A/B Test Calculator

Yes. The calculator is completely free, with no sign-up and no usage limits. Run as many significance, sample size and duration calculations as you need.

Yes. Every calculation runs entirely in your browser. The visitors and conversions you enter are never uploaded or stored on a server.

The frequentist p-value is the probability of seeing a difference this large if the variants were actually identical. The Bayesian figure is the probability that the winning variant is genuinely better, which is often easier to act on.

A result is significant when the p-value falls below your chosen threshold, for example 0.05 at 95% confidence. It means the observed lift is unlikely to be down to random chance, not that the lift is large or permanent.

Both use your baseline conversion rate, the minimum detectable effect, the confidence level and the statistical power to find the visitors per variant needed. Duration simply divides that target by your daily traffic.

Run the test until you reach the calculated sample size, and cover full weekly cycles to capture weekday and weekend behaviour. Avoid stopping early or peeking at results, as that inflates false positives.