the performance results of my Webflow page via Google’s Page Speed Insights fluctuate strongly and randomly between 75 and 98. And that’s when I run the tests right after each other from the same device and location. So it changes within seconds.
I have been working with two specialized Webflow developers (one of them from the Webflow network) for several weeks to push the results consistently (!) to a value > 95, but neither developer can tell me why the values continue to fluctuate. I know that some fluctuation can happen, but almost 25% i unusual and I’m worried, this harms my SEO performance. Unfortunately I can’t share the screenrecording here, but I could add the screenshots of the two different results if this helpts.
Does anyone here have an idea why the fluctuations occur and even more important: how they can be eliminated?
This fluctuation in the lab test score is unlikely to be directly harming your SEO performance. Google uses the Core Web Vitals (CWV) as a ranking signal. The data for this comes from the Chrome User Experience Report (CrUX), which is aggregated data from real users visiting your site over the last 28 days. This is called Field Data.
The score you see immediately after running a test is Lab Data, generated by a tool called Lighthouse. It runs a one-time test from a Google server on a simulated device with a throttled network connection.
Lab Data (your fluctuating score): A diagnostic tool to help you identify potential issues.
Field Data (the CrUX report): What Google actually uses for ranking. This data is much more stable.
You should be more concerned if the “Core Web Vitals Assessment” at the top of your PageSpeed Insights report shows “Failed” based on real-user data.
Speed Variance
The “random” nature of the score comes from the fact that the web is a dynamic environment. Even in a simulated “lab,” conditions are never 100% identical from one second to the next.
While PageSpeed Insights is essential, for debugging I highly recommend https://www.webpagetest.org/. It allows you to run a test with multiple runs (e.g., 5) and will give you a median result, which ignores the outliers. Its waterfall chart is also far more detailed for pinpointing exactly which resource is causing a slowdown on a specific run.
I treat the PageSpeed score not as a fixed number, but as a diagnostic check-up. The variability you’re seeing is likely caused by server response times and third-party scripts. To improve consistency, focus on deferring non-critical JavaScript and optimizing the loading of your LCP element. And remember to pay more attention to your Field Data (Core Web Vitals) for a true picture of SEO impact.
Thank you very much for your quick and detailed response. The webpagetest results look good. Consequently, I can (and must) accept the fluctuations in the lab data.
I understand the frustration of seeing such fluctuating results in PageSpeed Insights It can be concerning, especially when you’re trying to consistently achieve high performance and ensure it doesn’t impact your SEO.The fluctuations in your PageSpeed Insights scores, ranging from 75 to 98, are caused by variable network conditions, server load, third-party resources, or browser caching behaviors. These fluctuations can also happen due to temporary delays in loading assets or fluctuations in server response times when testing multiple times.
You can do few things:
Run multiple tests at different times and average the results to get a more consistent reading. Ensure consistent test conditions for the same device, network, and browser. Optimize caching to ensure assets are cached and loaded properly. Defer non-essential third-party scripts to improve initial load times.
To get a handle on consistent performance, you can also take a look into the Website Speedy App which helps monitor and optimize page speed in the background. This way, you’ll have continuous insights into how your site performs, without worrying about sudden fluctuations during isolated tests.