Kelly Criterion Calculator
Calculate full, half and quarter Kelly allocations from your bankroll, probability and odds or binary contract costs. Compare rounded stakes, contracts and EV.
Enter your own winning-probability estimate and the offered price. Start with the hypothetical contract example or choose standard betting odds. All money amounts are USD.
Model allocation under your probability assumption. A losing settlement can lose all allocated cash.
Whole contracts are rounded down to fit the model budget. Cash includes the entered linear fee per contract. It can be less than the unrounded model budget.
Full Kelly = max(0, (p − c) ÷ (1 − c)), where p is your assumed probability and c is the break-even probability. The selected fraction scales full Kelly. Cost at or above the winning payout gives zero allocation.
Assumes a fully paid $1-or-$0 contract and linear per-contract costs paid regardless of outcome. Educational model only. Your probability may be wrong. No live prices, forecasts, order submission, portfolio sizing, taxes, rebates, fixed order fees or conditional charges.
How to use the Kelly calculator
- Enter the available bankroll and your own probability estimate for the purchased side or selection.
- Choose binary-contract pricing or standard odds, enter the price, and select full, half or quarter Kelly.
- Compare the theoretical budget with rounded allocated cash, both settlement outcomes and expected net. Recheck probability assumptions before interpreting any result.
Hypothetical example: $1,000 bankroll, 60% probability, 55-cent contracts and an assumed 1-cent fee per contract. Full Kelly is about 9.09%; quarter Kelly gives a $22.73 displayed model budget. Rounding down gives 40 contracts costing $22.40, a $17.60 winning net, a $22.40 losing cost and $1.60 EV.
Need to convert prices? Use the odds converter.Kelly calculator questions
Does Kelly predict my chance of winning?
No. You enter the probability. The calculation optimizes a mathematical growth model under that assumption; an inaccurate estimate can produce a misleading allocation. Positive EV does not guarantee a winning settlement.
What are half Kelly and quarter Kelly?
They multiply the full Kelly bankroll fraction by 0.5 or 0.25. They are not 50% or 25% of your entire bankroll. The tool starts at quarter Kelly as an example, without treating any fraction as personally suitable.
How are fees and contract quantities handled?
Binary mode adds the entered cents-per-contract fee to the price and assumes it is paid in either outcome. The model rounds quantity down to whole contracts. It does not apply any platform fee schedule, fixed order fee, outcome-dependent fee or rebate. Standard odds mode excludes fees.
Can I apply the result to several correlated positions?
This tool models one long position in isolation. It does not optimize a portfolio, account for existing exposures or evaluate correlation. Copying a separate full Kelly allocation into multiple positions can exceed the bankroll or concentrate risk.
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