Why Is My Website Slow? Complete Diagnosis Guide

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Is Your Site Actually Slow?

Before diving into fixes, let's confirm the problem and understand it.

Test Your Site

Run these tests:

1. PageSpeed Insights - Google's official tool. Shows Core Web Vitals and specific recommendations.

2. GTmetrix - Detailed waterfall charts showing exactly what's loading and when.

3. WebPageTest - Advanced testing from multiple locations with video recording.

What the scores mean:

• 90-100: Excellent
• 50-89: Needs improvement
• 0-49: Poor (significant issues)

Key Metrics to Check

Metric	Good	Needs Work	Poor
Largest Contentful Paint (LCP)	Under 2.5s	2.5-4s	Over 4s
Time to First Byte (TTFB)	Under 200ms	200-500ms	Over 500ms
Total Page Size	Under 2MB	2-5MB	Over 5MB
Number of Requests	Under 50	50-100	Over 100

The Most Common Causes (and Fixes)

1. Unoptimized Images (Most Common)

Symptoms:

• Large page size (>2MB)
• PageSpeed shows "Properly size images" or "Serve images in modern formats"
• Waterfall shows images taking seconds to load

Diagnosis: Look at your page weight breakdown. If images are >50% of total size, this is your issue.

Fixes:

• Compress images before uploading (use TinyPNG, Squoosh)
• Use WebP format (30-50% smaller than JPEG)
• Resize images to display size (don't use a 4000px image displayed at 400px)
• Lazy load images below the fold
• Use responsive images (srcset) for different screen sizes

WordPress plugins: ShortPixel, Imagify, Smush

2. Slow Hosting / High TTFB

Symptoms:

• Time to First Byte (TTFB) over 500ms
• Site is slow even with minimal content
• Slow in the morning, faster at night (shared hosting overload)

Diagnosis: GTmetrix shows TTFB clearly. If your server takes 1+ second just to respond before sending any content, hosting is the bottleneck.

Fixes:

• Enable server-side caching (reduces processing time)
• Upgrade hosting tier (more resources = faster response)
• Switch to faster hosting (if your host is genuinely slow)
• Use a CDN (serves cached content from edge locations)

For WordPress: Consider managed WordPress hosting (Kinsta, WP Engine, Cloudways)

3. Too Much JavaScript

Symptoms:

• PageSpeed shows "Reduce JavaScript execution time"
• Long "Main Thread Work" in performance audits
• Site feels slow/unresponsive even after visual load

Diagnosis: Check the number of JS files and total JS size in GTmetrix. Over 500KB of JavaScript is concerning; over 1MB is problematic.

Fixes:

• Remove unused plugins (each adds JavaScript)
• Defer non-critical JavaScript
• Eliminate render-blocking resources
• Consider lighter alternatives to heavy libraries

4. Too Many Plugins/Apps

Symptoms:

• Lots of HTTP requests (100+)
• Multiple third-party scripts loading
• PageSpeed shows many "third-party" issues

Diagnosis: Look at the waterfall chart. Are there dozens of requests to various domains? Each plugin/app adds code and external requests.

Fixes:

• Audit every plugin - Do you actually use it?
• Remove deactivated plugins (they can still load code)
• Consolidate plugins - One multi-purpose plugin vs. five single-purpose ones
• Check plugin performance impact - Use Query Monitor (WordPress) to see which plugins slow things down

5. No Caching

Symptoms:

• Every page load is equally slow
• Server resources spike on each request
• No "cache-control" headers in response

Diagnosis: Check response headers for caching directives. Load the page twice—if it's not faster the second time (with empty browser cache), server caching isn't working.

Fixes:

• Enable browser caching (cache-control headers)
• Enable server-side caching (page caching)
• Use a caching plugin (WP Rocket, W3 Total Cache, LiteSpeed Cache)
• Enable object caching for dynamic sites (Redis, Memcached)

6. No CDN

Symptoms:

• Site is fast locally, slow for distant visitors
• All requests go to single origin server
• High latency for users in other countries/regions

Diagnosis: Test from multiple locations using WebPageTest or GTmetrix. If TTFB varies significantly by location, you need a CDN.

Fixes:

• Add a CDN (Cloudflare free tier is a great start)
• Configure CDN caching rules properly
• Enable full page caching at CDN edge if possible

7. External Scripts (Ads, Analytics, Chat Widgets)

Symptoms:

• PageSpeed calls out specific third-party scripts
• Waterfall shows slow external resources
• Site loads fast initially, then slows down

Diagnosis: Look for scripts from domains you don't control. Each third-party script is a potential performance killer.

