Website Speed and Core Web Vitals: How Many Customers a Slow Website Costs You

Every extra second of loading means fewer enquiries and more expensive ads. I explain what Core Web Vitals are, how to test your website in 2 minutes and what helps the most.

Most people now open websites on their phones, often on a slower connection. If a page takes longer than 3 seconds to load, many of them leave before they even see what you offer. A slow website doesn't just lose visitors – it loses ad money too. You paid for the click, but the customer closed the page.

What are Core Web Vitals

Core Web Vitals are three measurements Google uses to judge how pleasant a website is to use. They are among the signals Google takes into account when ranking search results.

• LCP (Largest Contentful Paint) – how quickly the main content appears. Good is under 2.5 seconds.
• INP (Interaction to Next Paint) – how quickly the page responds to a click or tap. Good is under 200 milliseconds.
• CLS (Cumulative Layout Shift) – whether content “jumps” while loading. Good is under 0.1.

How to test your website in 2 minutes

1. Open PageSpeed Insights (pagespeed.web.dev) and enter your website address.
2. Look at the mobile result – it matters more than desktop.
3. If your website has enough traffic, you'll also see data from real users at the top. Those are the numbers Google goes by.
4. Below you'll find specific recommendations sorted by how much time they save.

The most common causes of a slow website

• large images – a phone photo can be 5 MB, a website needs 150–300 kB
• too many plugins and third-party scripts
• a heavy theme with effects nobody needs
• cheap or overloaded hosting
• no caching
• content that loads late and pushes the page around – for example a banner without reserved space

What helps the most

• Images converted to WebP and resized to the size they're actually displayed at.
• Lazy loading for images that aren't visible right away.
• Fewer plugins – switch off every one you don't need.
• Good hosting with caching turned on.
• Reserved space for images and banners so content doesn't jump.
• Fonts hosted on your own server, only in the weights you really use.

Speed and advertising

Page speed affects your campaigns too. When rating a landing page, Google Ads also considers the experience it offers – a slow page can lower your Quality Score and make clicks more expensive. With Meta ads, many people leave before the page even loads – in your stats you'll see it as the gap between link clicks and landing page views.

A real example

My own website, ambidesign.eu, scores 97–100 on mobile and desktop in Lighthouse tests (the tool PageSpeed Insights is based on). It's not magic: lightweight code without unnecessary plugins, WebP images, self-hosted fonts and no jumping content.

To find out what else may be holding your website back on Google, read Website SEO audit: 10 mistakes.

Want to know how fast your website is and what I'd improve first? Send me the address through a free audit – within 48 hours you'll get specific recommendations.