The verdict in three sentences
Core Web Vitals are no longer optional: they weigh on both the SEO and the conversion rate of your B2B site. The 2026 targets are sharp: LCP < 2.5 s, INP < 200 ms, CLS < 0.1 and a mobile Lighthouse score above 90. On a Berlin rebuild, budget 2,500 to 6,000 EUR for performance, repaid through 1 to 3 % conversion gained per 100 ms.
The 2026 targets and their business impact
A slow site does not just lose rankings: it loses prospects at every step of the journey. Here are the thresholds to hit and what they return.
| Metric | "Good" 2026 threshold | Impact of exceeding it |
|---|---|---|
| LCP (loading) | < 2.5 s | +100 ms = -1 to -3 % conversion |
| INP (interactivity) | < 200 ms | Perceived lag, bounce +5 to 8 % |
| CLS (visual stability) | < 0.1 | Missed clicks, mobile frustration |
| Mobile Lighthouse score | > 90 | Google credibility threshold |
| TTFB (server response) | < 600 ms | Delays the whole render |
| Total page weight | < 1.5 MB | 3G/4G: abandonment before display |
On mobile the stakes double, because most B2B traffic now arrives from smartphones on networks slower than the office fibre.
Before / after: what a performance rebuild changes
Here are the typical gains from a performance-focused rebuild, with the levers that produce them.
| Indicator | Before rebuild | After rebuild | Main lever |
|---|---|---|---|
| Page weight | 3.4 MB | 1.1 MB | WebP/AVIF (-40 % images) |
| TTFB | 950 ms | 220 ms | CDN + server cache |
| Mobile LCP | 4.8 s | 2.1 s | Lazy-load + critical preload |
| Lighthouse score | 42 | 93 | Local fonts + reduced JS |
| Conversion rate | 1.4 % | 2.3 % | Overall speed |
The most profitable levers: convert images to WebP/AVIF (-40 % weight), serve via a CDN, enable lazy-load, cache aggressively and host fonts locally rather than through an external service.
Mini case study
Sophie, e-marketing director of a software vendor in Berlin, rebuilds her marketing site (mobile Lighthouse score 42). She invests 4,200 EUR in a performance workstream. Result: LCP drops from 4.8 s to 2.1 s, score to 93, and form conversion climbs from 1.4 % to 2.3 %. On 9,000 monthly visitors that means 126 leads/month versus 81, i.e. +45 leads. At an equivalent acquisition cost, the investment pays back in under three months.
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FAQ
Is the Lighthouse score enough to judge performance?
No: Lighthouse is a lab test. Cross-reference it with field data (CrUX/Search Console) that reflects the real experience of users on their devices.
How much does performance optimisation cost in 2026?
Between 2,500 and 6,000 EUR depending on site size and starting state. A very heavy site (score < 40) needs more work on images and JavaScript.
Has INP really replaced FID?
Yes, INP has been the reference interactivity metric since 2024. Hitting under 200 ms means reducing blocking JavaScript and optimising event handlers.
Is a CDN essential?
For a site with distributed or international traffic, yes: it cuts TTFB by hundreds of milliseconds by serving content closest to the user.
What exactly links performance and SEO?
Core Web Vitals are a ranking signal. With equal content, a fast site ranks better and converts more: the dual benefit justifies the investment.
Let's scope your project. Send us the URL to audit and your conversion goals, and we will cost a performance workstream (budget, levers, expected gains) tailored to your rebuild. 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.
