What Are Core Web Vitals?
Core Web Vitals are three specific metrics that Google uses to measure how good your website feels to use. Since June 2021, these metrics directly affect where your site shows up in Google search results.
Think of it this way: Google doesn't just care about what your website says — it cares about how your website behaves. Is it fast? Is it stable? Can users interact with it without frustration?
Core Web Vitals answer these three questions with three metrics:
- LCP — How fast does the main content appear?
- INP — How quickly does the page respond when you click something?
- CLS — Does stuff jump around as the page loads?
Let's break each one down in plain English.
LCP: Largest Contentful Paint
What it measures
How long it takes for the biggest visible element on your page to show up. This is usually your hero image, your main headline, or a large video thumbnail.
Why it matters
This is the moment when a user goes from "waiting" to "reading." It's what most people mean when they say a site "loaded." Everything before LCP is a blank screen or a partial page — neither inspires confidence.
What "good" looks like
| Rating | LCP Time |
|---|---|
| Good | Under 2.5 seconds |
| Needs Improvement | 2.5 – 4.0 seconds |
| Poor | Over 4.0 seconds |
Common causes of bad LCP
- Giant hero images — A 3MB PNG that should be a 200KB WebP
- Slow server response — The server takes too long before it even starts sending the page
- Render-blocking JavaScript — Scripts that prevent the browser from showing content
- Unoptimized fonts — Custom fonts that block text from appearing until they download
How to think about it as a founder
Imagine walking into a store and the lights don't turn on for 4 seconds. That's what a bad LCP feels like. You'd walk out. Your users do the same thing.
INP: Interaction to Next Paint
What it measures
How quickly your page responds after someone clicks a button, taps a link, or types in a field. Specifically, it measures the delay between the user's action and the visual response.
Why it matters
If someone clicks "Sign Up" and nothing visibly happens for 500 milliseconds, they'll click again. And again. This creates frustration, duplicate submissions, and the feeling that your product is broken.
What "good" looks like
| Rating | INP Time |
|---|---|
| Good | Under 200ms |
| Needs Improvement | 200 – 500ms |
| Poor | Over 500ms |
Common causes of bad INP
- Heavy JavaScript execution — Complex animations, data processing, or poorly optimized code running in the background
- Too many event listeners — Every click triggers a cascade of operations
- Third-party scripts — Chat widgets and analytics tools competing for the browser's attention
How to think about it as a founder
You know that frustrating feeling when you press an elevator button and nothing lights up? You press it again, harder. That's bad INP. A good website responds to every action instantly — even if the full result takes a moment.
CLS: Cumulative Layout Shift
What it measures
How much the content on your page moves around unexpectedly as it loads. Images popping in and pushing text down, buttons shifting position, banners appearing and shoving content out of the way.
Why it matters
This is arguably the most frustrating user experience issue. You're about to click "Start Free Trial" and suddenly an image loads, the button jumps down, and you accidentally click an ad instead. Every user has experienced this — and they hate it.
What "good" looks like
| Rating | CLS Score |
|---|---|
| Good | Under 0.1 |
| Needs Improvement | 0.1 – 0.25 |
| Poor | Over 0.25 |
Common causes of bad CLS
- Images without dimensions — The browser doesn't know how tall an image is until it loads, so content shifts when it appears
- Ads or embeds that load late — Third-party content that pushes your own content around
- Fonts that swap in — When a web font replaces the fallback font, text can change size and shift everything
- Dynamic content injection — Banners, cookie notices, or alerts that push content down after the page has already rendered
How to think about it as a founder
Imagine reading a newspaper, and every few seconds someone grabs the page and shifts it 2 inches to the left. That's what bad CLS feels like on a website.
How Google Uses These Metrics
Google collects Core Web Vitals data from real Chrome users (through the Chrome User Experience Report) and uses it as a ranking signal. Here's how it works:
- When Chrome users visit your site, their browser quietly records LCP, INP, and CLS values
- Google aggregates this data over 28 days
- Your site gets classified as having "good," "needs improvement," or "poor" Core Web Vitals
- This classification affects your search rankings — not as the #1 factor, but as a tiebreaker
In competitive SaaS markets, where you and five competitors have similar content and authority, Core Web Vitals can be the difference between page 1 and page 2.
How to Check Your Core Web Vitals
Three easy ways:
-
PageSpeed Insights — Go to pagespeed.web.dev and paste your URL. You'll see all three metrics with pass/fail indicators.
-
My free checker — Use my PageSpeed checker for a cleaner view of your scores.
-
Google Search Console — If you have Search Console set up, go to "Core Web Vitals" in the left sidebar. This shows real user data, not just lab tests.
What to Do If Your Scores Are Bad
Don't panic. Bad Core Web Vitals are fixable. Here's the priority order:
Fix LCP first (biggest impact)
- Optimize your hero image (convert to WebP, compress, set dimensions)
- Remove render-blocking scripts
- Use a CDN if you're not already
Fix CLS second (most annoying to users)
- Add width and height attributes to all images
- Reserve space for ads and embeds
- Use
font-display: swapfor web fonts
Fix INP third (most technical)
- Reduce JavaScript bundle size
- Defer non-essential scripts
- Break up long tasks into smaller chunks
If this sounds overwhelming, that's what I do. I build and optimize SaaS frontends specifically for performance. Check your score and reach out if you want help fixing it.
FAQ
Do Core Web Vitals really affect my Google ranking?
Yes, since June 2021. Google has confirmed that Core Web Vitals are a ranking signal. They won't single-handedly make or break your rankings, but in competitive niches, they serve as a tiebreaker between sites with similar content quality.
How long does it take for improved Core Web Vitals to affect rankings?
Google re-evaluates your Core Web Vitals over a 28-day rolling window. After you fix performance issues, expect 4-8 weeks before you see ranking improvements, as Google needs to collect fresh data from real users.
Can I pass Core Web Vitals on Webflow or WordPress?
It's possible but difficult. Both platforms add overhead that makes it harder to achieve good scores. Many SaaS founders who start on Webflow eventually move to custom code when performance becomes a priority.
