Why is my website slow on mobile?

Phones expose what desktops hide

A phone has far less processing power than a laptop, and it often loads your page over a cellular signal. Google's lab test models this on purpose: Lighthouse throttles the connection to what it calls Slow 4G, roughly the bottom quarter of 4G connections, with 150 milliseconds of latency.

The gap is large across the web. The HTTP Archive's 2025 Web Almanac measured median Total Blocking Time, the time scripts lock up the processor, at 1,916 milliseconds on mobile pages against 92 on desktop. The average mobile page weighed about 2.28 megabytes, above the 1 to 1.5 megabyte range the authors describe as commonly recommended.

The usual culprits

Check these first. Each one is common on small business sites and easy to spot in a speed report:

• A huge hero image or video. The largest item on the first screen is usually what Google times as Largest Contentful Paint, and a photo straight from a camera or a background video can take seconds on cellular.
• Lazy loading in the wrong place. web.dev warns never to lazy-load the main image, because it delays the most important picture on the page.
• Too many scripts. Chat bubbles, review carousels, heatmaps, social feeds and several analytics tags each add requests and processor time, and web.dev calls third-party scripts a common cause of slow pages.
• Page builder output. The Almanac reports that builders often add complex markup and larger CSS and JavaScript bundles.
• Slow server response. PageSpeed Insights rates time to first byte as good at 800 milliseconds or less, and cheap hosting can blow past that before the page starts to draw.
• Images without set sizes. The Almanac found the median page has two images with no declared dimensions, which lets the layout jump around as they arrive.

Find your own bottleneck in a few minutes

You do not need a developer to see where the time goes. Work through these steps on your homepage and your busiest service page:

• Open PageSpeed Insights, enter the page address and keep the Mobile tab selected.
• Check whether the page passes the Core Web Vitals assessment from real visitors, if your site has enough traffic to show one.
• Find the Largest Contentful Paint element and its breakdown. The breakdown splits the wait into stages, so you can see whether the image itself is slow or something is blocking it.
• Open the third-party insight to see which outside services run and how much time each one takes.
• Load the page on your own phone over cellular, not Wi-Fi, and count how long it takes before you can see the phone number.

Fixes in order of payoff

Start at the top of this list, since the early items usually take the least work, and none of them requires a new website:

• Resize and compress the hero image, serve a modern format such as WebP, and give it high fetch priority, which web.dev recommends for the image most likely to be the Largest Contentful Paint.
• Remove scripts you no longer use, and load chat and review widgets only after a visitor interacts with the page.
• Cut plugins and add-on packs down to the ones that earn their place.
• Set a width and height on every image so the layout holds still.
• Move to faster hosting or add caching if the server response is slow.
• Limit web fonts to the styles and weights you actually use.

When the platform is the limit

Some sites hit a floor. If a theme or builder loads its framework on every page, tuning removes the extras but not the foundation, and the Almanac notes that builder improvements have not fully closed the gap with tightly controlled builds. That is when a rebuild earns its cost. Modern Apex hand codes sites for exactly this reason: each page carries only what it needs.

Keep reading

• What is a good PageSpeed score?
• What is Elementor, and does it slow down websites?
• How do I know if my website is losing customers?
• Web design from Modern Apex