Core Web Vitals: Why They Decide Your SEO Success in 2025
Since 2021, Core Web Vitals have been an official Google ranking factor. According to Google, 73% of users measure website quality by loading speed. A slow website costs you not just rankings, but customers β Amazon calculated that every 100ms delay means 1% revenue loss.
In this guide, we'll show you step by step how to measure, understand, and optimize your Core Web Vitals β with practical tips we've successfully implemented in dozens of client projects.
What Are Core Web Vitals? The Three Metrics Explained
Core Web Vitals are three specific metrics that measure your website's user experience:
1. Largest Contentful Paint (LCP) β Loading Time
What it measures: How long it takes until the largest visible content block is loaded (usually an image or text block).
Rating:
- Good: under 2.5 seconds
- Needs Improvement: 2.5 to 4.0 seconds
- Poor: over 4.0 seconds
Why it matters: LCP shows when users can see the main content. Slower LCP = higher bounce rate.
2. First Input Delay (FID) β Interaction to Next Paint (INP)
Important: Since March 2024, FID has been replaced by INP. INP is stricter and measures responsiveness across the entire session.
What it measures: How quickly the page responds to user interactions (clicks, taps, keystrokes).
Rating:
- Good: under 200 milliseconds
- Needs Improvement: 200 to 500 milliseconds
- Poor: over 500 milliseconds
3. Cumulative Layout Shift (CLS) β Visual Stability
What it measures: How much elements on the page shift during loading (e.g., when images or ads load in).
Rating:
- Good: under 0.1
- Needs Improvement: 0.1 to 0.25
- Poor: over 0.25
Why it matters: Layout shifts are extremely frustrating β e.g., when you want to click a button and suddenly an ad appears.
"Speed is a feature, not a luxury. Users expect sites to be fast, and slow sites lose customers." β Addy Osmani, Engineering Manager at Google Chrome
How to Measure Your Core Web Vitals
There are several tools to check your values:
1. Google PageSpeed Insights (free)
The most important tool. At pagespeed.web.dev enter your URL and receive Lab Data (simulated) and Field Data (real user data from Chrome UX Report).
Pro tip: Field data is more relevant for Google because it reflects real users. Lab data helps with debugging.
2. Google Search Console
Under "Core Web Vitals" in Search Console you can see which URLs have problems. Google categorizes your pages into: Good, Needs Improvement, Poor.
3. Lighthouse (in Chrome DevTools)
Open Chrome DevTools (F12), switch to "Lighthouse" and run an audit. Ideal for detailed technical analysis.
4. Web Vitals Chrome Extension
The Web Vitals Extension shows real-time values while browsing.
Optimizing LCP: The 7 Most Effective Measures
Largest Contentful Paint is often the biggest problem. Here's how to improve it:
1. Optimize Images
Images are usually the culprit. Our image optimization guide shows the details, here's the short version:
- Modern formats: WebP instead of JPEG/PNG (30-50% smaller)
- Right size: Don't serve images larger than needed
- Lazy loading: Load images outside viewport delayed
- Preload: Prioritize hero image with <link rel="preload">
2. Improve Server Response Time (TTFB)
Time To First Byte should be under 200ms:
- Choose better hosting (no shared hosting for business sites)
- Use CDN (Cloudflare, Fastly, AWS CloudFront)
- Enable caching (browser cache, server cache)
- Optimize database queries
3. Inline Critical CSS
CSS for the "above the fold" area should be directly in HTML, not in external files. Tools like Critical CSS Generator help with this.
4. Eliminate Render-Blocking Resources
JavaScript and CSS that block rendering delay LCP:
- Load JS with async or defer
- Delay non-critical CSS with media attributes
- Minimize third-party scripts (analytics, chat widgets, etc.)
5. Optimize Font Loading
Web fonts can significantly affect LCP:
- Use font-display: swap (show text immediately with fallback)
- Preload fonts with <link rel="preload" as="font">
- Only load required character sets (subsetting)
6. Clean Up Third-Party Scripts
Every external script costs performance: analytics, chatbots, social media widgets, retargeting pixels... Ask yourself: Do I really need this?
