Core Web Vitals: What They Are & Why They Matter for SEO in 2025

What is Core Web Vitals ?

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. They are part of Google’s page experience signals and impact search rankings. These metrics focus on three key aspects of web performance:

Largest Contentful Paint (LCP) – Measures loading performance. It tracks how long it takes for the largest visible content element (like an image or text block) to appear on the screen.

• Ideal LCP: Under 2.5 seconds

First Input Delay (FID) / Interaction to Next Paint (INP) – Measures interactivity. It tracks the time between a user’s first interaction (like clicking a button) and the browser’s response.

• Ideal FID: Under 100 milliseconds

• Note: Google is replacing FID with INP (Interaction to Next Paint) in March 2024. INP measures responsiveness more comprehensively.

Cumulative Layout Shift (CLS) – Measures visual stability. It tracks how much elements shift unexpectedly while the page loads.

• Ideal CLS: Less than 0.1

Why Are Core Web Vitals Important?

• They impact SEO rankings since Google prioritizes sites with a good user experience.

• Improving them enhances user engagement, conversions, and overall satisfaction.

• They help diagnose and fix performance issues on websites.

You can check Core Web Vitals using tools like Google PageSpeed Insights, Lighthouse, Search Console, and Chrome DevTools.

Also Read: Top SEO Trends for Advanced Technology Websites

First Contentful Paint (FCP)

First Contentful Paint (FCP) is a performance metric that measures the time it takes for the first piece of content (like text, images, or SVGs) to appear on the screen after a user navigates to a webpage. It indicates when users first see something meaningful, even if the page isn’t fully loaded yet.

How is FCP Measured?

• FCP is recorded in milliseconds (ms) or seconds (s) from when the browser starts loading the page to when the first visible element appears.

• It’s considered good if it happens within 1.8 seconds.

FCP Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 1.8s

• ⚠️ Needs Improvement: 1.8s – 3.0s

• ❌ Poor: Above 3.0s

How to Improve FCP?

1. Optimize Server Response Time – Use a fast hosting service and a CDN.

2. Minimize Render-Blocking Resources – Defer non-critical JavaScript & CSS.

3. Optimize CSS and Fonts – Use preloading for key resources.

4. Use Efficient Image Formats – WebP and AVIF load faster than PNG/JPEG.

5. Enable Browser Caching – Reduce reloading time for returning users.

Why is FCP Important?

A faster First Contentful Paint improves user experience by making the page feel responsive and engaging. If FCP is slow, users may leave before the page fully loads, increasing bounce rates.

Largest Contentful Paint (LCP)

Largest Contentful Paint (LCP) is a Core Web Vital metric that measures how long it takes for the largest visible content element (such as an image, video, or text block) to load and render on the screen. It reflects the perceived loading speed of a webpage.

How is LCP Measured?

• LCP is recorded in seconds from when the page starts loading to when the largest content element becomes visible.

• Google considers LCP good if it occurs within 2.5 seconds.

LCP Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 2.5s

• ⚠️ Needs Improvement: 2.5s – 4.0s

• ❌ Poor: Above 4.0s

What Elements Can Be Considered for LCP?

• <img> images

• <video> thumbnails

• <div> or <p> blocks with background images

• <h1>, <h2>, or other large text elements

How to Improve LCP?

1. Optimize Server Response Time – Use fast hosting and a CDN to speed up content delivery.

2. Enable Caching – Store frequently used resources to reduce load times.

3. Optimize Images & Videos – Use next-gen formats (WebP, AVIF) and compress images.

4. Minimize Render-Blocking Resources – Defer non-essential JavaScript and CSS.

5. Use Lazy Loading – Load images only when needed to speed up initial page load.

6. Preload Important Resources – Use <link rel=”preload”> for key assets like fonts and hero images.

Why is LCP Important?

A slow LCP can frustrate users and increase bounce rates, while a fast LCP improves user experience, engagement, and SEO rankings.

Also Read: How to Improve Search Rankings: Complete SEO Strategy Guide 2024

Total Blocking Time (TBT)

Total Blocking Time (TBT) is a web performance metric that measures the total amount of time during which a webpage is unresponsive to user interactions while loading. It helps determine how smoothly a page loads and responds to user input.

How is TBT Measured?

• TBT measures the time (in milliseconds) between First Contentful Paint (FCP) and Time to Interactive (TTI) when the main thread is blocked for more than 50 milliseconds.

• When the browser’s main thread is busy executing long tasks (JavaScript execution, parsing, or rendering), it can’t respond to user inputs like clicks or scrolling.

TBT Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 200 ms

• ⚠️ Needs Improvement: 200 – 600 ms

• ❌ Poor: Above 600 ms

How to Improve TBT?

