The verdict in three sentences
Core Web Vitals (LCP, INP, CLS) are not just an SEO criterion: they directly affect the B2B conversion rate, especially on mobile. Taking an LCP from 4 s to under 2.5 s can increase conversion by 8 to 20% and reduce bounce rate. An optimisation project costs 3,000 to 15,000 EUR and generally pays back in under 4 months on a site with significant traffic.
What Core Web Vitals measure
Google assesses three key metrics. LCP (Largest Contentful Paint) measures how fast the main content appears; INP (Interaction to Next Paint) measures responsiveness; CLS (Cumulative Layout Shift) measures visual stability. Here are the 2026 thresholds and their impact.
| Metric | Good | Needs work | Poor | Conversion impact |
|---|---|---|---|---|
| LCP | < 2.5 s | 2.5 - 4 s | > 4 s | High |
| INP | < 200 ms | 200 - 500 ms | > 500 ms | Medium |
| CLS | < 0.1 | 0.1 - 0.25 | > 0.25 | Medium |
| TTFB | < 800 ms | 0.8 - 1.8 s | > 1.8 s | Indirect |
The business stake: every second of load time saved reduces abandonment and increases contact requests.
| LCP improvement | Observed effect on conversion | Effect on mobile bounce |
|---|---|---|
| 5 s → 3 s | +5 to 10% | -10 to 15% |
| 4 s → 2.5 s | +8 to 20% | -15 to 25% |
| 3 s → 1.8 s | +3 to 8% | -5 to 12% |
What a performance optimisation costs
The budget depends on the depth of the work: simple tuning or technical rebuild. Here are the 2026 ranges in the Berlin market.
| Scope | Budget 2026 (EUR) | Duration | Typical LCP gain |
|---|---|---|---|
| Quick wins (images, cache) | 3,000 - 5,000 | 1 - 2 wks | -1 to 1.5 s |
| Front + back optimisation | 6,000 - 10,000 | 3 - 5 wks | -1.5 to 2.5 s |
| Performance rebuild | 10,000 - 15,000 | 6 - 10 wks | -2 to 3.5 s |
| Ongoing perf budget | 800 - 1,500/month | ongoing | Maintenance |
Mini case study
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Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Sophie, digital director of a B2B SaaS vendor in Berlin, runs a site with 60,000 visits/month, a mobile LCP of 4.2 s and a 1.8% conversion rate. After an 8,500 EUR project bringing LCP to 2.3 s, conversion rises to 2.2% (+22%). On 60,000 visits, that is 240 extra leads/year; at 200 EUR of avoided paid cost per lead, the project pays back in under 3 months.
FAQ
Do Core Web Vitals really influence SEO?
Yes, they are part of Google's ranking signals, especially on mobile. Their weight is moderate versus content, but with equal content they act as a tiebreaker, and their effect on conversion is immediate.
What is the most cost-effective lever?
Often images (AVIF/WebP formats, lazy loading) and caching: 3,000 to 5,000 EUR is enough to gain 1 to 1.5 s of LCP, with fast impact on mobile bounce.
Do we need to rebuild the whole site?
Not necessarily. An audit separates quick wins from structural debt. Many sites gain 2 s with targeted optimisations before considering a rebuild.
How do we keep performance over time?
By setting a performance budget (LCP/INP thresholds monitored on every deploy) for 800 to 1,500 EUR/month, otherwise gains erode with each new feature.
Let's scope your project. Send us your URL, monthly traffic and current scores: we will cost a Core Web Vitals optimisation plan with estimated gains. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
