Kelly Criterion Calculator

About this calculator

The Kelly criterion computes the bankroll fraction that maximizes long-run geometric growth: f* = p − q/b, where p is your win probability, q = 1−p, and b is the net decimal odds (payout multiple minus 1). It's derived by maximizing the expected logarithm of wealth rather than expected value directly, which is what makes it avoid the ruin risk of always betting the full edge you perceive.

Professional sports bettors and poker players use fractional Kelly (often 25–50% of the full Kelly stake) to size bets aggressively enough to compound an edge quickly while limiting the swings a full-Kelly bankroll would suffer from probability estimation errors. The same formula, reframed with expected return and variance, underlies position-sizing models used by quantitative traders and portfolio managers deciding how much capital to allocate to a single wager or investment with a known edge.