MaineblockFree calculators
Every tool runs entirely in your browser — your numbers never leave your device. Each one states its assumptions and interprets the result in plain English, because a number without context is how bad decisions happen.
Sample size calculator
Two-proportion sample size with power input, dropout adjustment, and subgroup warnings.
Open tool →StatisticsA/B test significance
Two-sample proportion z-test with p-value, confidence interval, and a practical-significance flag.
Open tool →StatisticsWhich test do I need?
Answer 3–4 questions and get the right statistical test for your data.
Open tool →StatisticsPower analysis (t-test)
Find the sample size you need for a two-sample t-test, with an effect-size slider.
Open tool →FinancePosition size (Kelly)
Full Kelly, half-Kelly, and quarter-Kelly with an honest drawdown warning.
Open tool →FinanceOptions payoff visualizer
See exactly what long calls, long puts, and covered calls pay at expiry.
Open tool →The Investor Stats Cheat Sheet
A free two-page PDF: expected value, Kelly sizing, Sharpe, sample-size math, and how to read a p-value without fooling yourself. Plus new tools as they ship.