Website speed: why a slow site costs you money
You invest in ads. You pay for SEO. Traffic grows. But conversions? Flat. Or falling. And you wonder whether the problem is the offer, the price, or the ads.
The problem may be something you’d never think to check: your site is slow.
Not “a bit slow”. Slow enough that visitors leave before they see what you offer. Slow enough that Google ranks you below competitors. And slow enough that you lose customers every day without knowing it.
Speed isn’t a technical detail — it’s a business problem
Most site owners see speed as a technical matter that isn’t theirs. Something the developer handles. But site speed has a direct effect on the two things you care about most: how many people become customers and how many people find you through Google.
How speed affects conversions
Think about your own behaviour. You click a link and the page doesn’t load immediately — what do you do? Wait patiently? Or hit back and try the next result?
Most people do the second. Google’s data says 53 % of mobile users abandon a page that takes more than 3 seconds to load. More than half. And that’s just three seconds — an eternity on the web.
Now translate that into money. If you get 1,000 visitors a month and your site takes 5 seconds, hundreds of people never see your site at all. They never saw the offer, never read the testimonials, never filled in the form. They just left. And worse — they left for a competitor whose site loads faster.
How speed affects SEO
Since June 2021 Google has used Core Web Vitals as one of its ranking factors. Put simply: given two sites with comparable content and authority, the faster one ranks higher.
It isn’t the only factor — Google weighs hundreds. But it’s one you can influence. And unlike link building or content production, speed work shows results relatively quickly.
So a slow site costs you twice: once in lost conversions, and again in lower rankings. And those aren’t the only reasons a website doesn’t make money — speed is one factor, far from the only one.
What Core Web Vitals are and why they matter
Core Web Vitals are three metrics Google uses to measure how fast and pleasant your site feels to a visitor. You don’t need the technical detail — just what each measures and what the target is.
LCP — Largest Contentful Paint
What it measures: how fast the main visible content appears. Typically a large header image, a headline, or the whole hero block.
Target: under 2.5 seconds.
Why it matters: LCP is what a visitor perceives as “the page loaded”. If the main content only appears after 4 or 5 seconds, the user feels the site is broken — even if plenty has already loaded in the background.
Think of it as a shop window. If a customer arrives and sees empty space for 5 seconds, they turn around. They don’t care that everything is ready inside.
CLS — Cumulative Layout Shift
What it measures: how much the page shifts and jumps while loading. You know the feeling — you go to click a button, an image loads above it, the button jumps, and you click something else.
Target: under 0.1.
Why it matters: high CLS is one of the most irritating experiences on the web. The page looks loaded, then everything moves. The visitor loses trust — and trust is the basis of conversion. Nobody fills in a form on a site that behaves unpredictably.
The usual causes are images without defined dimensions and dynamically injected banners or widgets. The problem is especially critical on phones — and how customers actually see your site on mobile is something a desktop test will never show you.
INP — Interaction to Next Paint
What it measures: how fast the page responds when you click, tap or press a key. Specifically the time from your interaction to the moment the page updates visually.
Target: under 200 milliseconds.
Why it matters: INP replaced the older FID (First Input Delay) in March 2024 because it captures overall responsiveness better. FID measured only the first interaction; INP watches all of them and reports the worst.
When a visitor clicks “Add to cart” and nothing happens for half a second, they click again. The result: confusion, frustration, exit. The page has to respond immediately — 200 ms is where people stop perceiving a delay.
Core Web Vitals: targets at a glance
| Metric | What it measures | Target |
|---|---|---|
| LCP (Largest Contentful Paint) | How fast the main visible content appears | under 2.5 s |
| CLS (Cumulative Layout Shift) | How much the page shifts while loading | under 0.1 |
| INP (Interaction to Next Paint) | How fast the page responds to a click or tap | under 200 ms |
How to measure your own site
You don’t need to be a developer to find out where you stand. Free tools tell you everything essential.
PageSpeed Insights (start here)
Open PageSpeed Insights, enter your URL and click Analyze. A few seconds later you have a full picture.
What to look at:
- The 0–100 score — green (90+) is excellent, orange (50–89) needs attention, red (0–49) is a problem.
- Core Web Vitals — actual LCP, CLS and INP values from real user data (where available) and from a simulated test.
- Opportunities and Diagnostics — concrete recommendations.
Important: test the mobile and desktop versions separately. Mobile scores tend to be substantially worse because they simulate a slower connection and a weaker device. And mobile is where most of your visitors come from.
Lighthouse (a more detailed view)
Lighthouse is built into Google Chrome. Open DevTools (F12), go to the Lighthouse tab and run an audit. You get a detailed report covering not just speed but accessibility, SEO and more.
Lighthouse is useful mainly because it shows exactly which elements slow the page — including specific files and their sizes.
