Every second counts.

A visitor decides whether to stay on a page or go back to the search results within the first 2-3 seconds. If the screen is blank and the buttons jump around, the lead goes to a competitor. Website loading speed is not a minor detail for the developer to worry about; it is a factor that directly affects revenue and rankings.

Let's look at which metrics search engines evaluate, how to check a site in 10 minutes, what slows it down and which steps give the most noticeable gains.

Why speed affects leads

A slow site loses people before they have even seen the offer, and search engines are less likely to rank such pages high. Both traffic and conversion suffer at once.

User behavior

On a smartphone, a person opens several tabs from the search results and stays where the content appeared first. Every extra second lowers the chance that they will scroll down to the form.

Search rankings

Google uses Core Web Vitals as a ranking signal, while Yandex relies on behavior: a quick return to the search results tells it the page did not help. That is why speed is part of a website's SEO optimization rather than a separate task.

Bounces

Yandex Metrica counts a visit as a bounce if it lasts less than 15 seconds and covers one page. If the bounce rate on mobile is noticeably higher than on desktop, check the loading time first.

Conversion

Speeding up a site almost always pays off: the same ad budget brings more people who waited for the page to load and filled in the form.

What Core Web Vitals are

These are three Google metrics that describe a visitor's real experience: how quickly the main content becomes visible, whether the layout jumps, and how the page responds to actions. They are assessed at the 75th percentile, meaning at least three quarters of visits must meet the threshold.

LCP: loading speed

LCP shows when the largest element on the first screen has rendered: a banner, a product photo or a heading. Most often it is spoiled by a heavy image in the header.

CLS: layout stability

CLS measures how much blocks shift during loading. A person reaches for the "Buy" button, a banner loads above it, and their finger lands on the ad.

INP: responsiveness

INP replaced FID in 2024 and measures the delay between a click or input in a field and the interface's response. A poor value usually points to overloaded JavaScript.

What counts as normal

Google considers a good result to be LCP under 2.5 seconds, INP under 200 milliseconds and CLS no higher than 0.1. You need to meet all three at once.

What counts as poor

The red zone is LCP over 4 seconds, INP over 500 ms and CLS above 0.25. Values in between are marked as needing improvement, and they are already worth working on.

How to check speed

Three free tools are enough: PageSpeed Insights for real-user data, Lighthouse for finding causes, and Yandex Metrica for linking speed to behavior. Check the home page, the catalog, a product page and a service page: different templates slow down in different ways.

PageSpeed Insights

The service shows field data for 28 days and a lab test. The first block matters more, since that is what search takes into account. With low traffic there will be no field data, and you will have to rely on the lab results.

Lighthouse

The tool is built into Chrome DevTools and breaks the page down point by point: which files block rendering, which images are too heavy, how much unnecessary code weighs.

Metrica

The "Page load time" report in the "Monitoring" section shows how the site opens for your visitors on different devices and in different regions of Russia.

What to look at

To avoid drowning in reports, keep five points in focus:

• field LCP, INP and CLS specifically for mobile;
• server response time, to rule out the hosting;
• page weight and number of requests;
• scripts and styles that block the first screen;
• changes after each update.

What not to trust

The 0 to 100 score in PageSpeed is not the goal: a score of 60 with green field metrics is better than 95 in the lab with red real-world data. Take 3-5 measurements and use the average.

What slows a site down

What slows a site down most often? Heavy images, excess JavaScript, fonts, video and third-party widgets. Fixing the first two is usually enough for the metrics to improve noticeably.

Images

A 4-6 MB camera photo uploaded without processing can single-handedly fail LCP. The second problem is PNG where WebP would do, and images without specified dimensions, which drive up CLS.

Scripts

Counters, chats, pixels and sliders added "just in case" load before the content and occupy the processor. On an inexpensive phone, they are exactly what turns INP red.

Fonts

Three typefaces with four weights each mean dozens of requests. While the files load, the text is invisible or gets redrawn and shifts neighboring blocks.

