To fix poor Core Web Vitals, check PageSpeed Insights field data for which metric fails (LCP, INP, or CLS), then apply targeted fixes: optimise the LCP image and server speed for LCP; reduce JavaScript work for INP; set image dimensions and reserve ad space for CLS. Re-scan until all three are in the "good" range.
Core Web Vitals are Google's three real-user experience metrics. Failing any one can hurt page experience signals. This guide helps you identify which metric is failing and routes you to the right fixes without guessing.
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Business impact
Poor Core Web Vitals mean a site that feels slow, janky or unstable — visitors notice and leave. Google uses these metrics in page experience evaluation, so fixing them helps both conversions and search performance.
Why this happens
Thresholds (good): LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1. Check field data (CrUX) in PageSpeed Insights — lab data alone can mislead. LCP fixes: fast TTFB, optimised hero image, preload LCP resource. INP fixes: less main-thread JS, break up long tasks. CLS fixes: width/height on images, reserve space for ads/embeds, avoid injecting content above existing content.
How to confirm the issue
Manually: PageSpeed Insights → Core Web Vitals assessment (field data section).
With Plexa Trust: "Poor PageSpeed Score" and related findings; re-scan after fixes.
Step-by-step fix
Identify which metric(s) fail in field data — LCP, INP, or CLS.
For LCP: improve TTFB, compress/preload the hero image, remove render-blocking resources.
For INP: defer JS, reduce third parties, split long tasks.
For CLS: set dimensions on images/video, reserve ad slots, use font-display: swap carefully.
Deploy fixes and wait for field data to update (days to weeks).
Re-scan and re-test in PageSpeed Insights.
Platform-specific fixes
All platforms
Core Web Vitals fixes are largely platform-agnostic.
Use PageSpeed Insights "Opportunities" and "Diagnostics" per failing metric.
Follow our dedicated fix guides for LCP, INP, and CLS for deep dives.
Prioritise mobile — Google uses mobile-first indexing.
WordPress
Combine caching plugin + image optimisation + script deferral.
Avoid layout-shifting ad plugins without reserved space.
How to verify the fix
Trust field data over lab scores for go/no-go decisions.
Fix the worst metric first if resources are limited.
Test on real mobile devices, not only desktop.
Common mistakes
Chasing a green lab score while field data stays red.
Fixing only LCP and ignoring CLS or INP.
Deploying changes without measuring before/after.
Frequently asked questions
What are the three Core Web Vitals?
LCP (loading), INP (responsiveness), and CLS (visual stability).
Which matters most?
All three matter for page experience. Fix whichever fails field data first.
How long until field data updates?
CrUX data updates on a rolling 28-day window — improvements take time to show.
Is INP the same as FID?
INP replaced FID as a Core Web Vital in 2024. INP measures responsiveness across the whole visit.
Do plugins fix Core Web Vitals automatically?
Caching and image plugins help, but CLS and INP often need theme and script changes too.
Where do I see field data?
PageSpeed Insights, Search Console → Experience → Core Web Vitals.
Can good hosting fix all vitals?
It helps LCP/TTFB but not CLS from missing image dimensions or INP from heavy JavaScript.
How do I confirm it worked?
Field data moves to "good" in Search Console; PageSpeed and Plexa Trust scores improve.
Think you've fixed it?
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