Methodology · Website

How the Core Web Vitals is calculated

Method version performance-v3 · Last updated 2026-10-13

In short

Core Web Vitals are Google's real-user measurements of loading (Largest Contentful Paint), responsiveness (Interaction to Next Paint) and visual stability (Cumulative Layout Shift). Actavero shows the 75th-percentile values from the Chrome User Experience Report and Google's overall assessment of whether a site passes.

Formula

Each metric is the 75th percentile of real Chrome users over the last 28 days.
Good: LCP ≤ 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1. Poor: LCP > 4 s, INP > 500 ms, CLS > 0.25.
A page passes when all three metrics are good.

How it is calculated, step by step

Request the field data of the URL (or, when a page has too little traffic, the whole origin) from the PageSpeed Insights API.
Read the 75th-percentile value and Google's category for each metric.
Show the overall assessment next to the lab-based Website score.

What goes into it

Largest Contentful Paint (LCP): Time until the largest visible element has rendered.
Interaction to Next Paint (INP): Delay between a user interaction and the next visual update.
Cumulative Layout Shift (CLS): How much visible content moves unexpectedly while loading.

Data sources

Chrome User Experience Report (CrUX) through the PageSpeed Insights API

How often it is updated

With every Website score measurement; the data itself is a rolling 28-day window.

How to read it

Core Web Vitals are a Google ranking signal and reflect what real visitors experience.
A site can have a mediocre lab score but pass Core Web Vitals, or the other way round; both views are useful.

Limitations

Only available for pages and sites with enough Chrome traffic; small sites often have no field data.
The data lags: it covers the previous 28 days.

Frequently asked questions

Why is there no Core Web Vitals data for a site?

Google only publishes field data when enough Chrome users visited the page or site in the last 28 days.

Which percentile is used?

The 75th percentile, as Google does: three quarters of visits are at least this fast.

Website score — Google Lighthouse performance (0–100) of the homepage and up to four representative pages, weighted: homepage 40%, the other pages share 60%.