How Core Web Vitals affect SEO
Google Search rankings use real-user Core Web Vitals field data—not Lighthouse scores. Optimize LCP, INP, and CLS for the 75th percentile of Chrome users, while using Lighthouse as a diagnostic tool.
How Core Web Vitals affect SEO
Author: Malte Ubl and Alice Alexandra Moore | Published: 2024-01-19 | Generated: 2025-07-05 | Domain: vercel.com
Tags: ‘#seo’ ‘#core-web-vitals’ ‘#lighthouse’ ‘#web-performance’ ‘#google-search’
TLDR
Google’s Page Experience ranking system uses only real-user Core Web Vitals field data—Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS)—not Lighthouse scores. These metrics are evaluated at the 75th percentile over a rolling 28-day window, grouped with similarly performing pages, and ranked separately for mobile and desktop. Lighthouse remains useful for diagnosing likely performance, accessibility, best-practice, and technical-SEO problems, but its synthetic score does not directly affect search ranking.
Key Takeaways
- Field data drives performance-based ranking: Google uses CrUX data from real Chrome users to assess LCP, INP, and CLS; Lighthouse and its overall performance score are not ranking inputs.
- Page experience is a secondary factor: Query relevance and content quality matter substantially more, but Core Web Vitals can break ties between similarly relevant competitors while also improving conversion through better UX.
- Google evaluates P75 over 28 days: Search Console and PageSpeed Insights report the 75th-percentile experience of users over a 28-day sliding window, so improvements and regressions can take up to a month to fully appear.
- CrUX has coverage limitations: Data includes eligible, sufficiently popular public pages visited by opted-in signed-in Chrome users on desktop or Android; iPhone users are excluded. Pages without enough field data are not measured for this ranking factor.
- Lighthouse is diagnostic, not authoritative: Its performance score combines FCP, Speed Index, LCP, Total Blocking Time, and CLS; actual Core Web Vitals account for only 50% of the weighted score, and INP is excluded.
- Speed Insights shortens feedback cycles: Vercel’s tooling reports real-user metrics in near real time and supports route, deployment, branch, percentile (P75/P90/P95/P99), time-window, and geographic filtering.
Images & Media
- Google Search Console Core Web Vitals report — Search Console interface for reviewing site-wide Core Web Vitals status.
- PageSpeed Insights Core Web Vitals results — Mobile field-data report illustrating the real-user metrics used for ranking.
- Vercel Speed Insights dashboard — Project-level chart for monitoring real-user performance metrics.
- Speed Insights geographic P75 map — Country-level visualization of P75 scores and relative data volume.
Referenced Links
- Google Core Web Vitals documentation — Google’s overview of the metrics used in Page Experience evaluation.
- Google Search Console — Authoritative reporting source for a site’s search performance and Core Web Vitals status.
- PageSpeed Insights — Displays both Chrome field data and Lighthouse lab diagnostics for individual pages.
- Chrome User Experience Report (CrUX) — Public dataset and program behind Google’s Core Web Vitals field data.
- Lighthouse performance scoring — Details the weighted synthetic metrics comprising Lighthouse’s performance score.
- Vercel Speed Insights documentation — Documentation for real-user Core Web Vitals monitoring with granular filters.