Since 2021, Core Web Vitals have been official Google ranking factors. In 2025, they're more important than ever. Here's everything you need to know.
What Are Core Web Vitals?
Core Web Vitals measure real-world user experience through three metrics:
1. Largest Contentful Paint (LCP)
What it measures: Loading performance—how long until the main content is visible
- Good: ≤2.5 seconds
- Needs Improvement: 2.5-4 seconds
- Poor: >4 seconds
2. Interaction to Next Paint (INP)
What it measures: Responsiveness—how quickly the page responds to user interactions
- Good: ≤200 milliseconds
- Needs Improvement: 200-500 milliseconds
- Poor: >500 milliseconds
Note: INP replaced First Input Delay (FID) in March 2024
3. Cumulative Layout Shift (CLS)
What it measures: Visual stability—how much the page layout shifts unexpectedly
- Good: ≤0.1
- Needs Improvement: 0.1-0.25
- Poor: >0.25
How They Affect Rankings
Core Web Vitals are part of Google's "page experience" signals:
- They act as a tiebreaker between similarly relevant content
- Pages with good scores may get a ranking boost
- Poor scores won't necessarily tank rankings, but help competitors
- Mobile and desktop are evaluated separately
Improving LCP
Common Causes of Poor LCP
- Slow server response time
- Render-blocking JavaScript and CSS
- Large, unoptimized images
- Client-side rendering delays
How to Fix
- Optimize images: Use WebP, proper sizing, lazy loading
- Use a CDN: Serve assets from edge locations
- Preload critical resources: Tell browser what to fetch first
- Server-side rendering: Send HTML instead of empty shell
- Reduce server response time: Optimize backend, use caching
Improving INP
Common Causes of Poor INP
- Heavy JavaScript execution
- Large JavaScript bundles
- Long tasks blocking the main thread
- Third-party scripts
How to Fix
- Code splitting: Load only what's needed
- Defer non-critical JS: Use async/defer attributes
- Break up long tasks: Use requestIdleCallback, web workers
- Audit third-party scripts: Remove or defer non-essential ones
- Optimize event handlers: Debounce, use passive listeners
Improving CLS
Common Causes of Poor CLS
- Images without dimensions
- Ads, embeds, iframes without reserved space
- Dynamically injected content
- Web fonts causing FOUT/FOIT
How to Fix
- Always include size attributes: width/height on images and videos
- Reserve space for ads: Use min-height containers
- Avoid inserting content above existing content
- Preload fonts: Use font-display: swap
- Use transform animations: Instead of properties that trigger layout
Tools for Measurement
Lab Data (Simulated)
- Lighthouse: Built into Chrome DevTools
- PageSpeed Insights: Google's testing tool
- WebPageTest: Detailed waterfall analysis
Field Data (Real Users)
- Chrome UX Report (CrUX): Real user data from Chrome
- Search Console: Core Web Vitals report
- Web Vitals JavaScript library: Measure in your own analytics
Next.js Advantage
This is why we use Next.js—it handles many optimizations automatically:
- Automatic image optimization
- Built-in font optimization
- Automatic code splitting
- Server-side rendering
- Static generation
Need help improving your Core Web Vitals? We audit sites and implement fixes. Let's discuss.