Kelly criterion

A staking formula that prescribes the optimal stake size as a percentage of bankroll, given a known edge. Kelly stake = (bp − q) / b, where b is the decimal odds minus 1, p is the true win probability, and q is 1 − p. Maximises long-run bankroll growth in theory; in practice most punters use fractional Kelly (e.g. half-Kelly) because true probabilities are estimated, not known.