Performance is a ranking factor
Google has been explicit for years: website performance affects search rankings. In 2021, it made this concrete with Core Web Vitals — a set of specific, measurable metrics that reflect the real experience of visiting a page. Poor performance is now a direct disadvantage in search results.
Beyond rankings, performance affects everything else too. Slow pages lose visitors. Every additional second of load time reduces conversions. The data on this is consistent across industry and business size.
The three Core Web Vitals
Largest Contentful Paint (LCP)
LCP measures how long it takes for the largest visible element on the page to load. This is usually the hero image, a large heading, or a prominent block of text. It is a proxy for how quickly the page feels useful to a visitor.
- Good: Under 2.5 seconds
- Needs improvement: 2.5 to 4 seconds
- Poor: Over 4 seconds
Common causes of poor LCP: large, unoptimised images; slow server response times; render-blocking scripts; and fonts that load late.
Interaction to Next Paint (INP)
INP replaced First Input Delay in 2024. It measures the responsiveness of your page — how quickly it responds when a user clicks a button, taps a link or interacts with any element. A page that looks fast but feels sluggish to interact with will score poorly.
- Good: Under 200 milliseconds
- Needs improvement: 200 to 500 milliseconds
- Poor: Over 500 milliseconds
Common causes of poor INP: heavy JavaScript blocking the main thread; large amounts of third-party scripts; unoptimised event handlers.
Cumulative Layout Shift (CLS)
CLS measures visual stability — how much elements on the page jump around as it loads. You have experienced bad CLS when you go to tap a button and it moves at the last moment, causing you to tap something else instead. It is frustrating, and it signals poor quality to Google.
- Good: Under 0.1
- Needs improvement: 0.1 to 0.25
- Poor: Over 0.25
Common causes of poor CLS: images without defined dimensions; ads or embeds that load in and push content down; web fonts that cause text to reflow when they load.
How to measure your Core Web Vitals
Google Search Console
The Core Web Vitals report in Google Search Console shows your real-world performance data, grouped by page type. This is the most important source because it uses actual visitor data from Chrome users — not a simulated test. If Search Console shows a problem, it is a real problem affecting real visitors.
PageSpeed Insights
Google's PageSpeed Insights tool (pagespeed.web.dev) analyses any public URL and gives you both lab scores (simulated) and real-world field data where available. It also provides specific recommendations for what to fix, which makes it a practical starting point for improvement.
Lighthouse
Built into Chrome DevTools, Lighthouse runs a lab test of your page and provides detailed performance scoring alongside accessibility, SEO and best practice checks. Useful for developers making changes and wanting immediate feedback.
What to do if your scores are poor
Start with your images
Images are the single most common cause of poor performance on small business websites. Ensure every image is compressed appropriately, served in a modern format like WebP, and sized to the largest dimension it will ever be displayed at. Never upload a 4MB photograph to a website.
Reduce third-party scripts
Every third-party script — chat widgets, marketing tools, social embeds, analytics — adds load time and can delay interactivity. Audit what you actually use and remove anything that is not delivering clear value. Load non-essential scripts after the main page content.
Use a fast hosting provider
Time to First Byte (TTFB) — how quickly your server responds — affects LCP directly. If your server response is slow, no amount of front-end optimisation will fully compensate. A modern hosting provider with servers close to your users is important.
Define image and media dimensions
Always specify width and height attributes on images and other media. This reserves space in the layout before the content loads, preventing the layout shifts that cause poor CLS scores.
The business case for performance
Beyond SEO, the business case for performance is straightforward. Google's own research found that pages that load in one second convert three times better than pages that take five seconds. For a business that relies on its website to generate enquiries, every second of load time has a measurable impact on revenue.
A well-built custom website, optimised from the start, will typically score 90 or above on all three Core Web Vitals. This is achievable — it just requires the right technical approach from the beginning, rather than trying to optimise a bloated platform after the fact.