Why is it fast for me and slow for others?

Because your browser keeps everything it already downloaded. You never see the first visit, which is the only one a new visitor gets. Test in a private window to get closer to it.

Does it change anything for Google?

Yes. Loading speed is among the signals Google accounts for, measured on real visits rather than in a lab. But the most immediate effect is not there: it is the visitor closing the tab before seeing your page.

How slow is too slow?

Beyond two and a half seconds to show the main element, Google considers it no longer good. In practice, a visitor waiting more than three seconds on a phone leaves.

My site is slow on phones: where to start

On your machine the site opens instantly. A friend tries it and waits four seconds to see anything. You reload on your own phone: fast. You cannot work out where the gap comes from, and you are not even sure the problem is real or just in their head.

It is fast for you because your browser already has everything in memory. For a visitor arriving for the first time, on mobile data, nothing is cached. Nine times out of ten the cause is the same: images that are far too heavy, served at their original size.

Why you cannot see the problem

Your browser keeps everything it has already downloaded from your site: images, fonts, styles. By your second visit there is almost nothing left to fetch.

So you will never see what someone arriving for the first time sees — on a phone, on mobile data, on a train. Yet that is the only visit that counts, because that is the one where people decide whether to stay.

To get close to it: open your site in a private window, on your phone, with wifi off. The gap is often brutal.

The cause, nine times out of ten

Images.

A photo taken on a phone weighs several megabytes and is thousands of pixels wide. Shown in a 400-pixel space on a phone screen, it is scaled down on display — but downloaded whole. The visitor pays for the full file to see a thumbnail.

Three images like that are enough to turn an instant page into a four-second one. And nothing flags it: on your screen, everything looks normal.

It is also what most often delays the main element of the page — the one a visitor waits for to understand where they have landed.

What to ask for, precisely

“Make my site faster” gets you nothing usable. These three do:

Compress every image on the site and resize them to the size they are actually displayed at. Tell me the weight before and after, image by image.

Add lazy loading to images that are not visible when the page opens.

Check that no font blocks the text from showing while it downloads.

The first handles the bulk. The second avoids downloading what nobody will look at. The third removes the most irritating effect: a blank page for a second when the text was ready all along.

Ask for the before and after numbers. Without them you have no way of knowing whether anything changed.

Measure, rather than sense

Feel is not enough here, because it depends on your device, your connection and what your browser already holds.

Two simple markers: count the time between tapping the link and being able to read something useful. Beyond three seconds on a phone, you lose visitors. And look at the total page weight — a few hundred kilobytes is comfortable, several megabytes is not.

Free measurement tools give you those numbers, and more usefully they tell you which specific element is slowing everything down. That beats an overall score, which does not tell you what to fix.

What it actually changes

A slow site does not just lose ranking. It loses people who never saw the page, who will not write to you, and whom you will never hear about — exactly like a broken form.

The difference is that this one is fixed in an evening and does not come back, provided you add one rule to your instructions: every image entering the project gets compressed on the way in, not afterwards.