eager load LCP image -->
<img src="hero.jpg" width="1200" height="600" loading="eager" />
```

#### 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`.

```html
<img src="card.jpg" loading="lazy" width="400" height="300" />
```

Or

```css
img {
  aspect-ratio: 4 / 3;
}
```

#### 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.

#### 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).

#### 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.

## Answers

### Answer by Anubhav Sharma

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 & Core Web Vitals — The Connection

#### 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!

```html
<!-- GOOD: Eager load LCP image -->
<img src="hero.jpg" width="1200" height="600" loading="eager" />
```

#### 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`.

```html
<img src="card.jpg" loading="lazy" width="400" height="300" />
```

Or

```css
img {
  aspect-ratio: 4 / 3;
}
```

#### 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.

#### 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).

#### 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.


---

Original Source: https://www.mindstick.com/interview/34029/what-role-does-lazy-loading-play-in-core-web-vitals

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