Why page experience became a ranking signal
Google has always cared about page speed in theory. But for years it was difficult to measure consistently — load time varied too much depending on conditions, devices, and what you chose to measure.
Core Web Vitals changed that. Introduced as ranking signals in 2021, they gave Google a standardised set of measurements that reflect real-world user experience rather than synthetic lab tests. They also gave site owners clear, actionable targets to aim for.
Understanding what each metric actually measures makes the targets easier to hit — and helps you prioritise fixes that move rankings rather than just improve numbers in a report.
The three metrics that matter
LCP — Largest Contentful Paint
LCP measures how long it takes for the largest visible element on the page to fully render. That's usually a hero image, a large heading, or a prominent block of text.
Target: under 2.5 seconds.
Poor LCP is the most common Core Web Vitals issue we find, and it almost always comes down to the same causes: unoptimised images, render-blocking resources, or slow server response times. Fixing it usually means compressing and properly sizing images, converting to next-gen formats like WebP, and removing or deferring scripts that block the main thread.
CLS — Cumulative Layout Shift
CLS measures visual instability — how much the page layout shifts as it loads. When elements jump around after the initial render (because an image loaded without defined dimensions, or an ad appeared above existing content), CLS goes up.
Target: under 0.1.
The fix is usually simple: always define explicit width and height on images and embeds. This lets the browser reserve space before the element loads, preventing content from shifting.
INP — Interaction to Next Paint
INP replaced FID (First Input Delay) as the third Core Web Vital in March 2024. Where FID only measured the delay on the very first interaction, INP measures the responsiveness of all interactions throughout the page session — clicks, taps, keyboard inputs.
Target: under 200 milliseconds.
Poor INP usually points to heavy JavaScript execution on the main thread. The browser can't respond to user inputs while it's busy running scripts. Auditing and reducing JavaScript payload — or deferring non-critical scripts — is the main lever.
How to check your scores
Two tools are worth using together:
PageSpeed Insights runs a real-world test using field data from Chrome users if your site has enough traffic, and a lab test if it doesn't. It gives you both and flags which elements are causing issues.
Google Search Console — the Core Web Vitals report shows you which pages are failing in the real world, not just in a test environment. A page can look fine in PageSpeed Insights but have poor field data because of how real users on real devices actually experience it.
The gap between lab and field data is worth paying attention to. Mobile performance is almost always worse than desktop. Fix for mobile first.
What's actually worth fixing
Not every poor Core Web Vitals score needs a full rebuild. In our experience, most sites reach "good" thresholds by addressing a short list of issues:
- Image optimisation — compress images, define dimensions, switch to WebP or AVIF, use lazy loading for below-the-fold assets
- Render-blocking scripts — audit what's loading in the
<head>and defer anything non-critical - Third-party scripts — tag managers, chat widgets, and tracking pixels often cause more performance damage than the first-party site itself
- Font loading — use
font-display: swapand preload critical fonts to prevent invisible text during load
These fixes don't require rebuilding your site. They require auditing what's there and removing or deferring what doesn't need to be there.
The bottom line
Core Web Vitals are a ranking signal, but treating them purely as a ranking exercise misses the point. A faster, more stable page converts better. Users who don't experience layout shifts and sluggish interactions are more likely to stay, read, and enquire.
The ranking benefit and the user experience benefit point in the same direction. That's rare enough in SEO that it's worth taking seriously.
