In short: open PageSpeed Insights, paste in your website's address and look at the real-user data on mobile. Your website is doing fine if LCP is 2.5 seconds or less, INP is 200 milliseconds or less and CLS is 0.1 or less.
Minute 1: open PageSpeed Insights
Go to pagespeed.web.dev, paste in your website's address and click “Analyze”. It's a free tool from Google. Look at the Mobile tab first: that's where most people will see your website, and where everything is slower.
Minute 2: read the real-user data
At the top you'll see the real-user section: data from people who visited your website in Chrome over the last 28 days. What matters are three numbers, the Core Web Vitals:
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP | How long it takes for the main content of the page to show up (the photo or the big headline). | 2.5 s or less | over 4 s |
| INP | How long the page takes to respond when you tap a button or a menu. | 200 ms or less | over 500 ms |
| CLS | How much the page shifts around while it loads (that button that jumps just as you're about to tap it). | 0.1 or less | over 0.25 |
Google measures them at the 75th percentile: your website “passes” if at least three out of four visits get those good values. If all three are green, your website isn't slow, even if the score further down isn't 100.
Minute 3: if there's no real-user data
If your website doesn't get many visits, PageSpeed Insights will say there isn't enough data. In that case, look at the lower part, the diagnostics: it's a simulation (Lighthouse) on a slow phone. It helps you get your bearings, but it isn't what your customers actually experience. The simulation has no INP, because nobody interacts with the page; its stand-in is “Total Blocking Time”.
Minute 4: check Search Console
If you have Search Console, the Core Web Vitals report groups your pages into “Good”, “Needs improvement” and “Poor”, on mobile and desktop. It's the quickest way to tell whether the problem is one page or the whole website.
Minute 5: the real test
Grab your phone, turn off Wi-Fi, open an incognito window and go to your website. Count how long it takes to see the main content and try tapping the menu. If it drives you crazy, it drives your customers crazy.
What usually makes a website slow
- Huge images: 4 MB photos straight from the camera, not compressed or sized for the screen. This is the most common cause of a poor LCP.
- A heavy background video on the home page, with no lightweight placeholder image.
- Too many plugins and third-party scripts (chats, pixels, widgets) that block the page. They tend to make INP worse.
- Fonts and images with no reserved space, which make content jump as it loads. They make CLS worse.
- Slow hosting: if the server takes a while to respond, everything else arrives late.
The good news: almost all of this can be fixed without replacing your website. And if you do replace it, make sure the new one hits these three numbers from day one.