Free Calculator
A/B Test Calculator
Calculate statistical significance for your A/B tests or plan sample sizes for new experiments.
Test Results
Control (A)
Variant (B)
Enter your test results to analyze significance.
Understanding A/B Testing Statistics
Statistical Significance
A result is significant when there's less than 5% probability it happened by chance (p < 0.05). This means 95% confidence.
Sample Size
Smaller effects require larger samples to detect. A 1% improvement needs more data than a 20% improvement.
When to Stop
Run tests until you reach significance OR your planned sample size. Stopping early or peeking increases false positives.
Minimum Detectable Effect
The smallest change worth detecting. If a 5% improvement isn't meaningful to your business, plan for detecting 10%+.