Skip to content
Permo Docs

Lighthouse Performance score

The Performance score is the big number at the top of a PageSpeed Insights report, from 0 to 100. It sums up how quickly and smoothly the page loaded in Google’s lab test: how soon content appeared, how long the browser was too busy to react, and how much the layout moved.

Why it matters

Section titled “Why it matters”

The score is an easy way to see at a glance whether a page is in good shape and whether a change helped. It’s a summary of one simulated test, though, not a measure of what every visitor experiences. A page can score 60 in the lab and still feel fast for most real visitors on good phones and connections, which field data would show.

How the score is calculated

Section titled “How the score is calculated”

Lighthouse measures five metrics, turns each into a score between 0 and 100 based on how the page compares with real websites, and then takes a weighted average:

The findings in the report don’t count directly. Fixing one helps the score only if it improves one of these metrics.

Because of the weights, one Poor metric among Total Blocking Time, Largest Contentful Paint and Cumulative Layout Shift keeps the score below 90, even if everything else is perfect. Only First Contentful Paint or Speed Index can be Poor while the overall score is still Good. And when all five metrics are Good, the score is always Good too.

The scoring curve also flattens out at the top: going from 99 to 100 takes about as much improvement as going from 90 to 94.

What influences it

Section titled “What influences it”

Browser: The most common reason for a low mobile score on WordPress sites is JavaScript. Themes, page builders, sliders, chat widgets and tracking scripts all add code that the simulated phone needs a long time to run, and that drives up Total Blocking Time, the metric with the largest weight. Large images and stylesheets that block the first content push back the paint metrics.

Cache: Without a page cache, WordPress builds the page for every request, so content starts arriving later and the paint metrics suffer.

Server: A slow or busy server delays the first response, and everything else waits for it.

WordPress: Every active plugin that adds something to the front end, such as a stylesheet, a script, a font or an embed, adds to the work for each page.

CDN: Serving images and files from a location close to the test machine shortens their download time.

In Permo

Section titled “In Permo”

Permo shows the Performance score as a ring for each device, Mobile and Desktop, colored by Google’s three ratings. It also shows a trend: Permo compares the score with the median of the previous checks (up to five) and shows an arrow when the difference is 5 points or more. Smaller changes are normal from test to test.

Reference values

Section titled “Reference values”

In Lighthouse 13.5, the five metrics count as follows: Total Blocking Time 30%, Largest Contentful Paint 25%, Cumulative Layout Shift 25%, First Contentful Paint 10% and Speed Index 10% (source: Lighthouse performance scoring and Lighthouse default configuration, v13.5.0, accessed October 16, 2026). Google adjusts the weights from time to time.

Section titled “Related”

Sources