Core Web Vitals and Revenue: What the Data Actually Says

When Vodafone ran an A/B test on their Italian e-commerce site, sending 100,000 clicks per day to an optimised landing page and 100,000 to the original, the results were unambiguous. A 31% improvement in Largest Contentful Paint led to 8% more sales, a 15% increase in leads, and an 11% improvement in cart visits. No redesign. No new features. Just a faster page.

That kind of result raises an obvious question: is this a one-off, or is there a predictable, measurable relationship between how fast your website loads and how much money it makes?

The answer, backed by years of published data from Google, Deloitte, and dozens of major companies, is clear. Speed is revenue. And we now have the specific numbers to prove it.

What Core Web Vitals actually measure

Google uses three metrics to assess the real-world experience of people visiting your website. Together, they are called Core Web Vitals.

Largest Contentful Paint (LCP) measures how long it takes for the main content of a page to appear on screen. This is the moment a visitor sees something useful — a headline, a product image, or a hero section. Google considers anything under 2.5 seconds "good" and anything over 4 seconds "poor."

Interaction to Next Paint (INP) measures how quickly a page responds when someone taps a button, clicks a link, or types into a form. If your page feels sluggish when a visitor tries to do something, INP captures that. Under 200 milliseconds is "good"; over 500 milliseconds is "poor." INP replaced the older First Input Delay metric in March 2024.

Cumulative Layout Shift (CLS) measures visual stability — whether page elements jump around as the page loads. If you have ever tried to tap a button on a mobile site only for the page to shift and send you somewhere else, that is a CLS problem. Below 0.1 is "good"; above 0.25 is "poor."

These three metrics cover the essential experience: did the page load quickly, did it respond when I interacted with it, and did it stay still while I was using it?

Google assesses your site using real user data from Chrome browsers. They use the 75th percentile — meaning at least 75% of your visitors need to have a "good" experience for your site to pass. As of September 2025, only 53% of websites pass all three thresholds.

The evidence: what published case studies actually show

This is not theory. Major companies across multiple sectors have published their results, often in partnership with Google. The numbers are specific and the methodology is transparent.

Vodafone: 8% more sales from faster loading

Vodafone Italy ran a controlled A/B test, splitting traffic equally between a performance-optimised landing page and the original. The optimised page achieved a 31% improvement in LCP. The business results: 8% more sales, 15% more leads, and 11% more cart visits. As Vodafone's team put it: "The introduction of LCP as the main KPI for page performance made it possible to significantly improve the customer experience of our e-commerce."

Rakuten 24: 53% more revenue per visitor

Rakuten 24, one of Japan's largest online retailers, invested in Core Web Vitals improvements and measured the impact rigorously. Revenue per visitor increased by 53.37%. Conversion rate increased by 33.13%. They found that achieving a good LCP score could lead to up to a 61% increase in conversion rate and a 26% increase in revenue per visitor. These are not marginal gains.

Swappie: 42% increase in mobile revenue

Swappie, a European refurbished phone retailer, had spent years adding features without focusing on performance. When they noticed mobile results lagging behind desktop, they shifted priorities. After reducing LCP by 55%, CLS by 91%, and FID by 90%, mobile revenue increased by 42% within three months. Their relative mobile conversion rate improved from 24% to 34%.

AliExpress: 15% reduction in bounce rate

AliExpress improved their CLS by 10 times and doubled their LCP performance. The result was a 15% reduction in bounce rate — fewer visitors leaving immediately because the page was slow or unstable.

Yahoo! Japan News: 15% more page views per session

Yahoo! Japan focused on reducing layout shifts across their news platform. After achieving a 98% reduction in pages with poor CLS scores, they measured a 15% increase in page views per session and a 13% increase in session duration. For an advertising-funded publisher, more page views per session directly translates to more revenue.

NDTV: 50% reduction in bounce rate

Indian news publisher NDTV improved their LCP by 55%, bringing it from 3.0 seconds to 1.6 seconds. The outcome was a 50% reduction in bounce rate — a dramatic shift in audience engagement from a single performance metric.

Redbus: 80-100% improvement in mobile conversions

Redbus, a transport booking platform operating across multiple countries, fixed their CLS (reducing it from 1.65 to zero) and cut their Time to Interactive from roughly 8 seconds to 4 seconds. The impact was an 80–100% improvement in mobile conversion rate across their global properties, alongside significant gains in domain rankings.

The Telegraph: measurable conversion uplift from CLS fixes

The Telegraph, one of the UK's largest publishers, improved their 75th percentile CLS by 250% (from 0.25 to 0.1). Their proportion of pages passing CLS thresholds grew from 57% to 72%. Analysis using Quantum Metric showed that removing poorly performing code increased page performance by 17%, which created a 1.35% uplift in conversions. For a publisher handling millions of sessions, even small percentage improvements represent substantial revenue.

iCook: 10% more ad revenue

Taiwanese recipe platform iCook improved their CLS by 15% through better ad slot sizing and pre-allocated space in the UI. The result was a 10% increase in ad revenue — directly attributable to improved layout stability.

The Deloitte study: even 0.1 seconds matters

In 2020, Deloitte published "Milliseconds Make Millions," a study analysing over 30 million user sessions across 37 leading European and American brand sites. Their central finding: a 0.1-second improvement in load time improved progression rates across the entire purchase funnel.

