Your site feels slow. You have been told it is slow. Someone has offered to fix it for a number that seems high for something you cannot see.
Before spending anything, it is worth knowing that this is a measurable question with a specific answer. Website speed is one of the few technical problems where you can find the actual cause yourself, in about twenty minutes, without any expertise at all.
Measure before you believe anyone
Google’s PageSpeed Insights is free, needs no account, and gives the same data any consultant would start from. Put your homepage in, then do the same for your busiest interior page, because they often differ enormously.
Ignore the score. Everyone fixates on it and it is the least useful thing on the page. A number out of a hundred tells you how you compare to an ideal, not what is wrong with you.
Read the opportunities and diagnostics underneath instead. That list is the actual answer, in plain terms, ranked by how much time each would save.
Check the phone number, not the desktop one
The tool reports mobile and desktop separately, and the mobile figure is the one that matters. Most visitors arrive on a phone, often on mobile data, on a device considerably less powerful than the laptop you are checking from.
A site that feels instant on your desk and takes eight seconds on a phone is the most common situation there is, and it is invisible to the person who owns the site.
The four causes, in order of likelihood
Images
By a distance the most common, and the cheapest to fix.
A photo from a modern phone can be four or five megabytes. Uploaded directly, it stays that size, and the browser downloads all of it before shrinking it to fit a space a fraction as wide. Ten of those on a page and nothing else matters.
Look for “properly size images”, “efficiently encode images” or “serve images in next-gen formats” in the report. If those are at the top, you have found it, and it is usually resolved in an afternoon.
Too much code loading on every page
Shows up as “reduce unused JavaScript” or “reduce unused CSS”.
This is nearly always plugins and page builders loading their assets everywhere regardless of whether a page uses them. A slider plugin loads on pages with no slider. A form plugin loads on pages with no form.
It is a real cause and a fixable one, and it is an accumulation problem rather than a platform problem.
The server is slow to answer
Look for “initial server response time” or “reduce server response time”.
This one is not about your site at all. It is the gap between the browser asking and your host beginning to reply. If that number is high, no amount of image work will help, because the delay happens before your images are even requested.
The cause is usually very cheap shared hosting, where hundreds of sites share one machine. Moving host is the fix, and it is often less expensive than people expect.
Third-party scripts
Chat widgets, analytics, tag managers, embedded videos, tracking pixels, review widgets, a booking embed.
Each was added for a reason and each adds a request to somebody else’s server, whose speed you do not control. Sites that have run marketing campaigns for a few years tend to accumulate several that nobody is using any more.
The order to fix things in
Images, then unused third-party scripts, then hosting, then code. That is roughly cheapest and most effective first.
Resist buying a caching plugin as step one. Caching is genuinely useful, but applied to a page carrying five megabytes of unoptimised photographs it hides the problem from repeat visitors and does nothing for the first-time visitor you were trying to impress.
Whether it is worth caring about
Honestly: it depends on where you are starting.
Going from eight seconds to three is transformative, because a large share of visitors leave before the page appears at all. Going from two seconds to one is a rounding error nobody will feel, and chasing a perfect score is a hobby rather than a business decision.
Speed also has a floor rather than a ceiling as a commercial matter. A fast site that nobody can find, or that gives visitors no reason to get in touch, is still not working. If the site is quick and the enquiries are not arriving, the problem is somewhere else entirely.
The honest summary
Run the test, read the list under the score, and check the mobile figure. In most cases the answer is images, and you can fix that yourself without paying anybody.
If the top item is server response time, no plugin will save you and the conversation is about hosting instead. Hosting is covered as part of the website design work here, set up properly from day one.
If you have run it and the list means nothing to you, send what it says and you will get a plain reading of which items actually matter for your site and which are noise.
Common questions
What is the most common cause of a slow small business site?
Images, by a distance. A photo straight off a phone can be four or five megabytes, and the browser downloads all of it before shrinking it to fit a space a fraction as wide.
Does the PageSpeed score matter?
Less than the list underneath it. The score compares you to an ideal; the opportunities tell you what is actually wrong, ranked by how much time each would save.
Will a caching plugin fix it?
It helps, but applied to a page carrying five megabytes of unoptimised photographs it mostly hides the problem from repeat visitors and does nothing for the first-time visitor you were trying to impress.