Why Your E-commerce Store Is Slow (And What It’s Really Costing You)

Slow page speed is one of the most common reasons why online stores’ marketing efforts fall flat. You might run ad campaigns with a budget that far exceeds your competitors’, but if users have to wait ages for your landing page to load, they will leave in a second. It’s simply impossible to maintain high conversion when the website’s performance is low. In this article, we'll break down exactly what the costs are and where the problem usually starts.

The numbers don't lie: low performance kills conversion

In 2020, Google commissioned Deloitte to conduct research to determine whether there was a real correlation between website performance and conversion rates in mobile retail. Dozens of brands – both small and large – from the U.S. and Europe were included in the study.

The final report was titled Milliseconds Make Millions – and it wasn’t an exaggeration. The researchers found that shaving 0.1 seconds off load time could boost conversion by up to 8.4% and increase average order value by 9.2%. It also made customers stay longer on the website, with the average number of pages viewed per session increasing by 5.2%.

To explain it a bit more clearly, let’s take a store generating $80,000 in monthly revenue, with a conversion rate of 2%. An 8.4% lift in conversions brings it to 2.17% – which, at the same traffic volume, translates to roughly $6,700 in additional monthly revenue. Add a 9.2% increase in average order value on top of that, and the total uplift climbs closer to $14,000 per month. And keep in mind that it’s just from a 0.1-second improvement in load time.

Slower websites don’t do well in Google’s search results

Low conversion is just the tip of the iceberg. Website performance has a significant impact on many aspects, including organic visibility in Google’s search results. In 2021, the company introduced Core Web Vitals – three metrics used to measure real-world page experience. It’s an integral part of its search engine’s algorithm. These metrics are pretty straightforward:

• LCP (Largest Contentful Paint) measures how long it takes for the main content of a page – the product image, the hero banner, whatever dominates the viewport – to load.
• INP (Interaction to Next Paint) measures how quickly your page responds to user interactions throughout their visit.
• CLS (Cumulative Layout Shift) tracks visual stability, for example, whether page elements jump around as it loads, pushing buttons out from under a user's finger mid-tap.

Google’s algorithm uses them as a tiebreaker of sorts – if two pages have comparable content quality and authority, the faster one should rank higher. However, there are also indirect consequences. Poor CWV scores almost always correlate with negative engagement signals, such as a high bounce rate, fewer pages viewed per session, etc. And these actively signal to Google that users don't find the website useful, which means it’s not worth displaying at the top of the results page. For many stores, that’s a death sentence. Why? According to experts at Smartbees software house, poor Core Web Vitals scores are, in most cases, baked into the website’s architecture from the beginning. It basically means it’s extremely difficult to improve without a complete overhaul.

The hidden tax on your paid campaigns

Something that many store owners don’t realize – at least at first – is the fact that their website’s performance affects the PPC ads’ price.

Here’s how it works: Google actively evaluates each ad’s quality based on three components – expected click-through rate, ad relevance, and landing page experience. Page speed is a huge part of the last one. If an ad has a low Quality Score, its cost-per-click rises. As a result, you have to bid higher just to maintain the same ad position as your competitors.

And how significant is this? Two years ago, one of Search Engine Land’s experts analyzed the performance metrics of his Google Ads campaigns. He compared ads rated above average and below average on Google’s Quality Score for relevance and landing page experience. The ones that scored well had, on average, their CPCs lower by 36% and the CTRs higher by 87%, which would have a massive impact on most e-commerce stores’ campaign results.

Why is your store slow? The usual suspects

So far, we've looked at what slow page speed might cost you. If those issues apply to your store, you need to find the bottleneck first. From Smartbees’ developers’ experience, most e-commerce websites that suffer from low performance are guilty of at least one of the following.

1. Plugin bloat – all e-commerce platforms, whether it’s WooCommerce, Shopify, or Magento, rely heavily on their vast third-party plugin libraries. That’s not a bad thing in itself, because the right modules enable developers to implement almost every feature imaginable. What’s important is that it’s much more efficient than coding everything from scratch. However, remember that every plugin you add to your store loads its own CSS/JavaScript files, which the browser must load. It increases the number of database queries required to render a single page. Additionally, some modules might be quite poorly optimized. If you have 20 or more plugins enabled, there’s a high chance they slow your store’s performance down.
2. Unoptimized assets and render-blocking resources – experts from the HTTP Archive estimate, as you can read in their Web Almanac report, that image files make up 42% of a website's average weight. The number is probably even higher for e-stores, for obvious reasons. And yet, many e-commerce sites still use heavy JPEGs or PNGs instead of modern formats like WebP or AVIF, which offer better compression without sacrificing quality. They also tend to upload raw, 5MB "hero" banners directly from a designer’s folder, serving them at the same suboptimal resolution for both desktop and mobile users, massively overloading the latter.

Yet, that’s only half the battle. Another culprit might be the lack of proper JavaScript optimization. Render-blocking scripts loaded synchronously in the page header force the browser to stop, download, and execute each file before it can render anything visible to the user. On a store with a dozen third-party integrations – Google Analytics 4, a chatbot, a review widget, an ad tracker, etc. – that queue can delay the first visible content by several seconds.

1. Hosting environments that can’t handle the traffic – unfortunately, many businesses still try to cut expenses by using shared hosting or an underpowered VPS. The problem is, e-commerce platforms are inherently resource-intensive. Even if your store performs adequately at low traffic volumes, it might begin to crack during a seasonal sale right before Christmas or just after you decide to widen your product range, massively expanding your database.

As you can conclude by now, all these issues usually get worse as the business grows. That is exactly why you should address them as soon as possible, preferably from the moment you start building your store from the ground up. The only way to prevent further performance issues is to act right away.

The single most important decision at that point will be choosing the right e-commerce platform. If you’re planning on serious growth, you should definitely consider Magento 2 among all the options. It’s one of the most scalable systems – its architecture is built to handle high traffic volumes, large product catalogs, complex pricing logic, and integrations with ERP and warehouse systems by design, without the performance ceiling that limits many off-the-shelf SaaS solutions. 

But like any enterprise-grade platform, it delivers on that promise only when it's configured correctly from the start. And this is where having the right technical partner who knows the platform inside out matters. The specialists at Smartbees have helped merchants build and maintain Magento 2 stores at enterprise scale. If you want to know more, check out Smartbees' case studies and see for yourself how they approached the issues discussed above.

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