Fixes:

• Remove what you don't need (that Facebook pixel you never use...)
• Load scripts asynchronously when possible
• Delay non-essential scripts until after page load
• Self-host scripts when allowed and practical (fonts, some analytics)

Quick Wins Checklist

If you need fast improvements, tackle these first:

• Compress all images
• Enable caching plugin
• Set up free Cloudflare CDN
• Remove unused plugins
• Defer non-critical JavaScript
• Optimize your largest images (hero, featured)
• Minify CSS and JavaScript

When to Consider New Hosting

Upgrade hosting if:

• TTFB is consistently over 500ms despite caching
• You've optimized everything else
• Traffic has grown beyond your plan's resources
• Your current host has frequent downtime
• Support is unhelpful with performance issues

Good hosting options:

• Budget: SiteGround, Cloudways (DigitalOcean)
• Managed WordPress: Kinsta, WP Engine, Flywheel
• Performance-focused: Cloudflare Pages, Vercel, Netlify (for static/JAMstack)

Still Slow? Deep Debugging

If basic optimizations don't help:

1. Check database - Large, unoptimized databases slow WordPress significantly
2. Audit theme - Premium themes often include unused features
3. Check for malware - Malicious code can consume resources
4. Review server configuration - PHP version, memory limits, OPcache
5. Consider hiring help - Sometimes an expert can spot issues you miss

Speed optimization often has diminishing returns. Getting from 10s to 3s is usually straightforward. Getting from 3s to 1s requires more expertise.

Detailed Performance Analysis

Understanding Waterfall Charts

What they show:

• Each resource loading timeline
• Blocking resources
• Parallel vs sequential loading
• DNS lookup times
• Connection establishment
• Actual download time

How to read:

• Horizontal bars = time to load
• Red sections = blocking resources
• Gaps = waiting/idle time
• Stacked bars = sequential loading

What to look for:

• Long DNS lookups (switch DNS provider)
• Slow TTFB (hosting issue)
• Large file sizes (optimize)
• Many sequential requests (enable parallel loading)

Core Web Vitals Deep Dive

Largest Contentful Paint (LCP):

• Measures perceived load speed
• Target: Under 2.5 seconds
• Affected by: Server response, render-blocking resources, image loading

First Input Delay (FID):

• Measures interactivity
• Target: Under 100 milliseconds
• Affected by: JavaScript execution, main thread blocking

Cumulative Layout Shift (CLS):

• Measures visual stability
• Target: Under 0.1
• Affected by: Images without dimensions, dynamic content, fonts

Mobile-Specific Issues

Why Mobile Is Slower

Common factors:

• Slower network connections
• Less powerful devices
• Mobile-specific rendering
• Touch event delays
• Mobile browser limitations

Mobile optimization:

• Smaller images for mobile
• Touch-friendly interactions
• Reduced JavaScript
• Mobile-first design
• AMP (if appropriate)

Testing Mobile Performance

Tools:

• PageSpeed Insights (mobile tab)
• Chrome DevTools mobile emulation
• Real device testing
• WebPageTest mobile view

Mobile-specific checks:

• Image sizes on mobile
• JavaScript execution time
• Touch response time
• Mobile network simulation

Advanced Optimization Techniques

Database Optimization

WordPress database issues:

• Post revisions (clean up)
• Spam comments (delete)
• Transients (clean expired)
• Autoloaded options (reduce)

Optimization plugins:

• WP-Optimize
• Advanced Database Cleaner
• WP-Sweep

Manual optimization:

• Regular database cleanup
• Optimize tables
• Remove unused data
• Limit post revisions

Server Configuration

PHP optimization:

• Use PHP 8.0+ (faster than 7.x)
• Enable OPcache
• Increase memory limit
• Optimize PHP-FPM settings

Server-level caching:

• Object caching (Redis/Memcached)
• Page caching (Varnish/Nginx)
• Database query caching
• Opcode caching

Code Optimization

Minification:

• Minify CSS
• Minify JavaScript
• Remove comments
• Compress code

Concatenation:

• Combine CSS files
• Combine JavaScript files
• Reduce HTTP requests
• Use HTTP/2 (enables parallel loading)

Monitoring and Maintenance

Ongoing Performance Monitoring

What to monitor:

• Page load times
• Core Web Vitals scores
• Error rates
• Resource usage
• User experience metrics

Tools:

• Google Search Console
• Google Analytics
• Real User Monitoring (RUM)
• Synthetic monitoring
• Hosting provider metrics

Regular Maintenance

Weekly:

• Check performance scores
• Review error logs
• Monitor resource usage
• Test critical pages

Monthly:

• Full performance audit
• Review and optimize images
• Clean up database
• Update plugins/themes
• Review caching effectiveness

When DIY Isn't Enough

Signs You Need Professional Help

Consider hiring if:

• You've tried everything and it's still slow
• Performance is business-critical
• You lack technical expertise
• Server configuration is complex
• You need ongoing optimization

What professionals can do:

• Deep performance audits
• Server configuration optimization
• Custom caching solutions
• Code optimization
• Ongoing monitoring and maintenance

Conclusion

Slow website performance is frustrating, but most issues are fixable with systematic diagnosis and optimization. Start with quick wins, then tackle deeper issues.

Key takeaways:

• Test first to identify specific problems
• Images and hosting are most common causes
• Quick wins can make significant improvements
• Monitor performance continuously
• Consider professional help for complex issues

The bottom line: Most slow websites can be significantly improved with basic optimizations. Focus on images, caching, and hosting first. Advanced optimizations can come later if needed.

For more on performance, check out our Core Web Vitals guide or learn about website hosting.