Apdex (Application Performance Index) is a standardized way to measure and interpret application response times based on user experience. It provides a simple numerical score representing how satisfied users are with performance.

​
How Apdex Works

Apdex scores are based on response time thresholds:
  • Satisfied (Fast Response): Requests that complete within the target response time.
  • Tolerating (Acceptable Response): Requests that take longer but are still within an acceptable range (typically 4x the target response time).
  • Frustrated (Slow Response): Requests that exceed the tolerable threshold, indicating poor performance.
The formula for Apdex score: 
Apdex = (Satisfied Requests + (Tolerating Requests / 2)) / Total Requests
  • 1.0 = Excellent performance (all users satisfied)
  • 0.85+ = Good performance
  • 0.7 - 0.85 = Fair performance, potential for improvement
  • Below 0.7 = Poor performance, significant user frustration

​
Apdex in LoadForge

LoadForge automatically calculates Apdex scores for every test and displays them in the test results page. This helps you quickly assess whether your site or API is performing as expected.

​
Where to Find Your Apdex Score

  • Every test run result in LoadForge includes an Apdex calculation.
  • The Apdex score is displayed alongside response time statistics (P95, average) and error rates.
  • If your Apdex score is below your target, LoadForge will mark the test as failed.

​
Inside of a Run Result

Apdex report

Apdex Report in Run Results

​
On the List of Runs

Apdex report

Apdex Scores in Runs List

​
Setting Your Apdex Target

Start with a more lenient Apdex target (higher ms) and gradually decrease it as you optimize your application. This creates achievable milestones for your team.
When creating a test, you can define an Apdex Target Response Time (in milliseconds). This is the response time under which requests are considered “satisfied.”
Application TypeSuggested Apdex Target
Static Websites200ms - 500ms
APIs & Web Services300ms - 800ms
E-Commerce Sites500ms - 1000ms
Enterprise Applications1000ms - 2000ms

​
How to Improve Your Apdex Score

If your Apdex score is low, consider optimizing:
  1. Backend Performance: Reduce database query times, optimize API calls.
  2. Caching: Use caching layers (Redis, Cloudflare, etc.) to speed up response times.
  3. Scaling: Increase server capacity or use auto-scaling for high-traffic periods.
  4. Content Optimization: Minimize JavaScript execution, optimize images, and reduce page load times.
  5. CDN Usage: Distribute static content across global locations to improve response times.

​
Conclusion

Apdex provides an objective measure of performance that aligns with user experience. LoadForge integrates Apdex scoring directly into test results, making it easy to assess whether your application meets performance expectations. By setting realistic Apdex targets and monitoring test results, you can continuously improve the responsiveness and reliability of your services.

Run Results

Learn how to interpret load test results and optimize performance

Comparing Runs

Compare different test runs to track improvements over time