A/B Test Calculator
Enter visitors and conversions for each variant to see conversion rates, relative lift, a two-proportion z-test and whether the result is significant.
Variant A — control
Variant B — test
Significant: B beats A at 95% confidence
A difference this large would happen by chance only 0.0306 of the time (p-value) if the variants truly performed the same.
Conversion A
5.20%
520 / 10,000
Conversion B
5.90%
590 / 10,000
Relative lift
+13.46%
p-value
0.0306
z = 2.162
95% interval for the difference in conversion rate (B − A): 0.07% to 1.33%. If it includes 0%, the test hasn't shown a real difference.
How to use the A/B Test Calculator
- 1Enter visitors and conversions for variant A (control) and variant B.
- 2Pick a confidence level — 95% is standard.
- 3Read the verdict, lift, p-value and the confidence interval for the difference.
Frequently asked questions
How does this A/B test calculator work?
It runs a two-sided, two-proportion z-test with a pooled standard error, and gives a confidence interval for the difference in conversion rates.
What does statistically significant mean?
That a difference as large as the one observed would be unlikely if the variants truly performed the same. At 95% confidence, the p-value must be below 0.05.
Can I stop my test as soon as it's significant?
No. Checking repeatedly and stopping at the first significant result inflates false positives. Decide the sample size in advance with a sample size calculator and run the test to the end.
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