Why is my website slow on phones?

Facts checked on October 22, 2026, each against its source. Every number links to where it came from.

How big the gap is

The HTTP Archive's Web Almanac measures the web every year. In its 2025 edition, 48% of sites passed Google's speed checks on phones, against 56% on desktop computers¹. The gap is widest in how quickly a page reacts to a tap: 77% of sites react quickly enough on phones, against 97% on desktop¹. For loading time, the report calls the gap "consistent with the combined effects of slower networks and less capable devices on mobile"¹.

What counts as slow

Google measures three things, and calls them Core Web Vitals:

• Loading. The largest image or block of text should appear within 2.5 seconds; over 4 seconds is poor.²
• Reacting. A tap or click should get a visible response within 200 milliseconds; over 500 is poor.²
• Staying still. Content shouldn't jump around as the page loads: a layout shift score of 0.1 or less is good, over 0.25 is poor.²

Each is judged at the 75th percentile of visits, so most visitors have to get the good result, not only the lucky ones². Google says these are used by its ranking systems, but that it still shows the most relevant result even when its page experience is poor³. Speed alone is unlikely to outrank a better answer, but the people who do arrive still wait for the page.

Measure it the way a phone sees it

Your own phone on your office Wi-Fi is the wrong test, and your laptop is worse. Google notes that on fast connections and desktop hardware, the cost of heavy scripts may not show⁴.

Use Google's free PageSpeed Insights instead, and read its two halves separately. The top half is field data from real Chrome users over the previous 28 days; the bottom half is a lab test on one simulated device and connection, which is useful for finding causes but may not match what people actually see⁵. The lab test slows the processor 4 times and simulates a connection with 150 milliseconds of latency and 1.6 Mbps of download speed⁶, roughly a mid-range phone on a middling signal.

The usual causes, biggest payoff first

Images

The median home page on a phone weighs 2.6 MB, and 911 KB of that is images⁷. Most of the fix is sending a phone a phone-sized picture:

• Offer several sizes of each image and let the browser choose (the srcset and sizes attributes)⁸. Many site builders do this for you when you upload one large original.
• Use WebP or AVIF, which compress better than JPEG and PNG⁹.
• Never lazy-load the main image at the top of the page; mark it as high priority instead¹⁰. About 16 to 17% of pages lazy-load that image anyway¹, which delays the first picture visitors see.
• Give every image a width and height¹¹, so the page doesn't jump when it arrives.

Scripts from other companies

More than nine in ten pages load something from a third party¹²: chat widgets, video players, booking tools, maps, review badges, ad and tracking tags. Google calls third-party scripts a common cause of slow pages¹³.

• Remove what you no longer use. Old tracking tags are common leftovers.
• Load the rest after the page. A chat widget or a video can show a lightweight placeholder and load the real thing on a tap: in Google's example, a YouTube placeholder weighs 3 KB and the full player 540 KB¹⁴.

A slow server

Before a phone can draw anything, your server has to answer. Google treats 0.8 seconds or less as a good first response¹⁵, and only 44% of sites manage that on phones¹. On WordPress the usual fix is caching: WordPress's hosting handbook recommends a page cache in front of the site and a persistent object cache, which managed hosts commonly offer¹⁶. On cheap shared hosting, a better plan is sometimes the whole fix.

Fonts

Each custom font is another download. Show text straight away in a fallback font while the custom one loads (font-display: swap), and deliver the font early enough that the swap doesn't shift the page. Use fewer font files, and consider system fonts for body text¹⁷.

Things that jump

Content that moves while you're reading is the third Core Web Vital. The common causes are images without a set size, and embeds, ads or forms that load late into space nobody reserved. Reserve the space, with a set size or a minimum height¹⁸.

Heavy pages that ignore taps

A page can look loaded and still not respond. Any piece of script work longer than 50 milliseconds blocks the page from reacting while it runs¹⁹, and on phones those pile up: the median phone page spends 1,916 milliseconds blocked by scripts in the lab test, against 92 on desktop¹. Cutting plugins, sliders and animations can help more than changing a setting.

Wix, WordPress and the rest

It matters somewhat. In the 2025 report, 74% of Wix sites passed the speed checks on phones, against 45% of WordPress sites²⁰. WordPress isn't slow by itself; its sites vary with the theme, the plugins and the page builder they're built with. If yours is slow, start by switching off plugins one at a time and measuring again.

Keeping it fast

Sites get slower a little at a time, with each new plugin, widget and photo, so measure again after every change. Nodium measures it every week: its weekly check loads your home page and your 2 most-visited pages as a phone, with the processor slowed 4 times, and lists any that are slow by Google's lines for poor. It doesn't slow the network, so a phone on a weak signal can be slower still²¹, and its insights point out a slow page that's losing phone visitors. To try one page now, the free site check measures it on a phone, with no account.