Chrome DevTools — the Network tab
For a more advanced look, open DevTools (F12) and go to Network. Reload the page (Ctrl+R) and watch. You’ll see every file being downloaded, how large it is and how long it takes.
This is where the surprises show up — a 5 MB background image, or a third-party script blocking rendering for 2 seconds.
The most common causes of slow sites
In audits, most speed problems fall into three categories. None are surprising, and nearly all are easy to solve.
1. Unoptimised images
By far the most common problem. Photos uploaded straight from a camera or a stock library at full resolution. A 4000×3000 pixel image displayed in an 800×600 space. A 3 MB PNG banner where a 200 KB WebP would do.
Images routinely make up 50–80 % of total page weight. Resize them and convert them to the right format, and you often solve most of your speed problem in one move.
2. Too many external scripts
Every tool you add to the site adds code that has to be downloaded and executed. Analytics, ad pixels, heatmaps, a chat widget, the cookie bar, remarketing scripts, conversion tracking…
Some sites carry 15 or 20 external scripts. Each needs to open a connection to a remote server, download code and run it. And because many load right at the start, they block the page content from appearing at all.
Plenty of them are unnecessary — tools somebody added two years ago that nobody uses now. Or three different analytics tools tracking the same thing.
3. Render-blocking resources
Some CSS and JavaScript files block rendering — the browser waits until they’re fully downloaded and processed before showing anything. If those files are large or slow, the visitor stares at a white page for seconds.
A typical case: the site loads a large CSS library (all of Bootstrap) and uses a fraction of it. Or three JavaScript files sit in the head that could easily wait until the page has rendered.
What you can do today (without a developer)
Some improvements need no technical knowledge at all. Simple steps you can take yourself — with a large effect on speed.
Convert images to WebP
WebP is a modern image format from Google offering 25–34 % smaller files than JPEG at comparable visual quality. An image that’s 500 KB as a JPEG lands around 350 KB as WebP — with no visible loss.
How:
- Use an online tool like Google’s Squoosh — drag the image in, download the WebP.
- Set quality around 80 % — you won’t see the difference from 100 %, but the file is far smaller.
- On WordPress, a plugin like ShortPixel or Imagify converts images automatically.
Turn on lazy loading
Lazy loading means images load only when the user scrolls to them. An image at the bottom of the page isn’t downloaded on load, only when the visitor needs to see it.
In practice that means adding loading="lazy" to images in the HTML. Most modern CMSs (WordPress, Webflow) have a single toggle for it.
Important: don’t lazy-load images above the fold — those you want as fast as possible, because the visitor sees them immediately.
Resize images to the size they’re displayed at
If an image displays at 800 pixels wide, there’s no point uploading it at 4000. The browser will scale it down, but it downloads all of it first.
Before uploading, resize to the maximum width it will be shown at. For most sites that’s 1200–1600 pixels. For thumbnails and smaller elements, 400–600 is usually plenty.
Audit your scripts
Open the site in Chrome, press F12 and look at the Network tab. Filter to JS. Go through the list and ask: do you really use all of these? Do you need three analytics tools? Is that chat widget — the one nobody has written to in a year — genuinely necessary?
Every removed script is less to download and a faster page.
Check your hosting
Sometimes the problem isn’t the site but the server. Cheap shared hosting can mean slow server response — and no front-end optimisation fixes that.
Check server response in PageSpeed Insights — TTFB (Time to First Byte) should be under 800 ms, ideally under 200 ms. If it’s much higher, consider upgrading.
When professional optimisation is worth it
The quick wins above you can do yourself, and they can move the needle a lot. But some situations call for a specialist.
Consider professional optimisation if:
- Your PageSpeed score is under 50 even after basic image work.
- The site runs on a custom system where you can’t easily change settings.
- You run a store with thousands of products, where optimisation is more complex.
- You need to deal with render-blocking resources, critical CSS or preloading — that takes technical knowledge.
- The site generates significant revenue, where every percentage point of conversion rate is real money.
In those cases speed work pays back fast. It isn’t cosmetic — it’s repairing a leaking funnel. What speed looks like alongside other conversion barriers in practice is in the Hotel Silva case study.
The takeaway
A slow site isn’t just an annoyance — it’s a specific financial loss. You pay to acquire visitors, and a slow site sends them away before they can look at what you offer.
Three things you can do today:
- Measure the site with PageSpeed Insights — 30 seconds.
- Optimise images — convert to WebP, resize, enable lazy loading.
- Audit your scripts — remove what you don’t use.
And if you want to know exactly what’s costing you customers — not just speed, but copy, UX and forms — that’s what Kaen watches continuously. Every problem comes with a concrete recommendation and a measurable hypothesis to verify it.