Load time costs visitors: A widely cited Google study (DoubleClick, "The Need for Mobile Speed", 2016) found that 53% of mobile site visits are abandoned if loading takes longer than 3 seconds. The figure isn't fresh anymore, and your own analytics data will tell you more. Core Web Vitals have been an official ranking factor in Google Search since 2021. On Google Ads their effect is only indirect: Google names faster loading as a way to improve landing page experience, which is one of the three components of your Google Ads Quality Score.
What Are Core Web Vitals?
Core Web Vitals are three measurable metrics Google uses to assess your website's user experience:
LCP: Largest Contentful Paint
What: How long does it take for the largest visible element (image, video, text block) to load?
✅ Good: ≤ 2.5 seconds
⚠️ Needs improvement: 2.5 – 4.0 seconds
❌ Poor: > 4.0 seconds
INP: Interaction to Next Paint
What: How quickly does the page respond to user actions (click, tap, keyboard input)?
✅ Good: ≤ 200 milliseconds
⚠️ Needs improvement: 200 – 500 milliseconds
❌ Poor: > 500 milliseconds
Why important: INP replaced FID (First Input Delay) as a Core Web Vital in 2024. It measures overall interactivity, not just the first input.
CLS: Cumulative Layout Shift
What: How much do visible elements shift during loading?
✅ Good: ≤ 0.1
⚠️ Needs improvement: 0.1 – 0.25
❌ Poor: > 0.25
Impact on SEO & Google Ads
SEO Rankings
Page experience according to Google Search Central:
No single "page experience" ranking signal
Core Web Vitals (LCP, INP, CLS) are used
by Google's ranking systems
Plus self-check points like HTTPS, displaying well
on mobile devices, no intrusive interstitials
→ With similarly good content:
Better page experience can tip the balance
Google retired the Mobile-Friendly Test and the Mobile Usability report in Search Console at the end of 2023. Today you can check how your site displays on mobile with Lighthouse, for example.
Google Ads Quality Score
Landing Page Experience = one of the three Quality Score components
Slow landing page:
→ Visitors leave before they see the offer
→ Weaker landing page experience
→ Lower ad quality, usually a higher CPC
→ Fewer clicks per budget
Fast landing page:
→ Visitors immediately see what the ad promised
→ Better landing page experience
→ Higher ad quality, usually a lower CPC
→ More clicks per budget
Worked example (illustrative numbers, Quality Score never depends on load time alone):
Same keywords, same ad, same budget:
Landing Page A: LCP 5.2s → Quality Score 5 → CPC: €4.50
Landing Page B: LCP 1.8s → Quality Score 8 → CPC: €2.80
Result: around 60% more clicks for the same budget (€4.50 / €2.80)
Optimizing LCP
Most Common LCP Issues
Problem 1: Uncompressed images
❌ hero-image.jpg: 2.4 MB, 4000x3000px
→ Load time: 3.8 seconds (on 4G)
✅ hero-image.webp: 120 KB, 1200x800px
→ Load time: 0.4 seconds (on 4G)
Solution:
<!-- Modern image format + responsive sizes -->
<picture>
<source srcset="hero.avif" type="image/avif">
<source srcset="hero.webp" type="image/webp">
<img src="hero.jpg" alt="..." width="1200" height="800"
loading="eager" fetchpriority="high">
</picture>
Problem 2: Render-blocking CSS/JS
Solution:
<!-- Critical CSS inline in head -->
<style>
/* Only CSS for above-the-fold content */
.hero { ... }
.nav { ... }
</style>
<!-- Load rest async -->
<link rel="preload" href="/styles.css" as="style"
onload="this.onload=null;this.rel='stylesheet'">
Problem 3: Slow server (TTFB)
TTFB (Time to First Byte) targets:
✅ Good: < 200ms
⚠️ OK: 200-500ms
❌ Poor: > 500ms
Solution:
- Use CDN (Cloudflare, Vercel Edge)
- Enable server-side caching
- Optimize database queries
- Upgrade hosting (not the cheapest shared hosting)
Problem 4: Web fonts block rendering
Solution:
<!-- Preload font -->
<link rel="preload" href="/fonts/inter.woff2" as="font"
type="font/woff2" crossorigin>
@font-face {
font-family: 'Inter';
src: url('/fonts/inter.woff2') format('woff2');
font-display: swap; /* Show text immediately, load font later */
}
Optimizing INP
Most Common INP Issues
Problem 1: Heavy JavaScript execution
// ❌ Bad: Everything on main thread
button.addEventListener('click', () => {
processLargeDataset(data); // 500ms heavy computation
updateUI();
});
// ✅ Better: Split with requestAnimationFrame
button.addEventListener('click', () => {
showLoadingState(); // UI updates immediately
requestAnimationFrame(() => {
processLargeDataset(data);
updateUI();
});
});
Problem 2: Too much third-party JavaScript
Typical third-party scripts:
- Google Tag Manager: ~80KB
- Google Analytics: ~45KB
- Facebook Pixel: ~60KB
- Chat widget: ~200KB
- Cookie banner: ~100KB
Total: ~485KB JavaScript → INP killer!
