This is the most expensive fault on most small business websites, and almost nobody spots it, because on the office broadband it looks perfectly fine.
Where your customers actually are
Not at a desk. They are standing in a garden holding a phone with two bars, or in a car park, or on a bus. That is where somebody decides whether to ring a plumber.
A site that appears instantly at your desk can take eight seconds there, and a good proportion of people will not wait. They go back and press the next result, which is your competitor. You never learn it happened, because a visitor who left is invisible to you.
What is nearly always to blame
Photographs straight off a camera or phone. This is the cause perhaps four times out of five.
A modern phone takes pictures several thousand pixels wide. On a website that image is displayed a few hundred pixels wide. If nobody resized it first, the visitor downloads the enormous one and their phone shrinks it, which wastes both their data and their patience.
Six large photographs handled that way can be twenty times the weight of the entire rest of the page.
The fix is simply to resize before uploading. Any decent builder should do this for you. If you are doing it yourself, aim for around 1,600 pixels wide for a big image and considerably less for a small one.
The other three causes
Plugins nobody uses. Every one adds code to every page, whether or not the page needs it. Sites accumulate them the way lofts accumulate boxes.
Sliders and video backgrounds. A rotating banner at the top is heavy, and research has been consistent for years that almost nobody looks past the first slide. It is a lot of weight for very little.
Cheap hosting. The five pound a month sort puts hundreds of sites on one machine. Everything is slow and no amount of tidying fixes it.
How to test it honestly
Not on your own computer, and not on your own wi-fi. Both are far kinder than reality.
Take your phone, turn wifi off so you are on mobile data, stand somewhere with a middling signal, and open your website. Count. Anything past three seconds before you can read something is costing you money.
For a second opinion, Google’s PageSpeed Insights is free and will tell you what is heaviest. Ignore the score, which is discouraging for everyone, and read the list of largest items instead. That list is the actual job.
Why it matters twice over
Speed costs you customers directly, and it costs you a second time through search: how quickly a page becomes usable is one of the things Google measures when deciding where to put you.
So a slow site is seen by fewer people, and loses more of the ones who do see it.
What good looks like
Something readable within about a second and a half on a phone on mobile data. That is achievable for an ordinary small business site without anything clever: sensible images, few plugins, decent hosting.
It is not a specialism. It is mostly just not being careless with photographs.
If you want a straight answer on yours, send me the address. I will tell you what is slowing it down and whether it is worth fixing, and I do not charge for looking.