Why website speed is a marketing problem

You can have the best ad, the sharpest offer and exactly the right audience. If the page they land on takes too long to load, many of them leave before they ever see it.

Speed feels like a technical detail, but it’s one of the cheapest ways to get more from the marketing you already pay for: every visitor you keep is one you don’t have to buy again. Here’s what the research says, how to measure your own site, and the fixes that make the biggest difference.

What the research says

The most quoted study, Milliseconds Make Millions, was carried out by Deloitte and 55 for Google. It followed 37 European and American brands across more than 30 million sessions and found that a 0.1-second improvement in mobile load time raised retail conversion rates by 8.4% and travel conversion rates by 10.1%. Retail shoppers also spent 9.2% more.

Portent’s analysis of more than 100 million page views across 20 websites found that a B2B site loading in one second converts three times better than one loading in five seconds, and five times better than one loading in ten. For online shops, a one-second page converted 2.5 times better than a five-second page.

Individual businesses report the same pattern. Google collects their results on web.dev:

Why slow pages cost more in advertising

Speed affects what you pay for traffic as well as what it returns. Google Ads gives each keyword a Quality Score built from three parts: expected click-through rate, ad relevance and landing page experience, which Google describes as how relevant and useful your landing page is to people who click your ad. A slow, frustrating page drags that score down, which can raise your cost per click and lower where your ads appear.

On social platforms the leak is even simpler: people who click an ad and then wait often never arrive, and you pay for the click either way. The same applies to email: a newsletter that links to a slow page loses readers at the moment they were most interested. That’s why we treat a landing page’s speed as part of the campaign, not an IT job for later.

The three numbers that matter

Google measures real-world page experience with three Core Web Vitals. A page passes when at least 75% of real visits are “good” on all three:

The bar isn’t as high as it sounds, yet most websites miss it. The HTTP Archive’s 2025 Web Almanac found that only 48% of websites pass all three on mobile, and 56% on desktop. Loading speed is the most common failure: just 62% of sites have a good LCP on mobile.

How to check your site in ten minutes

Start with free tools, then test like a customer:

Lab tests simulate a mid-range phone on a slow connection, so scores can vary between runs. Field data, collected from real Chrome users over the previous 28 days, is what Google uses to judge page experience. Then do the most honest test of all: open your site on a mid-range phone using mobile data.

What usually slows sites down

• Huge images. A 4 MB photo straight from a camera or stock library is one of the most common problems we see. Modern formats help: Google reports that WebP images are typically 25–34% smaller than comparable JPEGs, and AVIF is often smaller still.
• Third-party scripts. Chat widgets, pop-ups, heatmaps, social feeds and several tracking tags each add weight and compete for the phone’s processor.
• Heavy themes and page builders that load code for features you don’t use.
• Web fonts loaded from other servers in many weights.
• Slow hosting without caching, which delays everything else.
• Animation that starts too early. Even decorative motion can hold a page up on a mid-range phone. Start it once the content has loaded.

Fixes, in order of impact

1. Resize and compress images. Serve WebP or AVIF, use srcset so phones get smaller files, and give every image a width and height so the layout doesn’t jump.
2. Remove the scripts you don’t need. For each plugin and tag, ask whether it earns its place. Load the rest after the main content, and only after consent where the law requires it.
3. Prioritise the main image. Give your hero image fetchpriority="high", and lazy-load images and videos further down the page.
4. Host your fonts yourself and load only the weights you use.
5. Turn on caching and a CDN, so repeat and distant visitors get pages faster.
6. Make the next page instant. Chrome’s Speculation Rules can prepare the next page when someone hovers over a link, and keeping pages eligible for the back/forward cache makes the back button instant.
7. For simple marketing sites, consider a static site. With no database or plugins, pages can be served almost instantly.

A speed checklist for your next campaign

Before any campaign sends paid traffic to a page, run through these checks. They take about fifteen minutes and protect every pound of the budget:

• Test the landing page in PageSpeed Insights on mobile, and fix anything marked red.
• Check the main image is compressed, correctly sized and in WebP or AVIF.
• Remove pop-ups that cover the content on phones before people have read a word.
• Make sure the form or checkout loads quickly and works on a phone, and send yourself a test enquiry.
• Open the page on a mid-range Android phone using 4G, outside the office.
• Check that tracking and consent work, so you can see which clicks turn into customers.

Speed is part of your brand

People judge a business by how its website feels. A page that appears instantly and responds straight away feels confident and trustworthy; one that stutters makes people wonder what else is slow. That’s why we plan for speed from the first sketch, and why this site is built as fast, plain files with no plugins. If yours needs work, our websites and landing pages service can help.

Frequently asked questions