The verdict in three sentences
A slow B2B site (LCP at 4.5 s) hurts both SEO and conversion rate. In 2026, a performance audit costs EUR 1 200-3 000 and the optimisation project EUR 4 000-12 000 depending on the stack. Target: LCP < 2.5 s, INP < 200 ms, CLS < 0.1, for a realistic 15-30 % conversion lift and a better average position.
The three metrics that matter in 2026
Google evaluates experience via three Core Web Vitals. Here are the official thresholds and the business impact of exceeding them.
| Metric | "Good" threshold | What it measures | Effect if poor |
|---|---|---|---|
| LCP | < 2.5 s | Largest element load | Bounce +, SEO - |
| INP | < 200 ms | Interaction responsiveness | Frustration, form abandonment |
| CLS | < 0.1 | Visual stability | Misclicks, distrust |
Moving from red to green on all three is the foundation of an optimisation. On a B2B site, INP is often the weak point due to third-party scripts (chat, analytics, tag manager).
Project cost and expected gains
Here is a typical before/after on a B2B lead-generation site, with optimisation items and their cost.
| Item | Before | After | 2026 cost (EUR) |
|---|---|---|---|
| LCP (hero image + fonts) | 4.5 s | 2.1 s | 1 500 - 3 500 |
| INP (third-party scripts, JS) | 320 ms | 150 ms | 1 200 - 3 000 |
| CLS (layout, ads) | 0.25 | 0.04 | 600 - 1 500 |
| WebP/AVIF images + lazy | -60 % weight | optimised | 800 - 2 000 |
| CDN + cache + compression | - | enabled | 500 - 2 000 |
Realistic total budget: EUR 4 600-12 000 for a full project. On a site generating 200 leads/month, a +20 % gain means 40 extra leads/month.
Mini case study
Thomas, marketing director at a B2B software vendor in Nantes, has a site with LCP 4.5 s and a 2.4 % conversion rate on 25 000 visits/month, i.e. 600 leads/month. He invests EUR 8 000 in a performance project. After 6 weeks, LCP drops to 2.1 s and conversion rises to 2.9 % (+21 %), i.e. 125 extra leads/month. With an average acquisition cost of EUR 35/lead via Ads, those free leads are worth EUR 4 375/month: the investment pays back in under two months.
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FAQ
How long does a Core Web Vitals project take?
Between 3 and 8 weeks depending on complexity. The audit takes 1 week, optimisation 2 to 6 weeks, plus a measurement window on field data (CrUX) which reports over 28 days.
Do I need to rebuild the whole site to improve CWV?
Rarely. We first optimise the existing site (images, fonts, scripts, cache). A rebuild is only justified if the stack is obsolete or the code unmanageable.
Do Core Web Vitals really influence SEO in 2026?
Yes, they are a confirmed ranking signal, especially between otherwise equal positions. Their impact is amplified on mobile, where most B2B traffic now arrives.
How do I measure INP correctly?
INP is measured on real field data via Search Console and CrUX, not just in a Lighthouse lab. We instrument the site to track INP per page and per device.
Can a WordPress site reach green?
Yes, with the right work on the theme, plugins and cache. If WordPress is too heavy, a migration to a headless stack (Next.js) is an option we price separately.
Let's scope your project. Send us your URL and conversion goals: we run a pre-diagnosis and price an audit plus project matched to your stack. 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.