The sector-specific results were striking:

• Retail: conversions increased by 8.4% and average order value increased by 9.2%
• Travel: conversions increased by 10.1%
• Luxury brands: page views per session increased by 8.6%, with a 40.1% increase in users moving from product detail to add-to-basket
• Lead generation: bounce rate improved by 8.3%

These are not improvements from a complete site overhaul. These are the gains from shaving one-tenth of a second off load time.

The broader pattern: every second costs you money

Research from Portent, based on analysis of 20 websites and over 100 million page views, found that website conversion rates drop by an average of 4.42% with each additional second of load time between 0 and 5 seconds. A site that loads in 1 second has a conversion rate 3 times higher than a site that loads in 5 seconds. For B2B sites, that multiplier increases to 5 times.

Google's own data shows that 53% of mobile users abandon a page if it takes more than 3 seconds to load. The relationship between speed and user behaviour is not linear — it is exponential. The first few seconds matter enormously, and the penalty for slow loading compounds rapidly.

How Core Web Vitals affect your search rankings

Since 2021, Core Web Vitals have been an official ranking signal in Google's algorithm. They are part of the broader "page experience" signals, alongside mobile-friendliness, HTTPS, and the absence of intrusive interstitials.

Google has been careful to say that content relevance still matters most. A slow page with excellent content will still rank above a fast page with thin content. But when multiple pages compete for the same query with comparable content quality, performance becomes a tiebreaker — and in competitive markets, tiebreakers determine who appears on page one.

The practical effect is compounding. Better Core Web Vitals lead to better rankings. Better rankings lead to more traffic. More traffic to a faster site leads to more conversions. More conversions justify further investment in performance. It is a virtuous cycle that rewards the organisations who invest early.

The March 2024 core update reinforced this. Sites with poor metrics experienced traffic drops, while those that had invested in performance saw gains. The message from Google is consistent: user experience is a ranking factor, and Core Web Vitals are how they measure it.

Where to start: prioritising by business impact

Not all performance work delivers equal returns. If you are deciding where to invest first, here is a practical framework based on what the data shows.

1. Fix LCP first

LCP has the most direct and well-documented relationship with revenue metrics. The Vodafone, Rakuten, NDTV, and Swappie case studies all show that LCP improvements drive measurable increases in sales and conversions. Common fixes include optimising images, improving server response time, and removing render-blocking resources.

2. Address CLS on high-traffic pages

CLS problems are often caused by ads, images without defined dimensions, or dynamic content that loads late and pushes other elements around. The Yahoo! Japan, Telegraph, and iCook studies show that CLS fixes improve engagement and revenue, particularly on content-heavy and ad-supported pages. These fixes are typically straightforward — reserving space for ads, adding width and height attributes to images, and avoiding late-loading DOM injections.

3. Measure INP on interactive pages

INP matters most on pages where users are actively doing things: filling out forms, filtering products, using configurators, or navigating complex interfaces. If your visitors are mainly reading content, INP may already be fine. But if your conversion flow involves interaction, poor INP will cost you completions.

4. Use real user data, not lab tests

Lab tools like Lighthouse are useful for identifying issues, but they measure synthetic performance under controlled conditions. The Chrome User Experience Report (CrUX) measures what your actual visitors experience. Google uses CrUX data for rankings, not Lighthouse scores. Make sure you are monitoring what Google is monitoring.

5. Test changes with A/B experiments

The most credible case studies — Vodafone, Rakuten, Swappie — all used A/B testing to isolate the impact of performance changes. This is the gold standard. If you cannot run formal A/B tests, at minimum track your Core Web Vitals in Google Search Console alongside conversion data over time, and correlate the trends.

The bottom line

The relationship between Core Web Vitals and revenue is not speculative. It has been measured, published, and replicated across dozens of companies, multiple industries, and various geographies. Vodafone saw 8% more sales. Rakuten saw 53% more revenue per visitor. Swappie saw 42% more mobile revenue. Deloitte proved that even 0.1 seconds makes a measurable difference to conversion rates.

For UK businesses competing in crowded markets — whether in e-commerce, professional services, or lead generation — website performance is not a technical concern to delegate and forget. It is a revenue driver that deserves the same attention as pricing, positioning, and marketing spend.

The good news is that performance improvements often involve known, well-documented fixes. They do not require a full rebuild. And unlike many marketing investments, the results compound: faster pages rank higher, convert better, and create a measurably better experience for every visitor.

The data is clear. The question is whether you act on it.

References

1. Vodafone: A 31% improvement in LCP increased sales by 8% — web.dev
2. How Rakuten 24's investment in Core Web Vitals increased revenue per visitor by 53.37% — web.dev
3. How Swappie increased mobile revenue by 42% by focusing on Core Web Vitals — web.dev
4. The business impact of Core Web Vitals — web.dev (includes AliExpress, NDTV, Redbus, iCook, and Yahoo! Japan data)
5. Improving Cumulative Layout Shift at Telegraph Media Group — web.dev
6. How CLS optimizations increased Yahoo! JAPAN News's page views per session by 15% — web.dev
7. NDTV achieved a 55% improvement in LCP by optimizing for Core Web Vitals — web.dev
8. Milliseconds Make Millions — Deloitte / Google, web.dev
9. Site Speed is (Still) Impacting Your Conversion Rate — Portent
10. Web Vitals — web.dev (metric definitions and thresholds)