Bayesian A/B Test Calculator

Compare two conversion-rate variants with Beta(1,1) priors. See each posterior mean, the probability that the variant beats control, and its expected lift.

Control

Variant

98.9%
Probability variant wins
10.0%
Expected relative lift
10.01%
Control posterior mean
11.01%
Variant posterior mean

The probability uses a moment-matched normal comparison of the two Beta posteriors. Treat it as evidence, not a stopping rule: decide your decision threshold and test horizon before looking.

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