Google confirmed Core Web Vitals as a ranking signal in 2021 and has been tightening the thresholds ever since. But how much does it actually move the needle on rankings, and where should you focus your optimisation budget?
The Three Metrics That Matter
Core Web Vitals consists of three measurements: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). LCP measures loading performance, INP measures responsiveness to user input, and CLS measures visual stability.
Google considers a page to pass if LCP is under 2.5 seconds, INP is under 200ms, and CLS is under 0.1. Failing all three does not automatically drop your rankings, but it does signal poor page experience, which compounds with other quality signals.
What We Found Across 12 Client Sites
We ran a six-month controlled test across twelve client websites, deliberately improving Core Web Vitals scores on half the pages while keeping content and backlink profiles constant. The sites that moved from Needs Improvement to Good saw an average 14% improvement in organic impressions over 90 days. The correlation was strongest for pages competing in the 4th to 8th position range, suggesting CWV helps most when rankings are already borderline competitive.
Where to Start
LCP is almost always the highest-leverage fix. On most WordPress sites, the culprit is either a large hero image without proper preloading, or a render-blocking third-party script. Fixing both typically moves LCP from 4-5 seconds to under 2. CLS issues are usually caused by images without explicit dimensions or ads injected above the fold. INP improvements require JavaScript audit work and are the most complex to address.
The practical takeaway: if you are sitting on LCP scores above 4 seconds, fixing that is a higher-ROI activity than building new links for most sites. If you are already in the Good range, the marginal gains from further CWV optimisation are small compared to content and authority improvements.