Your Core Web Vitals are quietly costing you enquiries

Most business owners find out about Core Web Vitals from an agency trying to sell them a rebuild. That is a shame, because the underlying idea is simple and worth understanding on its own terms: Google now measures how fast your site feels to real people on real phones, and uses it as a ranking signal.

Three numbers carry most of the weight. None of them are the "page load time" you might be used to.

The three measurements that matter

Largest Contentful Paint (LCP) is how long it takes for the biggest thing on screen — usually your hero image or headline — to appear. Google wants this under 2.5 seconds. It is the closest thing to "how long until this looks like a real page".

Interaction to Next Paint (INP) measures what happens when someone taps something. If your menu takes half a second to open, INP catches it. Under 200 milliseconds is the target.

Cumulative Layout Shift (CLS) is the one everybody has experienced without having a name for it: you go to tap a link, an advert loads above it, and you tap the wrong thing. Google scores that, and the target is under 0.1.

The important detail is that these are measured from actual visitors, not from a test run in a data centre. A site that scores well on a developer's laptop can still fail in the field.

What actually moves the numbers

In our experience the same handful of problems account for most poor scores, and none of them require a rebuild to fix.

• Unoptimised images. A 4 MB photograph straight off a camera, scaled down in the browser, is still a 4 MB download. Serving correctly sized AVIF or WebP usually halves the page weight on its own.
• Images without dimensions. If the browser does not know how tall an image will be, it cannot reserve the space, and everything below jumps when it arrives. That is your CLS score.
• Third-party scripts. Chat widgets, heat-map trackers, three separate analytics tags. Each one is a request to somebody else's server that your page waits on.
• Fonts loading late. Text that appears in one typeface and then re-renders in another is both a layout shift and a bad first impression. Pre-loading the font file fixes it.

How to check yours honestly

Run your own site through PageSpeed Insights and read the field data at the top, not the lab score below it. Field data is what Google actually uses. If there is not enough traffic to show field data, the lab score is a reasonable proxy — but throttle it to mobile, because that is where most of your visitors are.

A tip worth knowing: test a page that matters commercially, not just the homepage. Service pages and contact pages carry the enquiries, and they are often the ones nobody optimised.

Is it worth fixing?

Honestly, it depends. If you rank comfortably for your terms and your site loads in three seconds, this is a tuning exercise, not an emergency. If you are on page two for terms a faster competitor owns, it is one of the cheaper levers you have — performance work is measurable, and you can verify it yourself afterwards.

What we would push back on is being sold a full rebuild to fix a score. Most of the wins above are a day or two of work on an existing site. Ask for the before-and-after report.