Core Web Vitals in 2026: why a slow mobile site costs you 30% of revenue
Back to ArchiveA senior frontend engineer's 2026 deep-dive on Core Web Vitals (LCP, INP, CLS). Why mobile-LCP above 2.5s costs Moroccan SMEs 20-35% of mobile revenue. The five interventions that move the number.
TL;DR — A mobile site with LCP above 2.5 seconds in 2026 leaves 20-35% of potential revenue on the table. The five interventions that move the number: image pipeline, JS budget, font loading, third-party scripts, and server response time.
What are Core Web Vitals in 2026?
- LCP — Largest Contentful Paint. Good: <2.5s. Poor: >4s.
- INP — Interaction to Next Paint. Good: <200ms. Poor: >500ms.
- CLS — Cumulative Layout Shift. Good: <0.1. Poor: >0.25.
How much does slow mobile cost?
Every 1 second cut from mobile LCP corresponds to a 7-12% lift in conversion. A site at 3.5s LCP dropping to 0.9s typically sees a 22-35% conversion lift.
The five interventions
(1) Image pipeline. AVIF + WebP. Impact: -1.0 to -2.5 seconds.
(2) JS budget. Cap at 80-120KB gzipped. Large LCP and INP impact.
(3) Font loading. Self-host, preload, font-display: swap. Impact: -0.3 to -0.8s.
(4) Third-party scripts. Audit, defer, or remove. Large impact.
(5) Server response time. Get TTFB under 200ms.
What we recommend at BidayaLab
We do this as a 2-4 week engagement with a written commitment to LCP <1.2s and INP <200ms. Free 30-minute audit.