The verdict in three sentences
A 4.2 s LCP drags down both your conversions and your Google rankings, especially now that INP has replaced FID as the interactivity metric. In 2026, count on 700 to 2,500 EUR for the audit and 2,500 to 8,000 EUR for the project (AVIF images, CDN, lazy-load, front-end rework). Hitting LCP < 2.5 s / INP < 200 ms typically returns +7 to +15 % conversion and +5 to +12 positions.
What web performance costs in 2026
Core Web Vitals aren't a luxury: they're ranking signals and a direct conversion lever. Here are the 2026 ranges for a B2B site.
| Service | 2026 range | Deliverable |
|---|---|---|
| Performance audit | 700 - 2,500 EUR | Lighthouse + CrUX report + plan |
| Image optimization (AVIF/WebP) | 800 - 2,000 EUR | Conversion, srcset, compression |
| CDN + cache setup | 600 - 1,800 EUR | CDN, cache-control, edge |
| Critical front rework | 2,000 - 4,500 EUR | Critical CSS, defer JS, hydration |
| Lazy-load + preload | 400 - 1,200 EUR | Resource prioritization |
| Full project | 2,500 - 8,000 EUR | All of the above, LCP < 2.5 s |
Budget climbs mostly when the front-end is heavy (bloated WordPress theme, uncontrolled JS) and you must rework hydration or move to partial rendering.
Before / after: Lighthouse score and business impact
Prioritization is done by effort/impact ratio. Here's a typical project taking a Lighthouse score from 48 to 92, with the effect on metrics.
| Metric | Before | After | Main action |
|---|---|---|---|
| Lighthouse score | 48 | 92 | Full project |
| LCP | 4.2 s | 2.1 s | AVIF + preload + CDN |
| INP | 340 ms | 160 ms | Defer JS, task splitting |
| CLS | 0.28 | 0.04 | Reserved media dimensions |
| Conversion rate | 1.8 % | 2.1 % | +17 % relative |
| Average position | 12.4 | 6.8 | +5.6 positions |
As a rule, every second of LCP gained under the 2.5 s threshold translates to +3 to +7 % conversion, and the SEO effect materializes in 4 to 10 weeks after the CrUX field data updates.
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Mini case study
Sophie is e-marketing director of a B2B industrial-equipment distributor. Her site shows a 4.2 s LCP and a 1.8 % conversion rate over 42,000 visits/month. She invests 1,800 EUR in the audit and 6,200 EUR in the project, i.e. 8,000 EUR. After reaching LCP 2.1 s and INP 160 ms, conversion rises to 2.1 %: on an average ticket of 620 EUR, that adds ~127 extra orders/month, i.e. ~78,000 EUR of annual revenue. The project pays back in under 6 weeks, before counting the organic ranking gains.
FAQ
What changed with INP in 2026? INP (Interaction to Next Paint) measures real responsiveness across the whole session, not just the first click. A JS-heavy interactive site can have a good LCP but an INP > 300 ms that penalizes it.
How long does a performance project take? Count 2 to 5 weeks for a full project, depending on technical debt. The audit takes 3 to 7 business days.
Is the SEO gain guaranteed? No, but Core Web Vitals are a confirmed signal. In practice, moving under the thresholds brings +5 to +12 positions on queries where you were close to the top 10.
Do I need to rebuild everything? Rarely. 70 % of gains come from images, CDN and JS deferral. A full front rebuild is only justified if the theme is structurally heavy.
How do I measure real impact? Track CrUX field data (real user data) over 28 days, not just Lighthouse lab data. Cross-reference with conversion rate and average position in Search Console.
Let's scope your project. Send us your URL and current scores: we'll price the audit, the priority project and the expected conversion gain. 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.