Video

A background video on the first screen sometimes weighs more than the entire page. Use a lightweight placeholder image and load the video itself on click.

Third-party widgets

A live chat, a quiz, a map and external reviews pull code from other people's servers that you do not control. Keep only the ones that actually bring in inquiries.

How to speed up a site

If you are deciding how to speed up a site without extra spending, start with images, then set up caching and lazy loading, and only after that move on to the code.

Image compression

Image optimization is the fastest win: converting to WebP or AVIF, scaling down to the actual on-screen size, separate versions for smartphones. The weight of graphics often drops 3-5 times without any visible loss of quality.

Caching

Website caching spares the server from assembling the page on every visit and spares the browser from downloading styles and scripts again. 1C-Bitrix and WordPress have built-in tools for this.

Lazy loading

Images below the first screen load only when a person scrolls down to them. The key is not to apply this technique to the main image at the top, or LCP will get worse.

What you can do yourself

Some of the work does not require a developer and fits into one evening:

1. resize photos before uploading;
2. remove unused plugins and widgets;
3. enable caching in the CMS settings;
4. turn off video autoplay;
5. keep one or two fonts instead of five.

What to leave to a developer

Minifying scripts and styles, deferred JavaScript and server configuration require access to the code, and a mistake here breaks forms and the cart. If a site is built on an outdated template, speeding it up can cost more than building a new one. When comparing website development prices from different teams, ask which Core Web Vitals values they will show at handover: competent website development builds in speed already at the layout stage.

Mobile speed

Mobile speed matters more than desktop speed: Google indexes sites by their mobile version, and commercial queries are increasingly made from smartphones.

How it differs from desktop

A phone's processor is several times weaker than a laptop's, and the connection is unstable. The same page can show an LCP of 1.8 seconds on a computer and 4 seconds on a smartphone.

What to check

Look at the mobile tab in PageSpeed and at device emulation in Chrome with a throttled network. Make sure the phone is not served huge banners meant for desktop. The basic rules are collected in the article on SEO optimization for mobile devices.

Mobile internet

In the subway and outside the city, the connection drops to 3G levels. Test in slow 4G mode: if the first screen takes longer than 3 seconds to appear, some people will leave.

Low-end devices

On budget Android smartphones, heavy JavaScript takes the longest to execute, and that is exactly where INP goes over 200 ms. Keep an inexpensive phone at hand for manual checks.

How often to check

After launch, after every noticeable change, and on a schedule: briefly once a month, in detail once a quarter. A site slows down gradually, with banners, plugins and counters.

After launch

Take the first measurement on release day. If you are only planning to build a website, write speed requirements into the technical specification: a turnkey website should end with a Core Web Vitals check. When comparing website prices from contractors, ask whether this check is included in the estimate. The full checklist is in the article on a technical website audit.

After changes

A new widget, a header redesign or a CMS update is a reason to compare the metrics "before" and "after." That way the culprit is found right away, not six months later.

Once a month

15 minutes is enough: run the key templates through PageSpeed and check Metrica. A drop of more than 20% is a signal to investigate immediately.

Once a quarter

You need a full review: Lighthouse for all page types, an audit of scripts, and the Core Web Vitals report in Search Console. It is convenient to combine this with scheduled SEO work, since search engine optimization (SEO) and speed rely on the same data.

Conclusion

Speed affects bounces, conversion and rankings, so LCP, INP and CLS should be kept in the green zone, above all on mobile. Start with images, caching and unnecessary widgets, and hand the code over to specialists; there is an example in the case study on how to make a website work at 100%.

Since 2015, the epic name. team has been developing websites for companies in Moscow and other cities, and our website development starts with speed requirements. You can order SEO optimization for a live project, order turnkey website development, or order a turnkey website built from scratch. The cost of website development and the price of SEO optimization depend on the number of templates, so we start with a measurement. Details are on the website development page.