The Kelly Criterion answers the most important question in betting: how much should I stake? Too little and you leave money on the table. Too much and a losing streak wipes you out. Kelly gives the mathematically optimal answer.
The Formula
Kelly % = Edge / (Odds - 1)
Edge = (True Probability x Odds) - 1
If you have a 10% edge at odds of 2.00, Kelly says stake 10% of your bankroll. At odds of 3.00, Kelly says 5%.
Why Full Kelly is Dangerous
Full Kelly maximises long-term growth rate but produces extreme volatility. A bad run can drawdown 50-70% of your bankroll. In practice, professionals use fractional Kelly:
- Half Kelly (recommended): 75% of the growth rate, significantly less variance
- Quarter Kelly (conservative): 50% of the growth rate, very smooth equity curve
The Cap
Regardless of calculated Kelly, never stake more than 5% of your bankroll on a single bet. This protects against estimation errors — if your edge calculation is slightly wrong, a capped stake prevents catastrophic loss.
At Athenea Apex
Every pick includes Full, Half, and Quarter Kelly recommendations. We recommend Half Kelly as the default — it balances growth and risk for sustainable bankroll building.