TL;DR
Core Web Vitals are three Google-defined performance metrics that measure real-world user experience: LCP (how fast the main content loads), CLS (how stable the page is visually), and INP (how responsive it is to interaction). Google uses them as ranking signals — pages that pass all three thresholds get a search ranking boost. Target: LCP under 2.5 seconds, CLS under 0.1, INP under 200 milliseconds.
The Three Core Web Vitals
LCP — Largest Contentful Paint
What it measures: How long until the largest visible element (usually a hero image or main heading) is fully rendered on screen.
Why it matters: LCP is the user’s perception of “when did the page load?” A slow LCP feels like a slow page, even if everything else is fast.
| Score | LCP Value |
|---|---|
| Good | < 2.5 seconds |
| Needs improvement | 2.5–4 seconds |
| Poor | > 4 seconds |
Most common cause of failure: Large, unoptimised hero images. Converting to WebP and adding fetchpriority="high" to the LCP image typically improves this metric significantly.
CLS — Cumulative Layout Shift
What it measures: How much page elements unexpectedly move during load. A score of 0 means nothing moved; higher scores indicate more visual instability.
Why it matters: Layout shifts cause users to misclick, lose their place, or accidentally tap the wrong button. The classic example: reading an article, an ad loads above the text, everything jumps, you tap a link you didn’t mean to.
| Score | CLS Value |
|---|---|
| Good | < 0.1 |
| Needs improvement | 0.1–0.25 |
| Poor | > 0.25 |
Most common cause of failure: Images without explicit width and height attributes. The browser doesn’t know how much space to reserve, so the layout shifts when the image loads.
INP — Interaction to Next Paint
What it measures: The delay between any user interaction (click, tap, keypress) and the next visual update from the page. INP replaced FID (First Input Delay) in March 2024.
Why it matters: A high INP means the page feels unresponsive. Users click a button and nothing seems to happen — or it takes 500ms for the page to react. This is especially damaging on mobile.
| Score | INP Value |
|---|---|
| Good | < 200ms |
| Needs improvement | 200–500ms |
| Poor | > 500ms |
Most common cause of failure: JavaScript-heavy pages with long main thread tasks. Heavy analytics scripts, A/B testing tools, and large React components blocking the main thread all contribute.
How Google Uses Core Web Vitals for Rankings
Google added Core Web Vitals as ranking signals through the “page experience” update in 2021, and continued to refine their weight in subsequent updates.
Their current role: a tiebreaker signal. When two pages are equally relevant to a search query, the one with better Core Web Vitals tends to rank higher. Content relevance and authority remain the dominant signals.
In competitive niches, the difference between 70 and 95 on these metrics can be a real ranking advantage. In uncompetitive niches, the impact is smaller.
How to Check Your Core Web Vitals
For your own site:
- Google Search Console → Core Web Vitals report (real-user data from Chrome users — most important)
- PageSpeed Insights — lab + field data for any URL
- Chrome DevTools → Lighthouse tab → run audit
For any URL:
- PageSpeed Insights (free, no account needed)
- WebPageTest.org (more detailed waterfall analysis)
Always prioritise field data (real users) over lab data (simulated). A page can score 95 in Lighthouse but fail in the field due to real device performance, slow connections, or browser extensions.
What Scores Should You Target?
Minimum acceptable (no ranking penalty):
- LCP: under 2.5s
- CLS: under 0.1
- INP: under 200ms
Competitive target (ranking advantage):
- LCP: under 1.5s
- CLS: under 0.05
- INP: under 100ms
Modern Next.js or Astro sites built with performance in mind routinely achieve 95–100 on Lighthouse with these field data scores.
Frequently Asked Questions
Do Core Web Vitals affect all websites equally?
Yes, but the competitive impact varies. In highly competitive search results, CWV can be a meaningful differentiator. For low-competition long-tail keywords, content quality matters more than performance scores.
My site passes Lighthouse but fails in Search Console. Why?
Lighthouse uses a simulated throttled device. Search Console collects real data from Chrome users on your site — real devices, real connections, real browser state. These differ. Fix the real-user data, not the lab score.
How often do Google’s CWV thresholds change?
Google typically updates thresholds annually, announced via the Chrome developer blog. The current thresholds (LCP < 2.5s, CLS < 0.1, INP < 200ms) were stable as of 2026.
Will improving Core Web Vitals guarantee better rankings?
No. They’re one signal among hundreds. Improving CWV on a site with thin content won’t overcome a content quality disadvantage. But combined with good content, technical performance improvements compound over time.
Final Thoughts
Core Web Vitals are measurable, fixable engineering problems. For any business where organic search drives meaningful traffic, passing all three thresholds should be a non-negotiable baseline.
We build and optimise sites to pass Core Web Vitals by design →