1. Minimize Long JavaScript Tasks – Break large tasks into smaller chunks (less than 50ms each).

2. Defer or Remove Unused JavaScript – Use async or defer attributes for scripts that are not critical.

3. Optimize Third-Party Scripts – Reduce the number of third-party widgets and analytics scripts.

4. Use Web Workers – Move heavy computations off the main thread to keep it responsive.

5. Reduce Render-Blocking Resources – Minimize CSS and JavaScript that delay rendering.

6. Optimize and Compress Code – Minify JavaScript, CSS, and HTML files.

7. Lazy Load Non-Essential Elements – Load only necessary elements first to improve responsiveness.

Why is TBT Important?

A high TBT means that users experience delays when interacting with a webpage, leading to frustration and a poor user experience. Lowering TBT can significantly improve site responsiveness and SEO rankings.

Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) is a Core Web Vital metric that measures the visual stability of a webpage. It calculates how much elements unexpectedly shift during the page load, which can be frustrating for users.

How CLS is Measured?

CLS is a score (not a time-based metric) that represents how much visible content moves unexpectedly. The score is calculated based on:

1. Impact Fraction – How much the unstable element affects the viewport.

2. Distance Fraction – How far the element moves relative to the viewport size.

Example of CLS in Action:

• A button shifts while a user is about to click, causing them to click something else.

• Text moves because an image or ad loads late, pushing content down.

CLS Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 0.1

• ⚠️ Needs Improvement: 0.1 – 0.25

• ❌ Poor: Above 0.25

Common Causes of High CLS

1. Images & Ads Without Dimensions – Not setting width & height causes layout shifts.

2. Dynamically Injected Content – Loading banners, ads, or embeds late can push content down.

3. Slow Font Loading (FOUT/FOIT) – Flash of Unstyled/Invisible Text can change layouts.

4. Animations & Transitions – Uncontrolled animations can shift elements.

How to Improve CLS?

1. Define Image & Video Dimensions – Always set width and height for media elements.

2. Reserve Space for Ads & Embeds – Use CSS containers with a fixed height to prevent shifting.

3. Use Font Display Strategies – Use font-display: swap; to prevent sudden text changes.

4. Avoid Unexpected Content Injection – Load UI elements in a predictable way.

5. Use Transform Instead of Changing Layout – CSS animations should use transform instead of affecting the document flow.

Why is CLS Important?

A high CLS makes a website feel unstable, leading to a frustrating user experience and higher bounce rates. Google prioritizes pages with a low CLS in search rankings.

Also Read: Microformat Markup: What They Are, How to Use Them, and SEO Benefits

Speed Index (SI)

Speed Index (SI) is a web performance metric that measures how quickly the visible content of a webpage is displayed during loading. It represents the perceived loading experience for users.

How Speed Index is Measured?

Speed Index is calculated using a video capture of the page load process and measures how long it takes for above-the-fold content (content visible without scrolling) to become fully rendered. The lower the Speed Index, the better the user experience.

Speed Index Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 3.4s

• ⚠️ Needs Improvement: 3.4s – 5.8s

• ❌ Poor: Above 5.8s

Factors Affecting Speed Index

1. Slow Server Response – A slow backend delays page rendering.

2. Render-Blocking Resources – CSS and JavaScript files that delay content display.

3. Large Images & Videos – Heavy media takes longer to load and display.

4. JavaScript Execution Time – Unoptimized scripts slow down rendering.

5. Third-Party Scripts – Ads, analytics, and social media widgets can increase SI.

How to Improve Speed Index?

1. Optimize Critical Rendering Path – Prioritize loading key elements first.

2. Minify CSS & JavaScript – Reduce file sizes and remove unused code.

3. Use Lazy Loading – Load images/videos only when needed.

4. Enable Browser Caching – Store static resources locally to reduce reload times.

5. Use a Content Delivery Network (CDN) – Distribute content from servers closer to users.

6. Reduce Third-Party Scripts – Limit external scripts like ads and tracking codes.

7. Preload Important Resources – Use <link rel=”preload”> for fonts, images, and CSS.

Why is Speed Index Important?

A lower Speed Index means a page visually loads faster, improving user engagement and SEO rankings. Since Google considers page experience in search rankings, optimizing SI can boost your site’s visibility.

Interaction to Next Paint (INP)

Interaction to Next Paint (INP) is a web performance metric that measures a webpage’s responsiveness. It evaluates how long it takes for the browser to visually update the page after a user interaction, such as clicking a button, tapping a link, or typing in a form.

Why Is INP Important?

• A slow INP means users experience delays when interacting with a webpage, leading to frustration.

• Google is replacing First Input Delay (FID) with INP in March 2024 as a Core Web Vital because INP measures responsiveness more comprehensively.

How INP Works

• INP records the worst-case interaction latency rather than just the first interaction (unlike FID).

• It measures the delay, processing time, and rendering time of an interaction.

• A single high INP value (such as a slow button click) can negatively impact a website’s perceived performance.

INP Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 200 ms

• ⚠️ Needs Improvement: 200 – 500 ms

• ❌ Poor: Above 500 ms

Common Causes of High INP

1. Heavy JavaScript Execution – Slow JavaScript blocks the main thread.

2. Render-Blocking Resources – Large CSS/JavaScript files delay updates.

3. Large DOM Size – Too many elements slow down interactions.

4. Third-Party Scripts – Ads, trackers, and social media widgets can delay UI updates.

5. Expensive Event Handlers – Poorly optimized event listeners cause delays.

How to Improve INP?