7. Use Modern Frameworks
At GoldenWing we use Next.js and React Server Components for optimal performance. This website has an LCP under 1.5 seconds.
Optimizing INP: Improving Responsiveness
Since March 2024, INP is the new standard. Here's how to optimize it:
1. Split JavaScript (Code Splitting)
Don't load all JS code at once. Dynamic imports and route-based splitting help.
2. Avoid Long Tasks
JavaScript tasks over 50ms block the main thread. Break up large calculations with requestIdleCallback or Web Workers.
3. Optimize Event Handlers
Event handlers should be fast. Offload heavy operations to requestAnimationFrame or setTimeout.
4. Isolate Third-Party Scripts
Load third-party scripts in iframes or with Web Workers to relieve the main thread.
Optimizing CLS: Preventing Layout Shifts
1. Always Specify Image Dimensions
Every <img> should have width and height attributes. Modern browsers then reserve space before the image loads.
2. Placeholders for Dynamic Content
For ads, embeds and dynamically loaded content: Reserve fixed areas with min-height.
3. Stabilize Fonts
With font-display: optional or swap and size-adjust you prevent font-related shifts.
4. Implement Animations Correctly
Use transform and opacity instead of width/height for animations. CSS containment (contain: layout) also helps.
Quick Wins: Measures You Can Implement Today
You can implement these optimizations today:
- WebP images: Convert all images to WebP
- Lazy loading: Add loading="lazy" to all images
- Preconnect: <link rel="preconnect"> for external domains
- Gzip/Brotli: Enable compression on server
- Browser caching: Set Cache-Control headers
Case Study: GoldenWing Website Optimization
When we migrated our own website to Next.js 15, we drastically improved Core Web Vitals:
Before (WordPress):
- LCP: 4.2 seconds
- INP: 380ms
- CLS: 0.18
After (Next.js 15):
- LCP: 1.4 seconds (-67%)
- INP: 95ms (-75%)
- CLS: 0.02 (-89%)
The result: Better Google rankings, lower bounce rate and faster page views. If you want similar results, talk to our SEO experts.
Core Web Vitals and SEO: The Direct Connection
Google has confirmed that Core Web Vitals are a ranking factor β but how strong?
The truth: Content quality and relevance are still more important. But between two similarly relevant pages, the faster one wins. Also: Good Core Web Vitals β better user experience β longer time on site β better rankings. A cycle.
Our advice: Don't obsess over perfect scores, but don't ignore them either. All three metrics in the "green zone" should be your goal.
Frequently Asked Questions
How often does Google update Core Web Vitals data?
Field Data in Chrome UX Report is updated monthly but is based on a 28-day rolling window. Changes need 4-6 weeks to show in the data.
My Lab data is good, but Field data is poor. Why?
Lab data is measured under ideal conditions. Field data comes from real users with slow devices, poor internet, or many tabs. Optimize for slower devices.
What Core Web Vitals values do I need for good rankings?
Google rates pages where at least 75% of users have good values as "passing". Aim for: LCP <2.5s, INP <200ms, CLS <0.1
Are Core Web Vitals different for Mobile and Desktop?
Yes, Google evaluates Mobile and Desktop separately. Mobile values are often worse due to slower processors and networks. Prioritize Mobile.
Do third-party widgets like chatbots affect Core Web Vitals?
Absolutely. Every third-party script can delay LCP, worsen INP and cause CLS. Load such widgets delayed and outside the critical path.
What's more important: LCP, INP or CLS?
For SEO, all three are relevant. For user experience, LCP is often most noticeable (slow loading annoys most). CLS is less frequent but extremely frustrating when it happens.
Can I improve Core Web Vitals with a page builder like Elementor?
Difficult. Page builders generate a lot of JavaScript and CSS. You can optimize (lazy loading, caching), but will never be as fast as a custom-developed solution. For performance-critical projects, we recommend professional web development.
Need help with Core Web Vitals optimization? Contact us for a free performance analysis of your website.
