Why you should improve Core Web Vitals in WordPress

The test that reveals if your visitors are leaving your website

When a user clicks through to your website, it is immediately assessed. The page needs to load quickly, behave stably and respond without delay. If it doesn't, you lose momentum from the first second.

Poor user experience is a major barrier to conversion

Even a strong message loses impact if navigation feels slow or content moves while the page loads. Every time the user encounters unnecessary friction, the likelihood of the visit being cancelled increases.

It's also about trust. A technically weak website can make the company behind it look less professional. The user experience is therefore not only a question of functionality, but also of credibility.

Speed isn't just about seconds, it's about results

Small delays may seem insignificant. They aren't. When the most important content is displayed too late, more users drop out before they get to the next step. This is especially true on pages where you want the user to contact you, sign up or buy something.

This is where performance becomes practical: you get less out of the traffic you've already attracted.

The numbers Google uses to rate your website

Core Web Vitals consists of three specific metrics: LCP, CLS and INP. Together, they measure how quickly the page displays its most important content, how stable the layout is and how quickly the page responds to user actions.

LCP measures when the most important content becomes visible

LCP stands for Largest Contentful Paint. The metric shows how long it takes for the largest visible element on the page to load. This is often a top image, a hero section or a large headline.

Google's yardstick for LCP:

• 0-2.5 seconds = God (Green)
• 2.5-4 seconds = Needs improvement (Yellow)
• Over 4 seconds = Bad (Red)

Google recommends that the LCP should be no more than 2.5 seconds. If it is higher, the page is perceived as slow. The user doesn't see the content that confirms that the page is relevant fast enough.

What affects LCP the most:

• Database queries in WordPress that slow down the server
• Server response time (TTFB - Time to First Byte)
• Render-blocking JavaScript and CSS
• Image size and format
• Fonts that block rendering

CLS measures if the layout jumps around

CLS stands for Cumulative Layout Shift. It measures how much content moves while the page is loading. This is what happens when a button moves just before the user clicks or when text is pushed down by an image that loads too late.

Google's benchmark for CLS:

• 0-0,1 = God (Green)
• 0,1-0,25 = Needs improvement (Yellow)
• Over 0.25 = Bad (Red)

A good CLS score is 0.1 or lower. High CLS creates error clicks, uncertainty and a feeling that the site is not technically under control.

What causes high CLS:

• Elements added to the DOM without reserving space
• Images and videos without specified size (width/height)
• Fonts that load late
• Adverts and embedded content that load dynamically
• Animations without the will-change CSS property

INP measures how quickly the page responds to user input

NP stands for Interaction to Next Paint. It measures how quickly the page responds when the user clicks, taps or interacts with an element. If it takes too long, the page feels heavy even though it looks fully loaded.

Google's yardstick for INP:

• 0-200 milliseconds = God (Green)
• 200-500 milliseconds = Needs improvement (Yellow)
• Over 500 milliseconds = Bad (Red)

Google recommends an INP of no more than 200 milliseconds. Poor INP is often caused by heavy JavaScript, too many scripts or components blocking the browser.

What does INP affect:

• Too many event listeners to process
• Heavy JavaScript that needs to be parsed and executed
• Main thread blocking (when the browser is busy with too much work)
• Third-party scripts (ads, analytics, chat widgets)
• Complex DOM manipulations

Mobile-friendliness is a basic requirement

Core Web Vitals shouldn't just look pretty on desktop. They need to work in real-world conditions on mobile. That's where technical issues often become most apparent.

A heavy theme, large images and many scripts hit the mobile user the hardest. Therefore, performance must be assessed based on the experience the user actually has on a regular smartphone.

Important context: Google user mobile-first indexing, which means that the mobile version of your website is ranked first in search results. A poor mobile experience therefore directly affects your search rankings.

The consequences of ignoring technical issues

It can be tempting to de-prioritise technical improvements, especially if your website looks well-functioning at first glance. But the problems quickly show up in the data: lower engagement, more bounces and less impact from the traffic you've already generated.

Better technology gives competitors an advantage

When multiple websites compete for visibility in search results, overall quality becomes important. If the content is roughly equally strong, the technically best performing website will have an advantage.

Core Web Vitals don't determine rankings alone. But a weak technical experience makes it harder to compete.

Typical challenges with Core Web Vitals in WordPress

WordPress is a powerful platform, but it makes demands on the technical structure. Many performance issues are not caused by the system itself, but by the choices made along the way.

Heavy themes and too many plugins load the site

A common problem is large default themes with features you never use. They add unnecessary code that the browser still has to fetch and process.

The most important thing is not theme size, but theme quality. A well-structured theme with 50 KB of code can have much better performance than a poor theme of 150 KB. The problem is:

• Poorly written CSS that is not optimised
• JavaScript that runs for no reason
• Too many hooks and filters that slow down the page
• Lack of critical CSS implementation

When combined with many plugins, the solution quickly becomes heavy. The result is longer loading time, more complex debugging and poorer stability.

