Core Web Vitals Explained for Business Owners

The Three Metrics and What They Measure

Largest Contentful Paint (LCP) measures how long it takes for the most significant visible element on your page to load — typically a hero image, a large heading, or a video. Google's target is under 2.5 seconds. Sites that take longer are considered to be providing a poor experience, and their rankings reflect it.

Cumulative Layout Shift (CLS) measures visual stability. Have you ever clicked a link on a mobile page only to have the button move as an image loaded above it, causing you to tap something unintended? That experience is what CLS measures. Google targets a score below 0.1. High CLS scores correlate directly with high bounce rates — users leave pages that feel unstable and untrustworthy.

Interaction to Next Paint (INP) replaced First Input Delay in March 2024. It measures how quickly your page responds to all user interactions — taps, clicks, keyboard input — across the entire session. Google targets under 200 milliseconds. A sluggish, unresponsive page feels broken even if it has technically loaded, and INP captures this experience precisely.

Why This Directly Affects Your Business Revenue

Google's Page Experience algorithm uses Core Web Vitals as a tiebreaker when two pages are equally relevant to a search query. In practice, with millions of pages competing for the same search terms, this tiebreaker matters in nearly every case. Sites with green Core Web Vitals scores outrank identical competitors with poor scores.

The commercial impact of ranking position is measurable. Moving from position 4 to position 2 in a competitive search result approximately triples organic click-through rate. Position 1 commands around 27.6% of all clicks for a given search term. Position 4 commands approximately 7%. The difference compounds — more clicks generate better engagement signals, which reinforce the ranking, which drives more clicks.

Beyond ranking, page speed directly affects conversion. Google's internal research shows a 1-second improvement in mobile load time improves conversion rates by up to 27%. For an e-commerce business turning over £2m annually, a single second of load time improvement is worth approximately £540,000 in additional revenue — without any additional marketing spend.

Common Causes of Poor Core Web Vitals Scores

Most poor Core Web Vitals scores have identifiable, fixable causes. For LCP, the culprit is usually an unoptimised hero image loaded without priority — large file sizes, wrong formats, or a server response time that delays everything following it.

CLS issues almost always originate from images without explicit dimensions, fonts that load after layout has rendered, or dynamic content injected above existing content. These are solvable problems, not inherent to having a visual, content-rich website.

Poor INP is typically caused by excessive JavaScript running on the main thread — often third-party tracking scripts, analytics libraries, or chat widgets executing at the moment a user tries to interact with the page. Each additional script is a competitor for the thread that processes user input.

• Unoptimised images (wrong format, missing dimensions, missing fetchpriority)
• Render-blocking JavaScript and CSS
• Excessive third-party scripts (analytics, chat, advertising)
• Slow server response times (TTFB above 600ms)
• No caching layer or CDN

How to Check Your Own Scores

Google's PageSpeed Insights tool (pagespeed.web.dev) gives you both lab and field data for any URL in under 60 seconds. Enter your homepage and your most commercially important page — the scores often differ significantly. A score above 90 on both mobile and desktop is the target for a competitive website in 2025.

The Chrome User Experience Report (CrUX) provides real-world data from actual Chrome users visiting your site. Google Search Console's Core Web Vitals report surfaces this data directly. The field data reflects what real visitors experience — not just what a simulated test shows. If the two diverge significantly, the field data takes precedence in Google's ranking systems.

A PageSpeed score below 50 on mobile is not a minor issue. It is a measurable, ongoing drag on your search rankings and your conversion rate — every single day.