Kelly criterion calculator
Explore a theoretical Kelly allocation using your own probability estimate, odds and chosen fraction.
Your calculation
A worked example
At +100 with an assumed 55% win probability, full Kelly is 10% of bankroll. Using a quarter of that fraction gives 2.5%, or $25 for a $1,000 bankroll. The result changes if the probability estimate is wrong.
The math
With decimal odds d and win probability p: full Kelly = max(0, (p × d − 1) ÷ (d − 1)). Selected fraction = full Kelly × your multiplier. Dollar allocation = bankroll × selected fraction.
The underlying growth-rate framework comes from J. L. Kelly Jr.’s 1956 paper, A New Interpretation of Information Rate. This tool implements the simplified single-bet formula above.
Common questions
Why does the allocation become zero?
If the estimated probability does not exceed the price’s break-even threshold, the formula has no positive allocation. Negative values are floored at zero rather than presented as a short position.
Is quarter Kelly safe?
No fixed fraction makes an unreliable probability estimate safe. Reducing the multiplier changes the amount, but losses, correlated outcomes and estimation error remain.
Why does a 100% probability produce such a large result?
The model treats your input as certainty. That assumption can produce a full-bankroll allocation at full Kelly. It is a mathematical consequence of the input, not evidence that the outcome is certain or that risking the bankroll is appropriate.
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