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Most A/B tests are declared finished too early, when the difference between versions is still within the range of pure chance. This calculator runs a proper two-proportion test on your two versions: it works out each conversion rate, the uplift between them, and a z-score with a p-value that tells you whether the gap is statistically significant at the 95% level. Its verdicts are deliberately cautious — small samples are flagged as hints, not results, and significance is separated from practical importance.
Most A/B tests are stopped too early, when the result is still coin-flip noise. Enter the visitors and conversions for each version and this calculator runs a two-proportion test to tell you honestly whether the difference is real.
Until each version accumulates enough conversions — often 100 or more per side to detect a meaningful lift, more for smaller effects. Decide the minimum lift worth shipping before you start, then let the test run until the calculator stops saying 'not enough data'.
It means a difference this size would arise by chance less than one time in twenty if the versions truly performed the same. It does not mean the difference is large, profitable, or certain — just that it is probably real.
Almost never. Early results are dominated by noise — one version simply caught an easier audience first. Ignore results until the sample is large enough; the calculator will tell you when it is.
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