Estimate a full and half Kelly fraction from win probability and payoff odds.
It makes the prices, cash flows, rates, time periods, weights, and model conventions explicit so you can inspect an entered scenario without hidden live-market assumptions.
Calculation structure
Follow the stated model and units
Kelly fraction = win probability − loss probability ÷ win-to-loss payoff ratio.
Visual explanation
See how the inputs become the result
Capital and cash flowstime and rate→entered modelScenario resultChanging one assumption changes the model—not the marketKelly fraction = win probability − loss probability ÷ win-to-loss payoff ratio.
Read the estimate correctly
Use the result within its boundaries
A 55% win probability and 1.5 payoff ratio produce a 25% full Kelly fraction.
Kelly is highly sensitive to uncertain probabilities and payoff estimates. A positive result does not make an investment suitable or limit losses.
Quick guide
How to use this calculator
Enter the exposure, market, accounting, probability, rate, or risk assumptions named by the fields.
Use consistent currencies, periods, share units, and percentage conventions.
Interpret the output only within the displayed model and limitations.
Calculation method
Calculation method
Kelly fraction = win probability − loss probability ÷ win-to-loss payoff ratio.
Fixed decimal scalar arithmetic remains exact until display. Square-root and compound projections are explicitly approximate and reject non-finite results.
Worked example
Worked example
A 55% win probability and 1.5 payoff ratio produce a 25% full Kelly fraction.
Kelly fraction = win probability − loss probability ÷ win-to-loss payoff ratio.
Supported inputs
Precision and limits
Visible input limits
Fixed decimals accept 30 digits and 12 decimal places, with absolute values capped at 1e12 per input and general rates capped at 1000%. Formula-specific shares and probability limits are validated separately.
International scope
No currency, exchange, broker, live security data, accounting standard, tax jurisdiction, contract specification, or regulatory disclosure is selected automatically.
Decision boundary
Outputs are arithmetic scenarios, not forecasts, advice, suitability assessments, trading signals, fair-value opinions, risk guarantees, or recommendations.
Calculator-specific assumptions
Kelly is highly sensitive to uncertain probabilities and payoff estimates. A positive result does not make an investment suitable or limit losses.
