At Spindogs, we’re often asked by clients about their website’s PageSpeed Insights results. For those unfamiliar, PageSpeed Insights is the go-to tool for measuring website speed – and as part of the Google suite, it can impact both organic and paid search rankings.
Why do Page Speed Insights scores vary so much?
If you’ve ever run your website through PageSpeed Insights, you’ve probably noticed:
- Your desktop score looks great – often in the 90s, maybe even close to perfect.
- Your mobile score, on the other hand? It’s inconsistent. One test says 90, the next says 55, then it jumps to 70.
So, what’s going on? And should you be worried?
Desktop vs Mobile scores: why they’re different
PageSpeed Insights doesn’t just test your site once – it runs two separate audits:
- Desktop: Tests your site in an ideal scenario – fast broadband, powerful computer, no CPU throttling.
- Mobile: Puts your site through a stress test – simulating an average phone on a slow 3G/4G/5G connection with heavy CPU throttling.
Out of the gate this means your mobile score is always under tougher conditions. Google does this intentionally to reflect how real users on older phones or patchy mobile networks might experience your site.
Why is my mobile score so unpredictable?
Through our experiences it is normal for the mobile score to fluctuate around dramatically. Here’s why:
- Harsher test conditions – Mobile tests emulate a mid-range device (like a Moto G4) on a slow connection. Any slight server hiccup, extra script, or big image can knock your score down fast.
- CPU & network bottlenecks – Mobile devices have weaker processors. Sites heavy on JavaScript or large images will always struggle more on mobile, where rendering takes longer.
- Real-World variability – PageSpeed Insights tests your site in real time. If your hosting infrastructure is a bit busy or any third-party infrastructure where content/scripts could be getting included from – your score changes too.
All of this means mobile scores are far more sensitive and volatile than desktop scores. Small changes – on your site or on the web in general – can cause big swings.
Meanwhile, desktop scores tend to remain more stable thanks to better processing power and faster connections.
What about Core Web Vitals?
Although it may look worrying, a fluctuating mobile score does not mean your website is broken. It is a sign to check whether your real users might have a frustrating experience on slower devices or weaker networks.
For example, have you tried visiting your website on your mobile whilst not connected to your super-fast home broadband. At Spindogs, we will always run a minimum of 5 stagged checks (preferably 10) and take an average score. One off tests don’t always tell the full story.
While a high PageSpeed Insights score is desirable, Google emphasises that passing the Core Web Vitals element of PageSpeed Insights as more critical for search engine rankings and reflective of a positive user experience. Core Web Vitals metrics measure real-world user experience and directly influence your website’s SEO performance.
Final thoughts
At Spindogs, we help our clients optimise for real-world usage – so your users get a fast, smooth experience, whether they’re on a laptop at home or a phone on the move.
Want to know how your site performs, and how to improve it?
Get in touch with our experts by completing the form below or, if you’re an existing client, reach out to our support team or your account manager.