Kelly Criterion Calculator

Estimate what fraction of capital the classic Kelly formula implies from your win rate and average win versus average loss, then compare half- and quarter-Kelly.

Kelly uses your edge (win probability and payoff ratio) to suggest position sizing in a simplified model. It assumes stable probabilities and does not know your risk tolerance or real-world constraints.

Formula used: fraction equals win probability minus (1 minus win probability) divided by (average win divided by average loss). Negative values mean the edge is negative at those inputs.

Payoff (avg win ÷ avg loss)2
Full Kelly32.50%
Half Kelly16.25%
Quarter Kelly8.13%

Frequently Asked Questions

It is a formula that suggests a fraction of capital to risk when you know your win probability and the ratio of average win to average loss. Full Kelly maximizes long-run growth in theory but can be very aggressive and volatile.
Many traders use a fraction of full Kelly because real estimates of win rate and payoff are uncertain, and full Kelly can imply large drawdowns. Half or quarter Kelly is a common way to be more conservative.
No. The output is educational. Real markets have fat tails, changing edges, and correlation. Do not bet your full account based on this calculator alone.
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