A rule of thumb: Each plugin should have a specific purpose. A plugin that is only used on one page can often be integrated directly into the page instead.

Unoptimised images create unnecessary load

Images are one of the most common causes of slow pages. If they are uploaded without compression or in file formats that are too heavy, the amount of data increases significantly. This especially affects mobile users.

Specific image issues:

• Images without specified width/height (causes CLS)
• Missing srcset for responsive images
• Old file formats (JPG) instead of modern formats (WebP, AVIF)
• Images that are not lazy-loaded
• Images loading without lazy loading attribute even though they are below the fold

Here the benefits are often clear. Properly customised images improve both LCP and the overall experience without changing the content of the page.

The database as an often ignored performance bottleneck

A poorly optimised WordPress database can be just as problematic as bad images, but it's rarely mentioned.

Database issues especially affect:

• TTFB (Time to First Byte) - the server is slower to respond
• Revision stack collection (WordPress stores 20+ revisions per page by default)
• Autoloaded options that are too big
• Too many database queries on each page view
• No caching of database results

How to optimise the WordPress database:

• Limit revisions: define('WP_POST_REVISIONS', 3);
• Rydop autoloaded options (many plugins put too much data here)
• Use database caching (Redis or Memcached)
• Install a WordPress database optimisation plugin
• Regular maintenance (table defragmentation)

Render-blocking resources block the entire page

This is often the main reason for poor LCP. If CSS and JavaScript need to be parsed before the page can be displayed, the user waits unnecessarily long.

What blocks rendering:

• CSS i . without critical CSS implementation
• JavaScript in . without defer or async
• Third-party scripts (ads, analytics) that must run before the page is displayed
• Fonts that load without font display strategy

Fonts can significantly slow down LCP

Many websites wait for Google Fonts (or other web fonts) to load before displaying text. This can delay LCP by 500+ milliseconds.

Font optimisation:

• Bridge font-display: swap; to display the fallback font immediately
• Preload important fonts: <link rel="preload" as="font" href="font.woff2" />
• Limit font variants (if you use 12 variants, it's too much)
• Self-hosted fonts instead of external loader

Hosting and server response sets the technical framework

A slow server makes the entire website slow. But nuance is important here.

Server response (TTFB) affects LCP, But it's not just about “expensive premium hosting”. It's about:

Factors affecting TTFB:

• PHP version: PHP 8.0+ is significantly faster than PHP 7.4
• Database optimisation: Bad queries can double TTFB
• Caching strategy: Object caching (Redis, Memcached) is more important than hosting choice
• Server location: If the server's geographic location is far from the user, TTFB is increased
• Load on the server: Shared hosting can become congested during peak hours

A WordPress hosting without server-side caching and with PHP 7.2 will be slow - regardless of price.

Honest insights into working with optimisation

When discovering technical issues, it's tempting to look for a quick fix. But Core Web Vitals are rarely permanently improved with a single plugin or a superficial tweak.

Plugins and automated solutions don't solve everything

Plugins for caching, minification and image compression can improve performance. These are useful tools. But they don't solve problems stemming from heavy code, poor structure or an overloaded theme.

If the cause lies in the structure itself, adding another layer of optimisation on top won't help. The problem needs to be solved at the source.

Some improvements require technical intervention

Significant improvements often require work on code structure, scripts, fonts and the order in which content is loaded. This is where the big wins lie.

It doesn't necessarily require a completely new website. But it does require technical insight, prioritisation and a clear understanding of what's actually slowing down the site.

How to get started improving your WordPress website

Working with Core Web Vitals should start with data. Not with guesses. Only when you know which pages and elements are causing problems can you prioritise correctly.

Measure the current problems before you change anything

Use relevant analytics tools to measure how the website performs with real users. Look at specific pages. Look at mobile. Look at what elements affect LCP, CLS and INP.

It provides a useful basis for decision-making. Without it, you risk spending time treating symptoms.

Prioritise the changes that will have the most impact

You don't have to fix everything at once. Start with the errors that affect the most important pages and the most important metrics. Is it the images that are dragging down LCP? Is it scripts breaking INP? Is it missing sizes of media and components creating CLS?

This approach provides faster results and more realistic optimisation work. First, overview. Then prioritisation. Then improvement.

Is your website technically ready?

Core Web Vitals in WordPress is ultimately about something simple: Can your website deliver a fast, stable and trustworthy experience when someone visits it?

If the answer is no, it's worth investigating where the problems occur and what can realistically be improved. Sometimes a few technical tweaks are enough. Other times, it requires a more fundamental clean-up in the theme, plugins or hosting environment.

If you want a professional assessment of how your website is performing, it can be useful to get an external view of the solution. It makes it easier to distinguish between small errors that can be fixed quickly and more fundamental issues that require more effort.

At Siite, we help companies identify technical bottlenecks in WordPress and prioritise the improvements that make the most sense in practice. If you would like a no-obligation review, feel free to contact us.