If a page feels slow, start with the three Core Web Vitals before installing another optimisation plugin. They measure parts of the experience that real visitors notice: loading, interaction response and visual stability.
The current three are LCP, INP and CLS. Google evaluates the recommended thresholds using field data at the 75th percentile, separately for mobile and desktop where enough data is available.
You do not need to be a performance specialist to understand the basics. Test the important pages on a phone, check the main actions and use field and lab data to find the biggest user-facing problem.
Largest Contentful Paint (LCP)
LCP measures how quickly the largest visible piece of content, such as a hero image or main heading, finishes rendering. A good LCP is 2.5 seconds or less at the 75th percentile.
Between 2.5 and 4 seconds needs improvement. Above 4 seconds is poor. A slow server response, a large hero image, render-blocking resources and third-party scripts can all delay the main content.
Common causes of poor LCP include:
- slow servers
- huge hero images
- render-blocking CSS
- heavy page builders
- slow fonts
- third-party scripts
Interaction to Next Paint (INP)
INP measures how quickly the page responds throughout a visit when someone clicks, taps or types. It is the current Core Web Vital for interaction responsiveness; FID is no longer the current metric.
A good INP is 200 milliseconds or less at the 75th percentile. From 200 to 500 milliseconds needs improvement, while anything above 500 milliseconds is poor.
Poor INP can come from:
- too much JavaScript
- heavy plugins
- complex front-end effects
- third-party widgets
Cumulative Layout Shift (CLS)
CLS measures unexpected movement while a page loads. If a button, heading or cookie banner jumps after you start reading, the layout is unstable.
A good CLS is 0.10 or less at the 75th percentile. From 0.10 to 0.25 needs improvement, and above 0.25 is poor.
Typical causes include:
- images without dimensions
- ads injected late
- fonts changing layout
- banners appearing above existing content
Lab data vs real-user data
Lab tools simulate a device and network so you can reproduce a problem. Field data, such as the data shown in PageSpeed Insights or Search Console when enough traffic exists, comes from real Chrome users. They answer different questions and should not be treated as interchangeable.
Both are useful.
Lab tests help diagnose. Real-user data tells you how visitors actually experience the site.
Does a perfect score matter?
No.
A 100/100 lab score is not the goal by itself. Good Core Web Vitals are recommended, but they do not guarantee rankings. Relevance, content quality, technical accessibility and the usefulness of the page still matter.
Focus on:
- removing obvious bottlenecks
- keeping pages stable
- making interactions responsive
- serving content quickly
WordPress performance priorities
For WordPress, start with:
- good hosting
- image optimisation
- sensible caching
- fewer unnecessary plugins
- lightweight front-end code
- controlled third-party scripts
How SiteForge approaches performance
SiteForge approaches performance as part of the build: responsive layouts, image optimisation, sensible caching, managed hosting and a controlled WordPress setup. We look at the actual page rather than promising that one plugin will solve every problem.
View WordPress website design or WordPress hosting.
Source
Source: Google Search Central: Core Web Vitals (checked 25 August 2026).
How to test Core Web Vitals
Useful tools include:
- Google Search Console
- PageSpeed Insights
- Chrome DevTools
- Lighthouse
Do not panic when two tools show different numbers. They may be measuring different devices, networks or data sources.
What should a business fix first?
Start with the biggest user-facing problems.
Examples:
- compress a huge hero image
- remove a chat widget nobody uses
- fix an unstable cookie banner
- reduce unnecessary JavaScript
- improve slow hosting
- preload a genuinely critical font or image where appropriate
Avoid installing several optimisation plugins that all attempt to do the same thing.
Frequently Asked Questions
Are Core Web Vitals a Google ranking factor?
Google includes Core Web Vitals within its broader page-experience considerations, but good scores do not guarantee rankings.
Is mobile performance more important?
Many business websites receive significant mobile traffic, so mobile testing is essential. Search Console field data is particularly useful when available.
Can a plugin fix Core Web Vitals?
Sometimes a caching or optimisation plugin helps, but it cannot fix every root cause. Hosting, theme architecture, images and third-party scripts also matter.
Should I remove all animations?
No. Use animation selectively and avoid effects that delay interaction, cause layout shifts or make content difficult to use.
