A/B Test Significance Calculator
Free CalculatorEnter visitors and conversions for each variant to see the statistical confidence, uplift and conversion rates β instantly and privately.
100% private
Runs in your browser β no numbers leave your device.
Your test data
People who saw the control (A).
How many of them converted.
People who saw the variation (B).
How many of them converted.
Statistical confidence
95.8%
The chance the difference is real, not noise (two-tailed). 95% is the usual bar to call a winner; below 90% keep testing.
Relative uplift (B vs A)
30.0%
How much B changes the conversion rate versus A.
Conversion rate A
5.00%
Control conversion rate.
Conversion rate B
6.50%
Variation conversion rate.
How it works
Enter variant A
Add A's visitors and conversions.
Enter variant B
Add B's visitors and conversions.
Read the confidence
See the two-tailed statistical confidence update live.
Decide
At 95%+ you can call a winner; below that, keep the test running.
Test screenshots that actually move the needle
Reverze generates A/B screenshot variants so you always have a stronger version to test.
How does an A/B test significance calculator work?
An A/B test significance calculator tells you whether the difference between two variants is real or just random noise. It runs a two-proportion z-test on your conversion data: it compares each variant's conversion rate, estimates the standard error from the pooled rate, and converts the resulting z-score into a confidence level. The higher the confidence, the less likely the gap happened by chance.
The industry convention is to require 95% confidence (a 5% significance level) before declaring a winner β that means there is only a 1-in-20 chance the result is a fluke. If your confidence is below 90%, the test is inconclusive: gather more data or run it longer. Very small sample sizes almost never reach significance, which is why big, bold creative changes β like the screenshots Reverze rebuilds β are easier to prove than tiny tweaks.