Core Web Vitals & Performance

Make your site fast enough to rank and convert visitors

Reality Check: Performance is a lightweight ranking factor. Focus on content quality first, then optimize performance to avoid penalties and improve user experience. You don't need a perfect 100 score to rank well.

What Are Core Web Vitals?

Google's key metrics for measuring user experience on the web

Core Web Vitals (CWV) are a set of metrics introduced by Google in 2021 as part of the Page Experience update. They measure real-world user experience focused on loading speed, visual stability, and interactivity.

Why They Matter for SEO

• Confirmed ranking factor since 2021
• Affects mobile and desktop rankings
• Poor scores can prevent top rankings
• Influences user engagement & conversions

Important Context

• Lightweight factor: Content quality matters more
• Threshold-based: Pass/fail, not linear scoring
• Based on real user data (28-day rolling)
• Mobile scores matter most

CWV is a LIGHTWEIGHT ranking factor - content quality, relevance, and backlinks still dominate. Think of CWV as a tie-breaker: if two pages are equally relevant, the faster one wins.

The Three Core Metrics

Learn what each metric measures and how to interpret the scores

LCP - Largest Contentful Paint

Loading Performance

Definition: Time until the largest visible element (image, video, or text block) loads

Good

< 2.5 seconds

Needs Work

2.5 - 4.0 seconds

Poor

> 4.0 seconds

Common Causes:

• Large unoptimized images (biggest culprit)
• Slow server response time (TTFB)
• Render-blocking CSS/JavaScript
• Client-side rendering delays

User Impact: "When can I see the main content?" - LCP directly affects perceived load time and whether users wait or bounce.

CLS - Cumulative Layout Shift

Visual Stability

Definition: How much content jumps around while loading (measured as a score, not time)

Good

< 0.1

Needs Work

0.1 - 0.25

Poor

> 0.25

Common Causes:

• Images without width/height attributes
• Ads, embeds, iframes without reserved space
• Web fonts causing FOIT/FOUT (flash of invisible/unstyled text)
• Dynamic content injected above existing content

User Impact: "Did I accidentally click the wrong thing?" - Layout shifts cause misclicks and frustration, especially on mobile.

INP - Interaction to Next Paint

Responsiveness (replaced FID in March 2024)

Definition: How fast the page responds to user interactions (clicks, taps, keyboard)

Good

< 200 milliseconds

Needs Work

200 - 500 milliseconds

Poor

> 500 milliseconds

Common Causes:

• Heavy JavaScript execution blocking main thread
• Long tasks (>50ms) preventing responsiveness
• Large DOM size (1000+ nodes)
• Third-party scripts running on interaction

User Impact: "Why isn't the page responding?" - Poor INP makes sites feel sluggish and unresponsive, especially on lower-end devices.

Other Important Metrics

Secondary metrics that provide additional insights

TTFB - Time to First Byte

Server response speed. Affects LCP. Good < 800ms.

FCP - First Contentful Paint

When first content appears. Good < 1.8s.

Speed Index

How quickly content is visually displayed. Good < 3.4s.

Total Blocking Time

How long page is unresponsive. Good < 200ms.

Mobile vs Desktop: Why Mobile Matters Most

Mobile Performance

• Google primarily uses mobile scores for ranking
• Typically 2-3x worse than desktop
• Tested on 4G connection (not 5G or WiFi)
• Lower-powered devices (mid-range phones)

Desktop Performance

• Usually easier to optimize
• Less impact on SEO rankings
• Still matters for user experience
• Don't ignore it, just prioritize mobile

Priority: Focus on mobile first - it's what Google judges you on. Once mobile scores are good (70+), then optimize desktop if needed.