A page that feels fine on your laptop can be slow on a phone, because phones have slower processors and can have slower connections. On a slow page, some visitors leave before they read anything.
This guide gives the targets to aim for, how to measure them, and the usual causes with a fix for each.
The three numbers Google uses
Google measures speed and stability with three Core Web Vitals. These are the limits it calls good:
- Largest Contentful Paint (LCP): 2.5 seconds or less. How quickly the main content appears.
- Interaction to Next Paint (INP): 200 milliseconds or less. How quickly the page reacts when someone taps or clicks.
- Cumulative Layout Shift (CLS): 0.1 or less. How much the layout jumps around while loading.
Google assesses them at the 75th percentile of page loads, separately for mobile and desktop. In plain terms, three out of four visits need to be at or under each limit.
Test your site the way a phone sees it
- Open PageSpeed Insights at pagespeed.web.dev and paste your address.
- Choose the Mobile tab.
- Look for real-user results first. They appear when enough people have visited the page, or your site as a whole. If there isn't enough data, you will see lab results only.
- Run the test a few times. Lab results vary from run to run, so look for the pattern and not a single number.
The usual causes, and how to fix each
- Oversized images. A photo straight from a camera can be many times bigger than the space it fills. Resize it to the size shown, compress it, use a modern format such as WebP or AVIF, and set its width and height so the page doesn't jump when it loads.
- Fonts and scripts that block the first screen. Custom fonts and scripts that must load before anything shows delay the first paint. Use fewer font files and weights, and defer scripts that aren't needed straight away.
- Third-party scripts. Chat widgets, analytics, tracking pixels and embeds each add code the phone has to run. Remove the ones you don't use and load the rest after the page is usable.
- Too much JavaScript. Heavy pages can ask a phone to do a lot of work before a tap gets a response. This is what INP measures.
- Layout jumps. Images without sizes, banners that appear late and fonts that swap in cause CLS. Reserve space for anything that loads late.
- A slow first response. If the server takes a long time to answer, everything after it is late. Static pages served from a content delivery network avoid this.
- Autoplay video and heavy animation. Both cost a lot on a phone. Load video only when someone chooses to play it.
What you can and can't fix inside a builder
Check what your builder lets you change. Some let you resize images and remove widgets, but not change how the page's code loads or reduce the amount of code they add. If you have done the easy fixes and the numbers are still over the limits, the remaining cost may be in the platform. Then the options are to live with it or to rebuild.
We test our own pages against these limits. When we last checked, on 20 September 2026, lab tests on a simulated mobile connection gave them 97 or higher for performance, with the main content appearing in under 2.5 seconds and no layout shift. Lab results can differ from real-user data, so treat them as a guide.
Our Fix & Launch service starts at $450. We measure on mobile, fix images, fonts, scripts and layout, and send you before and after numbers. If the platform is the limit, we tell you plainly.
Ask us to fix your slow site