Estimate disciplined unit sizing and Kelly-based exposure from your bankroll, odds, and probability estimate.
Method
The calculator shows a fixed unit size and a Kelly-based stake. Kelly sizing uses odds and estimated probability to find a theoretical growth-maximizing fraction; half-Kelly reduces that exposure to account for estimation error and volatility.
Educational example
With a $1,000 bankroll, decimal odds of 2.00, and a 55% estimated probability, full Kelly is 10%.
Half Kelly is 5%, or $50. A small probability error can materially change this result, so conservative caps remain important.
Express decisions as a stable percentage of bankroll.
Use fractional Kelly to reduce sensitivity to probability error.
Compare one proposed stake with total portfolio exposure.
Kelly assumes a reliable probability estimate, known payout, repeatable opportunities, and a long time horizon. Drawdowns can still be severe, and a bankroll should never include money needed for essential expenses.
A unit is a fixed fraction of a dedicated bankroll used to compare stake sizes consistently.
It reduces volatility and the damage caused by overconfident probability estimates.
Yes. When the entered assumptions do not show an edge, the Kelly fraction is zero or negative.