Solution:
- Only load necessary scripts
- Load scripts with defer/async
- Clean up Tag Manager (remove unused tags)
Optimizing CLS
Most Common CLS Issues
Problem 1: Images without dimensions
<!-- ❌ CLS problem: Image has no set size -->
<img src="photo.jpg" alt="...">
<!-- → Space only reserved when image loads → Layout Shift! -->
<!-- ✅ Solution: Specify width and height -->
<img src="photo.jpg" alt="..." width="800" height="600">
<!-- → Browser reserves space in advance → no shift -->
Problem 2: Dynamically injected content
❌ Cookie banner pops in → everything shifts
❌ Ad banner loads late → content jumps down
❌ Chat widget appears → layout changes
Solution:
/* Reserve space for dynamic elements in advance */
.ad-container {
min-height: 250px; /* Reserve space for ad */
}
Quick Wins: Immediately Actionable Optimizations
1. Optimize Images (Biggest Lever!)
✅ Format: WebP or AVIF instead of JPEG/PNG
✅ Compression: 80% quality is usually sufficient
✅ Responsive: Different sizes for different screens
✅ Lazy loading: Lazy load images below viewport
✅ Dimensions: Always specify width/height
Tool: squoosh.app (free, in-browser)
2. Optimize CSS & JavaScript
✅ Critical CSS inline in <head>
✅ Minify CSS/JS
✅ Remove unused CSS/JS
✅ Load scripts with defer or async
✅ Code splitting (only load what's needed)
3. Optimize Server
✅ Use CDN (Cloudflare, Vercel, Netlify)
✅ Set caching headers (Cache-Control)
✅ Enable GZIP/Brotli compression
✅ Enable HTTP/2 or HTTP/3
✅ DNS prefetch for external resources
4. Optimize Fonts
✅ Only load needed font weights (not the whole family)
✅ Use WOFF2 format
✅ Set font-display: swap or optional
✅ Preload most important fonts
✅ Prefer local fonts (system-ui stack)
Checklist: Core Web Vitals Optimization
LCP ✅:
- Hero image compressed (WebP/AVIF, < 200KB)
- Critical CSS inlined
- Fonts preloaded with font-display: swap
- CDN enabled
- TTFB < 200ms
INP ✅:
- JavaScript minimized and split
- Third-party scripts reduced
- Heavy computations offloaded from main thread
- DOM size < 1,500 elements
- Event handlers optimized
CLS ✅:
- All images/videos with width/height
- Space reserved for ads/banners
- Fonts don't cause layout shift
- Dynamic content doesn't shift anything
- No content injection without placeholder
Conclusion
Fast website = better rankings + lower Google Ads costs + more conversions
Priority order:
- Optimize images (biggest single lever)
- Eliminate render-blocking resources
- Enable CDN and caching
- Reduce and optimize JavaScript
- Prevent CLS through dimensions and placeholder reservations
What you can realistically expect: A well-optimized website (all Core Web Vitals green) helps your rankings and your landing page experience, and with that, indirectly, your Google Ads costs. Nobody can honestly promise you fixed percentages for this: how much it brings depends on how slow your site was before and how strong your competition is.
Is your site loading too slowly? Book a free 20-minute intro call and tell me briefly where you stand. If a relaunch is on the cards anyway, you'll find my packages under web development.
FAQ about Website Speed & Core Web Vitals
What are Core Web Vitals and why do they matter?
Core Web Vitals are three Google-defined metrics: LCP (loading speed), INP (responsiveness) and CLS (visual stability). They measure the actual user experience on your website. Since 2021, they're an official Google ranking factor. Websites with good Core Web Vitals have better chances of higher organic rankings and lower Google Ads CPCs.
How do I measure my Core Web Vitals?
Best with PageSpeed Insights (pagespeed.web.dev). There you'll see both real user data and simulation results. Google Search Console shows overall performance of all URLs. For detailed analysis: Chrome DevTools (Lighthouse tab). All tools are free.
What's the most important quick win for better performance?
Optimize images! This is almost always the single biggest lever. Convert images to WebP or AVIF, compress to 80% quality, use responsive sizes (srcset) and lazy load images below the viewport. If large, uncompressed images were the bottleneck, in my experience LCP often improves noticeably from that alone.
Do Core Web Vitals affect my Google Ads Quality Score?
Indirectly yes. Landing page experience is one of the three Quality Score components, and Google explicitly lists faster loading as a way to improve it. A slow page loses visitors before they see your offer, which weakens exactly this component. Because Google considers ad quality in every auction and, according to Google, higher quality ads typically cost less per click, a fast landing page can indirectly lower your CPC. How much depends on your account and your competition.
How often should I check Core Web Vitals?
Monthly in Google Search Console. After every major website change (new design, new features, plugin updates) test immediately with PageSpeed Insights. Especially after adding new third-party scripts (chat, tracking, ads). These are frequently INP killers.
What if my CMS (WordPress etc.) is slow?
5 immediate actions: 1) Install caching plugin (WP Rocket, W3 Total Cache), 2) Auto-convert images to WebP (ShortPixel, Imagify), 3) Deactivate and delete unused plugins, 4) Enable CDN (Cloudflare Free), 5) Update PHP version. If that's not enough: Upgrade hosting from shared to managed WordPress hosting.
