Core Web Vitals: What They Are and How They Affect Your Ranking

In 2021, Google confirmed what many had already suspected: user experience is a direct ranking factor. The Core Web Vitals are the metrics that Google uses to measure this experience — and sites that do not meet the recommended thresholds lose positions, regardless of content quality.

In this guide, you will understand what Core Web Vitals are, how each metric affects your site’s SEO, and what the most effective actions are to improve the numbers without needing to rewrite all the code.

What Are Core Web Vitals?

Core Web Vitals (CWV) are a set of metrics defined by Google to measure the quality of user experience in three dimensions: loading speed, interactivity, and visual stability. Each dimension has a specific metric with clear thresholds of “good,” “needs improvement,” and “poor.”

Since 2021, CWV has been part of Google’s Page Experience Signal — the set of experience factors that influence ranking. Sites with good CWV have an advantage over competitors with similar content but inferior experience.

The 3 Metrics of Core Web Vitals

1. LCP — Largest Contentful Paint (Loading Speed)

LCP measures how long it takes for the largest visible element on the page — usually a hero image, a main text block, or a video — to appear on the user’s screen after loading begins.

• Good: up to 2.5 seconds
• Needs improvement: between 2.5 and 4 seconds
• Poor: over 4 seconds

LCP is the metric with the greatest perceived impact by the user — it is the moment when the page “seems loaded.” A slow LCP is the main cause of abandonment before interaction.

Main causes of slow LCP and how to fix them:

• Heavy images: use the WebP or AVIF format instead of JPEG/PNG. Compress images before uploading. Use the loading="eager" attribute on the main image above the fold and fetchpriority="high" so the browser prioritizes it.
• Slow server (high TTFB): a high Time to First Byte means the server takes a long time to respond. Switching to a faster server or enabling page caching resolves this in most cases. For WordPress, plugins like WP Rocket or LiteSpeed Cache do this.
• CSS and JavaScript blocking rendering: remove or defer scripts that block the loading of main content. Use the defer attribute on non-critical scripts.

2. INP — Interaction to Next Paint (Interactivity)

INP replaced FID (First Input Delay) in March 2024. It measures the overall responsiveness of the page — how long the page takes to respond to any user interaction (clicks, taps, typing) throughout the entire session, not just the first interaction.

• Good: up to 200 milliseconds
• Needs improvement: between 200 and 500 ms
• Poor: over 500 ms

A poor INP is especially critical on entry-level mobile devices — where the processor is less powerful and any heavy JavaScript causes noticeable stutters.

How to improve INP:

• Reduce and defer third-party JavaScript (chat widgets, heavy analytics scripts, pop-ups).
• Avoid long tasks on the main thread — break heavy scripts into smaller parts using the scheduler.yield() API or setTimeout.
• Remove unnecessary plugins in WordPress — each installed and active plugin can contribute scripts that degrade INP.

3. CLS — Cumulative Layout Shift (Visual Stability)

CLS measures the amount of unexpected shifting of elements on the page during loading. You know when you’re about to click a button and it moves because an ad loaded above? That’s layout shift — and it’s exactly what Google penalizes.

• Good: up to 0.1
• Needs improvement: between 0.1 and 0.25
• Poor: over 0.25

Common causes of high CLS and how to fix them:

• Images without declared dimensions: always set the width and height attributes on <img> tags. The browser reserves space before the image loads and eliminates the shift.
• Ads and embeds without reserved space: variable-size elements (banners, YouTube iframes) should have a minimum reserved space via CSS before loading.
• Custom fonts causing FOUT: when the web font replaces the fallback font, the text may shift. Use font-display: swap with adjusted fallback metrics to minimize the jump.

How to Measure Your Site’s Core Web Vitals

Google offers free tools to measure CWV with real data and lab data:

• Google Search Console → Page Experience Report: shows CWV with real user data (field) grouped by URL. It is the most important source because it uses the same data that Google uses for ranking.
• PageSpeed Insights: analyzes a specific URL and shows both field data (when available) and lab data with detailed diagnostics of each issue.
• Chrome DevTools → Lighthouse: local tool for testing during development. Simulates loading on slow connections and mobile devices.
• Web Vitals Extension: Chrome extension that shows CWV in real-time as you browse your site’s pages.

Important: there is a difference between lab data (simulated) and field data (real users). Google uses field data for ranking. A site may appear fast on PageSpeed Insights and still have poor CWV on Search Console if real users face different conditions than those simulated.

Core Web Vitals in WordPress: The Most Impactful Actions

Most Brazilian company websites run on WordPress. In this context, these are the actions with the highest return in improving CWV:

1. Page caching plugin: WP Rocket, LiteSpeed Cache, or W3 Total Cache reduce TTFB and improve LCP with simple configuration. Impact: high.
2. CDN (Content Delivery Network): distributes static files (images, CSS, JS) through servers close to the user. Cloudflare offers a free plan with an efficient CDN for WordPress. Impact: high for users geographically distant from the server.
3. Image compression and conversion: Imagify, ShortPixel, or Smush plugins automatically convert images to WebP and compress them without noticeable quality loss. Impact: very high for sites with heavy images.
4. Proper hosting: cheap shared hosting is the root cause of high TTFB on many WordPress sites. Migrating to managed WordPress hosting (like Kinsta, WP Engine, or Cloudways) structurally resolves the issue. Impact: very high.
5. Remove unnecessary plugins: each installed and active plugin adds scripts. Conduct an audit and disable what is not essential. Impact: medium to high depending on the plugins.

What is the Real Impact of Core Web Vitals on Ranking?

Google confirms that CWV is a ranking factor, but it is a tiebreaker factor — not a dominant one. This means:

• A page with excellent content but poor CWV can still rank above a page with perfect CWV but weak content.
• Among pages of similar quality, CWV can be the deciding factor for which appears first.
• Poor CWV indirectly impact SEO even beyond ranking: high bounce rates, low session time, and fewer conversions are negative behavioral signals that Google also observes.

In practice, optimizing Core Web Vitals is one of the few technical SEO improvements that has a dual impact: it directly improves ranking and enhances conversions because users have a better experience.

To delve deeper into technical SEO strategy as a whole, access the guide What is SEO? Complete Guide or learn about the Focofy SEO service for websites, which includes technical auditing and Core Web Vitals optimization.

Conclusion

Core Web Vitals are not abstract technical metrics — they are the quantitative translation of the experience your user has when accessing the site. Slow LCP makes the visitor give up before seeing the content. High INP makes the site seem frozen. High CLS makes the user click in the wrong place by mistake.

Improving CWV is one of the optimizations with the best cost-benefit ratio in SEO: diagnostic tools are free, the most impactful fixes (caching, image compression, CDN) are accessible even for small sites, and the results show up in both ranking and the real experience of visitors.

Want to know how your site’s Core Web Vitals are doing and what to prioritize for improvement? Access the complete guide at SEO for Companies or talk to our team for a free technical diagnosis.