Mobile visitors won’t wait. If a page loads slowly, they go back to the search results and click on a competitor — and you never find out they were there. The good news: most slow websites have a handful of clear causes that can be measured and fixed.
How to measure speed properly
Don’t rely on how it feels on your own computer and fast connection. Use the same tools Google uses:
- PageSpeed Insights — enter a URL and get two kinds of data: real-user data (if the site has enough traffic) and a lab test with a 0–100 score. Always look at the mobile result.
- Google Search Console — the “Core Web Vitals” report shows which groups of pages have problems, based on real users.
- Chrome DevTools (Lighthouse and Network) — for detailed analysis: what loads, how big it is and what blocks rendering.
Core Web Vitals in plain language
Google measures speed and experience with three metrics. A page “passes” when it is good for at least 75% of visits:
| Metric | What it measures | Good |
|---|---|---|
| LCP (Largest Contentful Paint) | When the largest element on screen appears — usually the main image or heading | up to 2.5 s |
| INP (Interaction to Next Paint) | How quickly the page responds to a click or tap | up to 200 ms |
| CLS (Cumulative Layout Shift) | How much content “jumps” while the page loads | up to 0.1 |
In plain terms: the page should show its main content quickly, respond to taps immediately and not move text under your finger while you read.
The ten most common causes
1. Oversized images
A 4–5 MB photo straight from the camera, displayed in a 400-pixel box, is the most common cause of a slow website. Fix: correctly sized images in a modern format (WebP or AVIF), several sizes for different screens, and lazy loading for images further down — except the main image at the top, which should load immediately.
2. Too many plugins and scripts
Every add-on — chat, pop-up, slider, visitor counter, social widgets — brings its own JavaScript. Individually small, together they slow the page down and especially hurt INP. Fix: list all scripts and remove those that bring no real benefit.
3. Heavy page builders and themes
Themes and page builders that “can do everything” load code for everything — including what your site never uses. Fix: a lighter theme, disabling unused modules or, for serious problems, a new site without that ballast.
4. A slow server (TTFB)
If the server responds slowly (the first byte arrives after more than 0.8 seconds), everything else is delayed. Causes include overloaded hosting, missing caching or slow database queries.
5. No caching or compression
Without proper caching the browser downloads the same files again on every visit. Without compression (gzip or Brotli) text files are several times larger than necessary.
6. Fonts
Several font families in many weights, loaded from external servers, delay text rendering and cause layout shifts. Fix: fewer variants, self-hosted fonts, font-display: swap and preloading the most important font.
7. Render-blocking CSS and JavaScript
If large files must be downloaded before anything is shown, the screen stays blank. Fix: less code, deferred scripts (defer) and removing unused CSS.
8. Third-party embeds
A YouTube video, Google Map or Facebook feed on the home page can download more data than the whole site. Fix: show a preview image and load the real embed only on click.
9. Sliders and big animations at the top
A slider with five large photos at the top slows down LCP, and usability research shows visitors rarely look beyond the first slide. One strong image and a clear message almost always work better.
10. Elements without reserved space
Images without set dimensions, banners and ads that appear later push content around — that’s CLS. Fix: give every media element a width and height (or aspect ratio) and reserve space for anything that loads later.
A speed-up plan: biggest impact first
- Measure the page on mobile in PageSpeed Insights and note LCP, INP and CLS.
- Optimise images — the biggest effect with the least risk.
- Remove unnecessary plugins, scripts and embeds.
- Enable caching and compression on the server.
- Sort out fonts and defer JavaScript that isn’t needed immediately.
- If TTFB is still high, consider better hosting or full-page caching.
- Measure again and compare with the starting point.
Tip
Don’t just test the home page. Measure your service and contact pages too — that’s exactly where visitors decide whether to get in touch.
When a new website is the better option
Optimisation has limits. If the site is built on a heavy page builder with dozens of plugins, it’s often cheaper and faster to build a new, lightweight site than to spend months patching the old one. Read the comparison in WordPress or a custom website.
If you want to know exactly why your website is slow and what is worth fixing, that’s a job for a technical audit: you get measured causes and a prioritised plan.
Engimotive · Published October 27, 2026