1. Minimize JavaScript Execution – Optimize and split long tasks into smaller chunks.

2. Reduce Render-Blocking Resources – Defer or async non-essential scripts.

3. Optimize Event Handlers – Use efficient, non-blocking event listeners.

4. Use Web Workers – Offload heavy computations from the main thread.

5. Reduce DOM Size & Complexity – Simplify layouts and remove unnecessary elements.

6. Optimize Third-Party Scripts – Remove unnecessary widgets or load them asynchronously.

7. Prioritize User Actions – Load interactive elements quickly and defer non-essential scripts.

Why Should You Optimize INP?

A low INP ensures a smooth, responsive user experience, leading to better engagement and SEO rankings. Since Google is making INP a Core Web Vital, improving it will directly impact your website’s search performance.

Also Read: Product Page SEO : Guide to Driving Traffic and Boosting Conversions

Time to First Byte (TTFB)

Time to First Byte (TTFB) is a performance metric that measures the time taken for a user’s browser to receive the first byte of data from the server after making an HTTP request. It reflects the speed of the server’s response.

How TTFB is Measured?

TTFB is the sum of three key processes:

1. Request Sending Time – The time it takes for the browser to send a request to the server.

2. Server Processing Time – How long the server takes to generate a response.

3. Response Delay – The time taken for the first byte of data to travel back to the browser.

TTFB Score Ranges (Google’s Benchmarks):

• ✅ Good: 0 – 800 ms

• ⚠️ Needs Improvement: 800 – 1,800 ms

• ❌ Poor: Above 1,800 ms

Common Causes of High TTFB

1. Slow Server Response – Poor hosting or overloaded servers.

2. Unoptimized Database Queries – Slow queries delay response generation.

3. High Traffic Without Caching – Each request forces the server to regenerate content.

4. Large Redirect Chains – Too many redirects slow down the response.

5. No CDN Usage – Users far from the origin server experience higher latency.

6. Heavy Dynamic Content – Complex backend processing slows down responses.

How to Improve TTFB?

1. Use a Fast & Reliable Hosting Provider – Upgrade to a high-performance server.

2. Enable Caching – Use server-side caching (e.g., Redis, Memcached) and CDNs to serve cached responses faster.

3. Optimize Database Queries – Index tables and optimize queries to reduce processing time.

4. Minimize Redirects – Reduce unnecessary redirections to speed up the first response.

5. Use a Content Delivery Network (CDN) – Serve content from geographically closer servers.

6. Optimize Web Server Configurations – Tune Apache, Nginx, or LiteSpeed settings for better efficiency.

7. Reduce Backend Processing Time – Use optimized PHP, Node.js, Python scripts and minimize expensive computations.

Why is TTFB Important?

• Fast TTFB = Faster Page Load Times, improving user experience.

• A lower TTFB boosts SEO rankings, as Google considers page speed in search rankings.

• It helps reduce bounce rates, as users are more likely to stay on a site that loads quickly.

Why Are Core Web Vitals Important?

Core Web Vitals (CWV) are crucial because they directly impact user experience (UX), search rankings (SEO), and conversion rates. These metrics—LCP (Largest Contentful Paint), INP (Interaction to Next Paint), and CLS (Cumulative Layout Shift)—help measure a website’s loading speed, responsiveness, and visual stability.

1️⃣ Impact on User Experience

A fast, smooth website keeps users engaged. Slow load times or layout shifts frustrate visitors, leading to higher bounce rates.

• Fast LCP → Users see content quickly

• Low INP → Page responds instantly to interactions

• Low CLS → Prevents annoying layout shifts

2️⃣ SEO & Google Rankings

• Google uses Core Web Vitals as a ranking factor in search results.

• Websites with good CWV scores get higher visibility in Google Search.

• Poor scores can lower rankings, reducing organic traffic.

3️⃣ Better Conversion Rates & Revenue

• Faster, responsive websites improve engagement and sales.

• Studies show that 1-second delay can reduce conversions by up to 20%.

• A smooth UX increases trust and satisfaction, leading to more repeat visitors.

4️⃣ Mobile Optimization

• Core Web Vitals are even more critical for mobile users, where slow loading and unresponsive interactions are more noticeable.

• Google prioritizes mobile-friendly sites with good CWV scores in its Mobile-First Indexing.

5️⃣ Competitive Advantage

• If your site loads faster and feels smoother than competitors, users are more likely to stay and convert.

• Improving CWV gives an edge in search rankings and customer retention.

Also Read: Answer Engine Optimization (AEO): Beyond Traditional SEO

Conclusion

✅ Better UX → Happy visitors ✅ Higher SEO rankings → More traffic ✅ Improved conversions → More revenue

Would you like help in optimizing your website’s Core Web Vitals?