How fast should a website load? The targets that matter

Aim for the main content of each page to appear within 2.5 seconds on a phone. Google also asks for a page that responds to taps within 200 milliseconds and does not jump around while it loads. Those are the published targets, and they are judged on real visitors, not on your own broadband.

A slow site probably costs you sales, but the size of the cost varies by business, so measure your own pages before you pay for fixes. This guide gives you the targets, the evidence, and a 30-minute check you can do this week.

The short answer: three targets

Google's Web Vitals set out three measures. A page counts as good when it meets all three:

• Largest Contentful Paint (LCP): 2.5 seconds or less. This is how long the biggest thing on the screen, usually a main image or headline, takes to appear.
• Interaction to Next Paint (INP): 200 milliseconds or less. This is how quickly the page reacts when someone taps or clicks.
• Cumulative Layout Shift (CLS): 0.1 or less. This is how much the page moves around while it loads, such as a button shifting just as you tap it.

Google judges these at the 75th percentile of page loads, split across mobile and desktop. In plain terms, three in four visits need to be at least that good. INP became an official Core Web Vital in March 2024.

You will often hear that a site should load in 3 seconds. That is a rough rule, not the official one. Google's older mobile research reported that 53% of mobile visitors abandon a page that takes longer than 3 seconds to load. That figure is dated, so treat it as a rule of thumb. The 2.5-second LCP target is the one to work to.

Why phones decide your score

Most of your visitors are on phones. Ofcom found that smartphones accounted for 77% of all UK adult online time on the average day in May 2025, up from 75% the year before.

Phones have slower processors and often weaker connections than your office computer. A site that feels fine on your desktop can still fail on a phone on the train.

Some of those visitors have no other device. Ofcom reports that 18% of UK adults who go online do so only on a smartphone. In 2024, 49% of those smartphone-only users said they struggled to complete forms on a phone compared with a laptop or PC. A slow, jumpy form is a bigger problem for them than for anyone else.

If your site also looks wrong on phones, our guide to fixing a website that looks bad on mobile covers the layout side.

How many sites actually pass

Not many. In the 2025 Web Almanac, from the HTTP Archive, 48% of mobile sites and 56% of desktop sites had good Core Web Vitals. So if your site fails, you are in the majority. Passing is still a realistic aim.

The same data shows where the trouble usually lies. On mobile, 62% of sites had a good LCP, 77% a good INP and 81% a good CLS. Loading speed is the usual weak point, so start there.

The share of mobile sites passing has risen from 36% in 2023 to 44% in 2024 and 48% in 2025. Competitors are getting faster.

Your home page is not your whole site

On mobile, 45% of home pages and 56% of secondary pages had good Core Web Vitals, according to the same Web Almanac data. Pages differ, so test the ones that bring in money, not just the front page.

Does speed really affect sales?

The evidence points that way, with caveats. Shopify analysed actively selling stores and found that for every 100 milliseconds slower a store loads, conversion tends to be about 3.5% lower. In a second analysis, stores with a 2.5-second LCP reported roughly 30% lower conversion than stores with a 1.5-second LCP. Shopify excluded the slowest 5% of stores and controlled for the other Core Web Vitals.

A Google-commissioned study of 37 brand sites and more than 30 million sessions, from late 2019, linked a 0.1-second mobile speed improvement to an 8.4% rise in retail conversions and a 10.1% rise in travel conversions. It also linked it to a 9.2% rise in retail average order value.

What these figures do not prove

• They show association, not proof. Better-run stores may be both faster and better at selling.
• The figures are for retail and travel. A plumber's enquiry form may behave differently.
• Figures vary slightly between summaries of the Google-commissioned study, so use them as direction, not as a forecast.

The fair reading is that faster pages tend to sell more, and the effect is worth checking on your own site. For wider context on what to expect, see our guide to a good conversion rate for a small business website.

Lab score or real visitors: which to trust

PageSpeed Insights shows two sets of numbers, and they often disagree.

• Field data comes from real visitors over recent weeks. This is what Google judges you on.
• Lab data is a single test run in controlled conditions. It is useful for finding causes, but it is one test, not a verdict.

If your site is small, there may be no field data at all. In that case, use the lab score as a guide and aim for the same targets.

A fix also takes time to show in field data, because it covers a rolling window of real visits. Expect weeks, not days.

What usually makes small sites slow

These are common causes, in no particular order:

• Large images. Photos uploaded straight from a camera or phone, often several megabytes each, are a frequent culprit.
• Third-party scripts and apps. Chat widgets, tracking tags, review apps and pop-up tools each add code that has to load.
• Slow server response. Cheap hosting or a heavy theme can delay everything before the page even starts to draw.

Images are usually the cheapest fix. Resize them to the size they are shown at and compress them before uploading.

A 30-minute check you can do yourself

1. List your three most important pages: the ones where people buy, book or enquire.
2. Run each through PageSpeed Insights on the mobile tab. Write down LCP, INP and CLS.
3. Read the field data first. If it is missing, note that and use the lab figures.
4. Look at the list of opportunities. Note whether images, scripts or server response come up most.
5. In your analytics, split conversions by page speed band if your tool allows it. Check whether faster visits convert better on your site.
6. Run our free website check to see how speed sits alongside the other problems on the page.

You can also test the phone experience with our mobile-friendly test.

When to fix it and when to leave it

• Fix it now if your money pages miss the LCP target, especially if most visitors arrive on phones.
• Fix it soon if LCP is close to 2.5 seconds but layout shift or tap response fails. These are often quick wins.
• Leave it for now if all three measures pass and your enquiries or sales are steady. Look at clarity and trust instead, as in our guide to why a website is not converting.

If the site is slow because of its age or the platform it is built on, small fixes may not be enough. Our guide on whether you need a new website or just a few fixes will help you decide.

AgoraScan's free check gives your site a score and the top problems with screenshots in about 2 minutes, including slow loading on phones. A full audit lists every issue with the fix.

Questions people ask

Is 3 seconds a good website load time?

It is a reasonable rough rule, but Google's official target is a main-content load of 2.5 seconds or less, measured on real visitors. Aim for that on your most important pages, on mobile.

Does website speed affect SEO?

Google publishes Core Web Vitals as measures of page experience, so speed is something it looks at. This guide does not cover how much weight it carries in rankings, and fast pages are worth having for visitors in any case.

Why is my PageSpeed Insights score different from what visitors see?

PageSpeed Insights shows lab data from one test and field data from real visitors. They can differ because your visitors use different phones and connections. Trust the field data where it exists.

How long does it take for speed fixes to show up?

Field data covers a rolling window of real visits, so it takes weeks to reflect a fix. The lab test updates straight away, so use it to confirm the change worked.

Sources

1. Web Vitals, Google, web.dev
2. Website speed crisis 2025 (summary of the HTTP Archive Web Almanac 2025 Performance chapter), SiteQwality (2025)
3. Online Nation 2025, Ofcom (2025)
4. Adults' Media Use and Attitudes 2025, Ofcom (2025)
5. Store Speed and Conversion: What the Data Shows, Shopify (2026)
6. Shopify Site Speed: Why Faster Storefronts Convert Higher, Shopify (2026)
7. Milliseconds make millions (summary of a Google-commissioned study and Google mobile speed research), Make it Loud (2019)