Calculate the mathematically optimal stake size that maximises long-term bankroll growth while minimising risk of ruin. Used by professional bettors and investors worldwide.
Enter the probability you believe the selection will win. Be honest — overestimating your edge is the #1 mistake with Kelly staking.
Input the decimal odds being offered and your total bankroll. The calculator needs all three values to determine the optimal stake.
Use the half-Kelly recommendation for a safer approach. The Kelly curve chart shows how your expected growth rate changes with different stake sizes.
The Kelly Criterion, developed by John L. Kelly Jr. at Bell Labs in 1956, is the gold standard for optimal position sizing. It calculates the stake that maximises the expected logarithmic growth of your bankroll over time.
The formula is elegantly simple: f* = (bp − q) / b, where b = decimal odds − 1, p = probability of winning, and q = probability of losing (1 − p). The result is the fraction of your bankroll you should wager.
In practice, most professional bettors use Half Kelly or Quarter Kelly. Full Kelly staking is mathematically optimal but produces extreme variance. Half Kelly captures roughly 75% of the growth rate with significantly less volatility — a much smoother ride for your bankroll.
The Kelly Criterion only works when you have a genuine positive expected value. If your estimated probability doesn’t exceed the implied probability of the odds, Kelly says don’t bet. This is perhaps its most valuable lesson: discipline to pass on bad bets.
See Also: See how Kelly staking performs over hundreds of bets with our Staking Strategy Comparison simulator. To understand your risk of ruin under different staking levels, try the Ruin Probability Calculator.
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