Site Speed and Conversion: Every Second Costs You Money

Website speed isn't a technical luxury — it's a direct revenue question. Google's own research shows that a large share of mobile visitors abandon a site if it takes more than three seconds to load, and every additional second makes the ratio worse. The good news is that speed mostly comes down to a few well-understood factors, and most of them can be fixed in a day or two. This article looks at how much a slow site actually costs you, the four biggest slowdowns, what order to fix them in, and how to stay fast over the long term.

How much are you losing on a slow site?

More than you'd think — and the loss scales with your traffic. Large e-commerce players have long published that load time and conversion are tightly linked: a few hundred milliseconds of slowdown causes a measurable drop in sales. Take a simple, conservative example. Say a shop gets 10,000 monthly visitors, converts at 2%, and has an average order value of 50,000 HUF. That's 200 orders a month, 10 million HUF in revenue. If slow loading drives away even 10% of visitors before the page becomes usable, that's 20 lost orders a month — one million forints, every single month, purely because of speed. That's the number that makes performance a "now" task rather than a "someday" one.

The four biggest slowdowns

On the vast majority of slow sites, the same four things are responsible. Start here before reaching for anything more complex.

• Images. On a typical page, images are the larger part of what gets downloaded. A single unoptimized, several-thousand-pixel-wide photo can weigh several megabytes on its own. A modern format (WebP or AVIF), a resolution matched to the display size, and lazy loading together cut image weight dramatically — often by 70–80% — with no visible quality loss.
• JavaScript. Every script that runs occupies the browser's main thread and delays the point at which the page becomes usable. Analytics, a chat widget, a heatmap, social embeds: harmless individually, but together they add megabytes of code and seconds to the load. The question is always: do you actually use all of it?
• Fonts. Several custom web fonts, each in several weights, quickly add up to hundreds of kilobytes. Worse, with the wrong setting the text stays invisible until the font finishes downloading. Load only what you truly use, and set font-display: swap so text is readable immediately.
• Hosting. Server response time (TTFB, Time to First Byte) is how long it takes for the first byte to arrive. Under 200 ms is good; above that the delay is noticeable. A modern edge host — such as Vercel or Cloudflare — usually delivers this out of the box, with no hardware investment.

Quick wins — in the right order

The order matters. The highest-return steps, in sequence:

1. Optimize images. Typically half a day to a day of work, and on its own the biggest, most immediately noticeable speed-up. Start here.
2. Remove unnecessary JavaScript. Look at what you actually use. Removing long-forgotten scripts often frees up hundreds of kilobytes and valuable seconds.
3. Fix server response time. If you're not on edge hosting, moving to a modern platform is often the single biggest one-time TTFB gain.
4. Trim fonts. One or two families instead of five, only the weights you use — another few hundred milliseconds back.

How to stay fast long term

Speed isn't a one-time fix; it's a state you maintain. A new plugin, a bigger image, a seasonal campaign page can slow down what you once put right. So measure it: a regular — even weekly — check with Google Lighthouse or Core Web Vitals reveals regressions before your visitors notice. This can be automated too, with a scheduled measurement that alerts you when performance drops below a threshold. We wrote in detail about the specific metrics — LCP, INP, CLS — and which to fix first in our Core Web Vitals article. And if you'd rather not deal with any of this, we design every Dexuro project with a performance budget from the start, and our services include speed audits of existing sites — get in touch and we'll show you where you're currently losing time and customers.