How half a second of load time costs you 7% revenue

Speed is an underrated part of website management. Not because it is hard to explain, but because the impact only shows once you start measuring. Google research shows that every half second of extra load time on mobile traffic costs about 7% in conversion. For an SMB webshop doing ten thousand euros a month, that is nearly eight hundred euros lost monthly. Per half second.

What I check first for every new client

Three steps, in order of impact, all achievable within one week.

1. Shrink images and lazy-load

In nine out of ten cases this is the biggest issue. Hero photos of four megabytes, product images that were never optimised, screenshots in original resolution. It is baked into how content is delivered.

What we do:

• Convert to WebP format (smaller than JPEG, better quality than PNG).
• Multiple resolutions per image (mobile does not get a 1920px photo).
• Below-the-fold images load only when they scroll into view.

Impact: 40-60% faster page load on average, with no loss in quality.

2. Bundle and defer JavaScript

Tracking scripts, chat widgets, cookie banners, marketing tags. Individually small, together they can delay first interaction by two to three seconds.

What helps:

• Marketing scripts load only after first paint.
• Chat widget initialises after four seconds or on scroll.
• Cookie banner immediate, but without an external library.

3. Inline above-the-fold CSS

This is more technical but enormously effective. The CSS needed for what you immediately see (header, hero) gets inlined into the HTML. The rest loads asynchronously. The difference: visitors see something straight away, even on slower connections.

Rule of thumb: max 14 kilobytes of critical CSS. That fits in the first network packet and arrives together with the HTML.

What you do not need to do

Some optimisations sound impressive but barely move the needle:

• Upgrading the server when the site already runs on modern shared hosting. The bottleneck is rarely the server, almost always the assets.
• Migrating to a different CMS for speed alone. A well-maintained WordPress or Statamic can be fast; a poorly maintained custom site is always slow.
• Stacking caching plugins. One properly configured layer is plenty. Multiple layers create conflicts.

How to measure

Three tools I use daily:

• PageSpeed Insights (Google). Gives Core Web Vitals: LCP (speed of main element), CLS (does the layout jump?), INP (responsive on interaction?). This is what Google also factors into ranking.
• WebPageTest.org. Shows a video of how your site loads from various locations. Visually handy to convince colleagues or clients.
• Cloudflare Web Analytics. Free, no cookies, gives real-user metrics across all visitors.

Don't do everything at once. Start measuring on one page (homepage), change one thing, measure again. Keep a log so you know in six months what worked and what didn't.

When to bring someone in

If your website delivers more than fifty leads or customers per month and the PageSpeed Insights score is below 70 on mobile, an optimisation engagement pays for itself within three months. If your site is purely a business card, a quick DIY check is often enough.

Also read

• New website, same approach: relaunched online - how I apply these principles to my own site
• What AI really means for your SMB - process automation with AI, practical examples

Want to know what is specific to your site? I do a free short audit and send you an email with the three highest-impact improvements. No sales pitch.