- Article
- Intermediate
- 2 minutes read
- Reviewed August 4, 2026
- WordPress performance
Core Web Vitals are a current set of field-oriented metrics for loading, interactivity and visual stability.
The metrics are Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift.
Largest Contentful Paint
LCP measures when the largest visible content element is rendered.
A good experience is generally represented by an LCP of 2.5 seconds or less at the 75th percentile.
WordPress causes can include:
- Slow TTFB.
- A late-discovered hero image.
- An oversized image.
- render-blocking CSS.
- web fonts.
- client-rendered content.
- competing high-priority resources.
Interaction to Next Paint
INP evaluates interaction latency across the visit.
A good value is generally 200 milliseconds or less at the 75th percentile.
Common causes include:
- Long JavaScript tasks.
- complex DOM updates.
- excessive event callbacks.
- third-party scripts.
- slow AJAX or REST responses.
- heavy editor or storefront components.
Cumulative Layout Shift
CLS measures unexpected visual movement.
A good value is generally 0.1 or less.
WordPress causes include missing image dimensions, late banners, ads, font swaps, embeds and dynamically inserted notices.
Field and Lab Data
PageSpeed Insights can show field data from real Chrome visits when sufficient data exists and laboratory data from Lighthouse.
Field data identifies real-user patterns. Lab data helps reproduce and debug a test page.
The two can differ because they represent different devices, networks, time periods and interactions.
Page and Origin Data
Review both individual URLs and broader origin trends.
A homepage can pass while templates used by most visitors fail.
Frequently Asked Questions
Is TTFB a Core Web Vital?
No, but it can affect LCP.
Did INP replace FID?
Yes. INP is the current responsiveness Core Web Vital.