Lighthouse scores vs real-user Core Web Vitals: which one counts?
Why your Lighthouse performance score and Google's Core Web Vitals often disagree, and how to use both to make a site faster.
You run Lighthouse and get 61. Search Console says your Core Web Vitals pass. Or the other way round. Both are right — they measure different things.
Lighthouse is a lab test
Lighthouse loads one page once, on a simulated mid-range phone with a slow network, and scores it from 0 to 100. It’s repeatable, so it’s good for finding causes: render-blocking CSS, oversized images, unused JavaScript, slow server responses. Each failed check comes with an estimate of the time fixing it would save.
Scores: 90 and above is good, 50–89 needs work, below 50 is poor.
Core Web Vitals come from real visitors
Google’s Core Web Vitals come from the Chrome UX Report: how the page actually behaved for real Chrome users over the last 28 days, at the 75th percentile.
- LCP (Largest Contentful Paint): how long until the main content shows. Good: 2.5 s or less.
- INP (Interaction to Next Paint): how quickly the page responds to taps and clicks. Good: 200 ms or less.
- CLS (Cumulative Layout Shift): how much the layout jumps around. Good: 0.1 or less.
These are what Google uses for page experience. A small site may not have enough Chrome visitors for Google to publish them; then the lab test is your best guide.
Why they disagree
Your visitors may have faster phones and networks than Lighthouse’s simulated device — or slower ones. Real users also scroll, click and return to cached pages, which a single lab run doesn’t.
How to use both
- Check real-user data first. If LCP, INP or CLS is poor, that’s what to fix.
- Use Lighthouse to find why. Start with the failed checks that save the most time.
- Test one page per template. Twenty blog posts built from the same template share the same problems — test one blog post, one product page, one service page.
- Re-measure the same pages. Compare like with like, or a score will move just because a different page was tested.
Abstrora does this in every audit with Lighthouse turned on: mobile and desktop scores for one page per template, every failed check with its estimated saving, and real-visitor Core Web Vitals where Google has them.
