The verdict in three sentences
A Berlin e-commerce site with a 4.2 s LCP loses sales with every millisecond. In 2026, a full performance project costs 4,000 to 9,000 EUR (including a 1,200 EUR audit) and takes 3 to 5 weeks. The typical gain: LCP down to 1.8 s, INP under 200 ms, and +14 % conversion rate — each 0.8 s saved is worth roughly +7 % revenue.
What a Core Web Vitals project covers in 2026
Core Web Vitals (LCP, INP, CLS) are a Google ranking factor and, above all, a direct conversion lever. Here is the structure of a serious project and its indicative cost.
| Phase | Actions | Duration | 2026 indicative cost |
|---|---|---|---|
| Performance audit | Lab + field (CrUX), waterfall, perf budget | 3-5 days | 1,200 EUR |
| Images & media | AVIF/WebP, lazy-loading, dimensions | 1 week | 800-1,800 EUR |
| JavaScript | Code-splitting, hydration, third parties | 1-2 weeks | 1,500-3,500 EUR |
| CSS & rendering | Critical CSS, fonts, layout shift | 3-5 days | 700-1,600 EUR |
| Cache & CDN | Edge cache, ISR, Brotli compression | 3-5 days | 600-1,400 EUR |
| QA & monitoring | Testing, RUM, regression alerts | 3 days | 500-1,000 EUR |
For a mid-sized e-commerce site (5,000 to 30,000 visits/month), the realistic envelope sits around 6,500 EUR, including 3 months of monitoring.
Before / after: what performance really returns
The real argument is not the Lighthouse score but revenue. Here is a representative before/after of a successful project.
| Metric | Before | After | Business effect |
|---|---|---|---|
| LCP | 4.2 s | 1.8 s | +7 % revenue per 0.8 s saved |
| INP | 340 ms | 180 ms | Smooth navigation, fewer drop-offs |
| CLS | 0.28 | 0.04 | Fewer mis-taps on cart |
| Conversion rate | 1.6 % | 1.82 % | +14 % relative |
| Mobile bounce rate | 58 % | 46 % | -12 points |
| Pages/session | 3.1 | 4.0 | +29 % depth |
For a site doing 80,000 EUR/month, a +14 % conversion lift means roughly 11,200 EUR/month of extra revenue. The 6,500 EUR project pays for itself in under 3 weeks of operation.
Mini case study
Marc is head of e-commerce for an outdoor gear brand in Berlin, 90,000 EUR monthly sales, 1.55 % conversion. His mobile LCP peaks at 4.3 s due to a heavy carousel and 6 marketing scripts. He commissions a 6,800 EUR project over 4 weeks. After delivery, LCP drops to 1.9 s, conversion rises to 1.78 % (+15 %). On 90,000 EUR, that adds ~13,500 EUR/month. ROI is reached in 15 days; over 12 months, the project generates more than 160,000 EUR in added revenue.
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FAQ
Is a good Lighthouse score enough?
No. Lighthouse is a lab test; Google ranks on field data (CrUX). You must hit green thresholds on real visits, not just in an isolated test.
How long does a performance project take?
Between 3 and 5 weeks for a mid-sized e-commerce site. Sites heavy on third-party scripts or on a bulky CMS can require 6 to 8 weeks.
Which metric to prioritize in 2026?
LCP and INP. INP replaced FID and penalizes slow-to-respond interfaces: it is often the weak point of JavaScript-heavy e-commerce.
Do you need to rebuild the site to gain speed?
Rarely. 70 to 80 % of gains come from optimizing images, JavaScript and cache on the existing site. A rebuild is justified only if the technical base is obsolete.
Are the gains durable?
Yes, if monitored. A performance budget and regression alerts prevent every new marketing script from degrading LCP again.
Let's scope your project. Send us your URL and current Core Web Vitals (PageSpeed or Search Console), and we'll price a performance project with a conversion goal. 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.
