What Is the Kelly Criterion?
The Kelly Criterion is a betting strategy that helps you decide how much of your bankroll to stake on a given bet. Instead of betting blindly or using flat stakes, the Kelly formula uses probability and odds to calculate the optimal stake size that maximizes long-term growth while minimizing the risk of going broke.
In simple terms:
- If you bet too much, you risk losing your bankroll quickly.
- If you bet too little, you miss out on profits.
- Kelly finds the balance.
The Kelly Criterion Formula Explained
The basic formula looks like this:
Where:
- f* = fraction of your bankroll to bet
- b = decimal odds – 1 (for example, odds 2.50 → b = 1.5)
- p = probability of winning (your own estimation, not the bookmaker’s)
- q = probability of losing (1 – p)
👉 Example:
- Your estimate: a team has a 60% chance of winning.
- Bookmaker odds: 2.20 (implied probability = 45%).
- Then:
That means you should bet 20% of your bankroll if you’re following Full Kelly.
Full Kelly vs. Half Kelly
- Full Kelly = bet exactly what the formula says.
- Half Kelly = bet half of that amount.
Why use Half Kelly? Because it smooths out volatility. Even if your probabilities are a bit off, you won’t lose your bankroll too quickly.
👉 Many professional bettors recommend Half Kelly in practice. That’s why search terms like half kelly criterion calculator are so popular.
Kelly Criterion Stake Calculator
Manually calculating can be annoying, especially if you want to test many bets. That’s why bettors often search for a kelly criterion stake calculator. With a calculator, you just enter:
- Bookmaker odds
- Your estimated probability
- Bankroll amount
The calculator instantly gives you the optimal stake (Full Kelly) and the safer option (Half Kelly).
💡 In BetRocket, you can go one step further:
- Use our EV+ Lab to backtest Kelly Criterion strategies on historical data.
- Find EV+ bets in real time, where Kelly works best.
- Automatically see whether Full Kelly or Half Kelly makes sense for your bankroll.
This way you’re not just using theory — you’re applying it directly to real betting opportunities.
Why Bettors Use the Kelly Criterion
- Bankroll management: never risk more than you should.
- Compounding growth: Kelly maximizes long-term profit.
- Mathematical edge: It only works if you find value bets (where your estimated probability is higher than the implied odds).
Limitations of the Kelly Criterion
- Requires accurate probability estimates — if you’re wrong, Kelly can suggest over-betting.
- Full Kelly is aggressive and can lead to high variance.
- Works best with a large sample size of bets.
That’s why many bettors combine Half Kelly with tools like BetRocket that identify positive EV bets.
Conclusion
The Kelly Criterion is one of the smartest bankroll management tools in sports betting. Whether you use a kelly criterion stake calculator or go with half kelly criterion calculator for safety, the method helps you bet smarter, not harder.
And if you want to take it further, try BetRocket — our platform finds EV+ bets and lets you backtest Kelly strategies with the EV+ Lab.
👉 Start today and see how mathematical betting strategies can improve your results.