Why fast websites convert better (and how to get there)

The brutal truth about website speed

Here's something most agencies won't tell you: your beautiful website is probably haemorrhaging money because it's too slow.

We've audited hundreds of sites over the years, and the pattern is depressingly consistent. Businesses spend £10k+ on gorgeous designs, then host them on bargain-bin servers with unoptimised images. The result? A 4-second load time that's silently killing conversions.

Amazon figured this out years ago. They found that every 100ms of added latency cost them 1% in sales. For a company doing billions, that's real money walking out the door.

But here's what's interesting: the same principle applies to smaller businesses. We've seen hotels increase bookings by 23% just by cutting load time from 3.5s to 1.2s. No redesign, no new copy, just speed.

What "fast" actually means in 2025

Forget everything you knew about speed metrics. Google's moved on, and so should you.

Core Web Vitals are the new baseline:

• •LCP (Largest Contentful Paint): Under 2.5 seconds. This is when your main content becomes visible.
• •INP (Interaction to Next Paint): Under 200ms. How quickly stuff happens when someone clicks.
• •CLS (Cumulative Layout Shift): Under 0.1. Those annoying jumps when images load late.

Miss these targets and Google will absolutely punish you in rankings. We've watched sites drop 20+ positions after a Core Web Vitals update because they ignored performance.

The real culprits (it's probably not what you think)

Everyone blames images. And yes, unoptimised images are a problem. But they're rarely the main issue.

The actual performance killers:

Third-party scripts are the silent murderer. That chat widget? 400kb of JavaScript. Analytics? Another 200kb. Heat mapping tool? 300kb more. Before you know it, you're loading 2MB of scripts before your actual content.

We recently audited a hotel website running 14 third-party scripts. Fourteen! The site took 8 seconds to become interactive. We stripped it down to 4 essential scripts and hit 1.8 seconds. Same functionality, 4x faster.

Render-blocking CSS is sneaky. Most themes load their entire stylesheet before showing anything. That's 200kb of CSS for a page that only uses 15kb of styles. Critical CSS extraction sounds boring, but it's often worth 500-800ms alone.

Web fonts are heavier than you'd expect. A single variable font can weigh 400kb. Multiply that by a few weights and styles, and you're looking at serious overhead. System font stacks aren't sexy, but they're instant.

The practical checklist

Right, enough theory. Here's what actually moves the needle:

Server-side wins (do these first)

1. Get on proper hosting. Shared hosting is fine for hobby projects. For business sites, you need either a quality managed host or edge deployment. We use Vercel for most projects—sites load from the nearest server to your visitor.

2. Enable HTTP/2 or HTTP/3. If your host doesn't support this by now, run. It allows parallel asset loading instead of the old queued approach.

3. Set up proper caching headers. Static assets should cache for a year. HTML should have short TTLs with revalidation. Most hosts get this wrong by default.

Image optimisation (the obvious stuff)

4. Use modern formats. WebP for photos, AVIF where supported. Both offer 30-50% smaller files than JPEG with identical quality.

5. Size images correctly. Don't serve a 2000px image to a 400px container. Use srcset and let the browser pick the right size.

6. Lazy load below-the-fold images. Native lazy loading is dead simple: just add loading="lazy" to your img tags.

JavaScript discipline (the hard part)

7. Audit every third-party script. Ask yourself: is this actually making us money? If not, kill it. Most sites can eliminate 3-5 scripts without losing anything important.

8. Defer non-critical JavaScript. Anything that isn't needed for initial render should load after the page is interactive.

9. Consider partial hydration. Frameworks like Next.js and Astro let you ship less JavaScript by only hydrating interactive components.

CSS cleanup

10. Extract critical CSS. Inline the styles needed for above-the-fold content, load the rest async. Tools like Critical make this straightforward.

11. Purge unused CSS. If you're using Tailwind, PurgeCSS is built in. For other frameworks, uncss works well.

The measurement routine

You can't improve what you don't measure. Here's our monitoring setup:

Weekly checks: - PageSpeed Insights on key pages - WebPageTest from multiple locations - Lighthouse CI in your deployment pipeline

Monthly deep dives: - Chrome DevTools Performance panel recording - Third-party script audit - Image compression review

Real user monitoring: - Google Search Console Core Web Vitals report - Analytics site speed reports

The key is consistency. One audit means nothing. Trends over time tell you if you're getting better or worse.

When to call in help

DIY performance optimisation works until it doesn't. Some situations genuinely need expert intervention:

• •Your TTFB is over 600ms despite good hosting
• •JavaScript execution time exceeds 3 seconds
• •You're stuck on legacy platforms that resist optimisation
• •Performance degraded and you can't identify why

We've done dozens of performance rescues for sites that hit a wall with self-service optimisation. Sometimes it's a quick fix (misconfigured CDN, bad caching rules). Sometimes it's a deeper architecture problem that needs surgical intervention.

The bottom line

Website speed isn't a nice-to-have anymore. Google's made it a ranking factor. Users expect instant everything. Your competition is probably faster than you.

The good news? Most performance issues have straightforward fixes. The bad news? They require discipline and ongoing attention.

Start with the server-side basics. Move to images. Then tackle JavaScript. Measure constantly. And don't let anyone tell you that a beautiful site has to be slow—that's just lazy engineering talking.

Your visitors (and your conversion rate) will thank you.