Free Kelly criterion calculator. Enter the odds, your win probability and bankroll to find the optimal stake, with full, half and quarter Kelly options.
The Kelly criterion is a staking formula that tells you what fraction of your bankroll to bet to maximise long-term growth, given the odds and your estimated probability of winning. Bet too much and you risk ruin; bet too little and your bankroll grows slowly. Kelly finds the mathematically optimal middle.
If the result is zero or negative, the bet has no edge and Kelly says stake nothing. The calculator also shows your edge (expected value): odds × probability − 1.
Odds of 2.50 with a 50% win chance: b = 1.5, p = 0.5, q = 0.5, so f* = (1.5 × 0.5 − 0.5) / 1.5 = 16.7% of your bankroll. On a $1,000 bankroll that is $167 at full Kelly, or $83 at half Kelly.
Full Kelly is aggressive and assumes your probability estimate is exactly right. Because real estimates are uncertain, many bettors use half or quarter Kelly to cut variance and drawdowns while keeping most of the growth. The key input is honest probability — garbage in, garbage out.