Free 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 three to four 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 →StatisticsMargin of error (FPC)
Survey margin of error with the finite population correction, corrected and explained.
Open tool →StatisticsSample size: one proportion
Cochran sample size with FPC, design effect, and response-rate adjustment.
Open tool →StatisticsCluster sample size
How many clusters to sample given the intraclass correlation.
Open tool →StatisticsStratum allocation
Allocate completes across strata with priority weights and oversampling.
Open tool →StatisticsDesign weights
Nonresponse-adjusted weights with ready-to-paste SPSS syntax.
Open tool →FinanceCost basis: new purchase
Your new average cost per share after buying more of a position.
Open tool →FinanceShares for target cost basis
How many shares to buy so your cost basis hits your target.
Open tool →FinanceRecurring investment projector
Project contributions from a weekly investing schedule over any date range.
Open tool →FinancePortfolio rebalance
Dollar targets and buy/sell amounts to restore target weights.
Open tool →The Investor Stats Cheat Sheet
A free three-page PDF: breakeven win rates, stop-loss sizing, volatility drag, reverse valuation, and how to tell a real track record from noise. Plus new tools as they ship.