Tools
Small calculators I reach for when planning experiments, reading the results, and sizing what I put behind them. No sign up, no data leaves the page.
A/B test sample size
How many visitors per arm you need to detect the lift you care about, and how long that takes at your traffic.
Two proportion test · Power, significance, one or two sided
A/B test significance
Paste in visitors and conversions to get the frequentist p-value and confidence interval alongside the Bayesian posterior.
Pooled z-test · Beta-binomial posterior, side by side
Kelly criterion
How much of the bankroll to stake on an edge, and what betting more or less than that costs you in growth.
Optimal stake · Fractional Kelly, growth curve, drawdown risk
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