The verdict in three sentences
Core Web Vitals (LCP, INP, CLS) are a Google ranking factor and a direct conversion lever, especially on mobile. Hitting the 2026 targets (LCP < 2.5s, INP < 200ms, CLS < 0.1) via WebP/AVIF images, lazy loading and edge CDN costs between 2,500 and 7,000 EUR excl. tax. The measured conversion gain ranges from +8 to +20%, paying back the investment within months for a lead-generating site.
Targets and their 2026 impact
Google defines three main metrics. An optimised site passes the "good" threshold on mobile, an increasingly decisive condition for local SEO in London.
| Metric | "Good" target 2026 | What it measures |
|---|---|---|
| LCP | < 2.5s | Speed to render main content |
| INP | < 200ms | Responsiveness to interactions |
| CLS | < 0.1 | Visual stability (no jump) |
| TTFB | < 800ms | Server response time |
| Mobile page weight | < 1.5 MB | Load on mobile networks |
On an average 4G connection, every second shaved off load time noticeably cuts bounce rate and lifts quote requests.
Prioritising by effort and impact
Not all optimisations have the same return. Here is how to prioritise in 2026, from quick wins to heavier work.
| Lever | Effort | Impact | Indicative cost EUR |
|---|---|---|---|
| WebP/AVIF image compression | Low | High (LCP) | 300 - 750 |
| Image/video lazy loading | Low | Medium | 225 - 600 |
| Edge CDN | Medium | High (TTFB, LCP) | 450 - 1,200 |
| JS/CSS reduction | Medium | High (INP) | 600 - 1,800 |
| Server caching | Low | Medium | 225 - 750 |
| Targeted technical rebuild | High | Very high | 1,500 - 3,800 |
Start with images and the CDN: they offer the best effort-to-impact ratio for a slow site.
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Mini case study
Sarah, digital manager at a B2B services SME in London, runs a site whose mobile LCP hits 4.8s and whose form conversion caps at 1.4%. She invests 4,800 EUR in optimisation: AVIF compression, lazy loading, edge CDN and JavaScript reduction. LCP drops to 2.1s, INP to 160ms. Conversion climbs to 1.7%, i.e. +21% more quote requests. On 3,500 visitors/month, that's around ten extra leads monthly, paying back the optimisation in under 4 months.
FAQ
Do Core Web Vitals really affect SEO? Yes. They are part of Google's page experience signals. With equivalent content, a site passing the "good" thresholds on mobile is favoured, especially in local search.
What's the most profitable lever? WebP/AVIF image compression: low effort, high impact on LCP, cost of 300 to 750 EUR. It's almost always the first project to launch.
Why optimise for mobile networks? A large share of traffic comes via mobile on variable networks. A site under 1.5 MB loads fast even on average 4G, whereas a 4 MB site drives visitors away.
How much does a full optimisation cost? In 2026, budget 2,500 to 7,000 EUR excl. tax depending on the starting state. A badly degraded site may need a targeted technical rebuild beyond this budget.
How soon do results show? Performance gains are immediate after deployment. SEO impact (rankings) is measured over 4 to 8 weeks, the time Google needs to re-evaluate pages.
Let's scope your project. Send us your site URL and current scores: we'll audit Core Web Vitals and cost an optimisation plan prioritised by effort/impact. 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.
