Posterior mean A
0%
Bayesian A/B Test Calculator
Compare two conversion variants with posterior probability under a visible beta prior.
At a glance
- Computes
- P(B beats A), median lift, and a credible interval, by Monte Carlo.
- You supply
- Conversions and visitors for both variants, plus the beta prior you choose.
- Use when
- You want the probability that one variant is better, stated directly.
- Not for
- Reporting a frequentist p-value or a significance verdict. A/B Test Calculator
P(B beats A)
Enter counts
Uses a visible beta prior.
Posterior mean B
0%
Posterior density against Conversion rate
Posterior density against Lift, B minus A
| Metric | Value |
|---|
posterior = Beta(alpha + conversions, beta + visitors - conversions)
How?
How this is calculated
Each conversion rate has a beta prior and binomial likelihood. The calculator samples paired posterior rates with a deterministic seed, reports the share where B is greater than A, and uses empirical quantiles for the difference interval.
Formula: posterior = Beta(alpha + conversions, beta + visitors - conversions)
Sources
- Evan Miller Formulas for Bayesian A/B Testing. Evan Miller. Retrieved .
- Bayesian Data Analysis. Columbia University. Retrieved .
Method last reviewed