Website speed: how to get a Lighthouse score of 100

A slow website costs you customers you never hear about. Someone taps your link in a car park on one bar of signal, stares at a white screen, and goes back to Google for the next result. Good website speed fixes that, and a Lighthouse score of 100 is a handy way to know you've done the job properly.

This isn't theory. Here are three of my own sites, tested on 17 October 2026.

What Lighthouse actually measures

Lighthouse is Google's free testing tool. It scores a page out of 100 in four areas:

• PerformanceHow quickly the page loads and becomes usable.
• AccessibilityWhether people with disabilities can use it.
• Best practicesSecurity and modern web standards.
• SEOBasic technical things search engines need.

Lighthouse is a lab test: it loads your page in a simulated setting. Google also collects real-user data from Chrome, and that's where Core Web Vitals come in.

Core Web Vitals explained

Core Web Vitals are Google's measures of how a page feels to real people. There are three. Google calls a page "good" when it meets these thresholds at the 75th percentile of visits:

In plain English: show the main thing fast, react to taps quickly, and don't make the button move just as someone goes to press it.

How to test your website speed

1. Go to pagespeed.web.dev (PageSpeed Insights).
2. Paste in your page address and press Analyse.
3. Look at the Mobile tab first. That's how most local customers see you.
4. At the top, check the real-user Core Web Vitals section. If your site doesn't get enough traffic, Google may not have data, and that's normal for small sites.
5. Below that, look at the Lighthouse scores and the list of opportunities and diagnostics. That's your to-do list.
6. Test your home page, a service page and your contact page. They can score differently.
7. Run it a couple of times. Scores wobble a little between runs.

You can also run Lighthouse in Chrome: right-click, Inspect, then the Lighthouse tab.

Fix 1: images

Images are the usual culprit. A photo straight off a phone can be several megabytes. Shown at the width of a phone screen, it needs a fraction of that.

• Use WebP (or AVIF). Modern formats are much smaller than JPEG or PNG for the same quality.
• Size them properly. Don't load a 4000-pixel photo into a 600-pixel space. Export at the size it's shown, plus a larger version for sharp screens using srcset.
• Set width and height. Always add width and height to images so the browser reserves the space. This is the easy win for CLS.
• Lazy-load below the fold. Add loading="lazy" to images further down the page.
• Don't lazy-load the hero. The main image at the top is usually your LCP. Load it straight away, and consider fetchpriority="high".
• Ditch the slider. Carousels load several big images and lots of script for one that people actually see.

Fix 2: fonts

• Self-host your fonts. Serve them from your own site rather than a third-party service, to avoid extra connections.
• Use WOFF2. It's the smallest common font format.
• Use fewer weights. Regular and bold is usually enough. Every extra weight is another file.
• Use font-display: swap so text shows straight away in a fallback font.
• Preload the main font used above the fold.
• Or use system fonts. Zero download. Not as pretty, but very fast.

Fix 3: less JavaScript

JavaScript is what usually hurts INP and slows everything down. Most brochure websites need very little of it.

• Remove plugins you don't use. On WordPress, this alone can make a big difference.
• Question every third-party script: chat widgets, heatmaps, social feeds, multiple tracking tags. Each one costs speed.
• Load scripts with defer so they don't block the page.
• Avoid heavy page builders that add lots of code to every page.
• Embed videos and maps with a lightweight placeholder that loads the real thing on click.

Fix 4: caching, hosting and CSS

• Caching. Set long cache times for images, fonts, CSS and JavaScript so returning visitors don't download them again.
• Compression. Make sure your server uses Brotli or gzip.
• A CDN. Serving files from a network close to your visitors cuts the wait.
• Decent hosting. Cheap overloaded hosting makes the server slow to respond, and nothing else can fix that.
• Lean CSS. Remove unused styles and inline the small bit needed for the top of the page.

Getting the other three scores to 100

• Accessibility: good colour contrast, alt text on images, labels on form fields, proper heading order. My website accessibility guide goes through it.
• Best practices: HTTPS everywhere, no console errors, no outdated libraries.
• SEO: a page title and meta description, readable font sizes, crawlable links, a valid robots.txt.

The usual culprits on small business sites

When I test a slow small business site, it's nearly always one of these:

Work through it in this order

1. Fix images. Biggest win, least effort.
2. Remove scripts and plugins you don't need.
3. Sort fonts.
4. Turn on caching and compression.
5. Re-test in PageSpeed Insights and work through what's left on the list.

On a site built simply from the start, there's usually not much left to fix. That's why I build lean rather than bolting speed on afterwards.

Does a 100 score really matter?

Honestly, a 100 isn't magic, and Google doesn't rank pages purely on speed. Content, relevance and reputation matter more. But a fast, accessible site is better for every visitor, and it removes a reason for people to give up on you. Speed is one part of the bigger picture in my local SEO checklist.

Test like your customers browse

Lighthouse on mobile simulates a mid-range phone on a slower connection, which is far closer to real life than your office broadband. If your site feels fast on your laptop but scores badly on mobile, believe the mobile score. Also try your site on an older phone outside, on mobile data. Tap the menu, open the contact form, scroll a long page. If anything feels sticky or jumps about, that's what your customers feel too, and it's worth fixing even if the score already looks decent.

How I can help

Every £25-a-month website I build is made to be fast on phones from day one. If you want it taken to the same Lighthouse standard as the sites above, the SEO, speed and accessibility tune-up is £100, paid once. See everything on the pricing calculator.

Get my site to 100