Why Is My Website So Slow? 7 Common Reasons

A slow website loses visitors, sales, and Google ranking. The good news: in most projects I am hired to fix, the slowness comes from the same handful of causes, and each one has a known fix.

How to diagnose before you fix

Never guess. Run your site through PageSpeed Insights (free) and open your browser DevTools Network tab. Sort requests by size and by time. In two minutes you will know whether your problem is images, scripts, or the server.

1. Oversized images

The number one cause. A 4000px photo squeezed into a 400px card still downloads all 5 MB. Serve properly sized images in modern formats:

<!-- Plain HTML: let the browser pick the right size -->
<img
  src="/products/chair-800.webp"
  srcset="/products/chair-400.webp 400w, /products/chair-800.webp 800w"
  sizes="(max-width: 600px) 100vw, 400px"
  loading="lazy"
  alt="Wooden chair"
/>

// Next.js: the Image component does this automatically
import Image from 'next/image'
<Image src="/products/chair.webp" width={400} height={300} alt="Wooden chair" />

2. No caching

Without cache headers, every visit re-downloads everything and every request rebuilds the page. Static assets should be cached for a year, pages according to how often they change:

# Nginx: cache static assets aggressively
location ~* \.(webp|png|jpg|css|js|woff2)$ {
  expires 1y;
  add_header Cache-Control "public, immutable";
}

3. Render-blocking scripts

Scripts in the head without defer stop the page from painting until they download and run. Analytics, chat widgets, and pixels are the usual offenders:

<!-- Bad: blocks rendering -->
<script src="https://widget.example.com/chat.js"></script>

<!-- Good: loads after the page paints -->
<script src="https://widget.example.com/chat.js" defer></script>

4 to 7: the rest of the list

• Overloaded shared hosting: if the server answers slowly (high TTFB in DevTools), no frontend fix helps. Move to better hosting
• Slow database queries: pages that assemble data from many unindexed queries. Add indexes and cache the results
• Too many plugins or third-party scripts: every one adds requests. Audit and remove
• No CDN: visitors far from your server wait for every byte. A CDN serves assets from a location near them

A realistic target

Under 3 seconds on mobile is healthy, under 1 second feels instant. Fixing images and caching alone gets most sites more than halfway there. If the site is still slow after that, the problem is in the code or database, and that is worth a developer looking at it.