ABWex is a free A/B test calculator that supports both frequentist and Bayesian statistical analysis. It runs entirely in your browser with no data sent to any server.
Frequentist Mode uses the two-proportion Z-test to calculate p-values, confidence intervals, and relative improvement. The exact formula is shown for every calculation, and results are color-coded by significance level.
Bayesian Mode uses a Beta-Binomial model to compute P(B beats A) via numerical integration (Simpson's rule for deterministic results). It displays overlapping Beta distribution curves as SVG paths and calculates expected loss if you choose the wrong variant.
Multi-Variant Comparison supports up to 4 variants (A/B/C/D). It compares all pairs, highlights the winner, and in Bayesian mode shows the probability that each variant is best.
Revenue Impact Calculator takes your average revenue per conversion and monthly traffic to project monthly and annual revenue changes.
Sample Size Pre-Calculator computes required sample size based on baseline rate, minimum detectable effect, power, and significance level. It includes a duration estimate based on your daily traffic and a power curve visualization.
The statistical calculations use standard formulas from the statistics literature. The normal CDF uses the Abramowitz and Stegun rational approximation (error less than 7.5 times 10 to the minus 8). The Beta distribution uses log-gamma via Lanczos approximation for numerical stability. All formulas are visible in the source code and displayed in the UI.
Built by Michael Lip — Solo developer with 10+ years experience. 140+ PRs merged into open source projects including Google Chrome and Axios. $400K+ earned on Upwork with 100% Job Success. Creator of 20+ Chrome extensions.
ABWex is part of the Zovo developer tools collection. Other tools include Enhio for content enhancement, Krzen for image compression, and EpochPilot for ML training management.