A/B Test Calculator
Real statistics, not a verdict machine. Enter the visitors and conversions for each variant to get the conversion rates, the relative lift, a p-value and a confidence interval — plus the sample size you needed up front, which is the number most tests are stopped before reaching.
Free, runs entirely in your browser. No account, no usage limits, and nothing you type is uploaded.
Questions
What does the p-value mean?
The probability of seeing a difference this large if the variants were actually identical. Below 0.05 is the usual bar — it does not tell you the size of the win, only that it is unlikely to be noise.
Why not stop as soon as it goes green?
Because significance fluctuates as data arrives, and a test checked repeatedly will cross 0.05 by chance eventually. Decide the sample size first, then look.
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