DIY guide
Low Score in Google PageSpeed Insights or Lighthouse Mobile Test?
Updated October 15, 2026
A low mobile score can be discouraging, but the number alone does not tell you what to do. This guide helps you read the result, pick the right problem to fix first, and set realistic expectations.
Why mobile scores are lower
The mobile test simulates a mid-range phone on a slow mobile connection. Your site loads in that harsher environment, so the score is almost always lower than the desktop score. That is intentional: many of your visitors are on phones.
Lab data and real-user data are different
The score at the top of the report is lab data, one simulated test. Above it you may see field data, measured from real visitors over 28 days. Google uses real-user Core Web Vitals, so check the “Core Web Vitals Assessment” first. A site can pass it with a modest lab score, and the lab score can move a few points between runs. Test three times and compare the average.
What drives the score
Lighthouse combines several metrics. At the time of writing, Total Blocking Time counts for 30%, and Largest Contentful Paint and Cumulative Layout Shift for 25% each, with First Contentful Paint and Speed Index making up the rest. In practice that means heavy JavaScript, large hero images and layout jumps do most of the damage.
Match what you see to the right fix
- Slow Largest Contentful Paint: read the LCP guide.
- Slow First Contentful Paint or render-blocking requests: read the FCP guide.
- Slow server response: read the TTFB guide.
- Enormous network payloads: read the payload guide.
- High Total Blocking Time: reduce JavaScript. Remove unused plugins, defer chat widgets and marketing tags, and replace heavy sliders and animations.
- Layout shift (CLS): set width and height on images and videos, reserve space for ads and embeds, and avoid inserting content above what is already on screen.
Set a realistic target
Green scores (90 or more) are achievable on many sites, but not every site. Heavy page builders, ad networks, chat widgets and tracking scripts can cap the mobile score. Aim to pass the Core Web Vitals, remove the largest problems first, and fix one thing at a time so you can see what helped.
Want a second pair of eyes?
Run the free Core Web Vitals report to see your numbers and the biggest opportunities in one place.
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