Google's own research shows: 53% of mobile visitors leave a website that takes longer than 3 seconds to load. For every extra second of load time your conversion rate drops by 7% on average. For a webshop doing €50,000 a month, that's €3,500 per second of delay. Every month.
The biggest speed killers
Theme bloat is the number one cause. Many Shopify themes load 15-20 apps on every page, even when they're not visible. Review widgets, upsell popups, tracking pixels, they stack up. Start with an audit: which apps do you really need? Remove the rest. Not deactivate, but actually remove. Deactivated apps often leave behind CSS and JavaScript.
Images are the second culprit. Use WebP format, lazy loading, and make sure product photos aren't wider than 1200px. Shopify's CDN compresses automatically, but only if you supply the right formats. A product page with 8 photos of 3MB each loads unacceptably slowly.
Improving Core Web Vitals
Focus on three metrics: LCP (Largest Contentful Paint) under 2.5 seconds, CLS (Cumulative Layout Shift) under 0.1, and INP (Interaction to Next Paint) under 200ms. Measure this with Google PageSpeed Insights. Our Shopify CRO approach always starts with a speed audit, it's the first and easiest win you can get.