Kelly Criterion Calculator
Calculate optimal bet sizing using the Kelly Criterion formula. Maximize long-term bankroll growth while managing risk.
Kelly Criterion Calculator
Calculate optimal bet sizing using the Kelly Criterion formula
Implied Probability: 40.0%
💡 You have an edge when your estimated win probability exceeds the implied probability from the odds.
Formula
f* = (bp - q) / bWhere f* is the fraction of bankroll to bet, b is the net odds, p is win probability, and q is loss probability (1-p).
How to Use
- 1Enter odds — Input the odds offered by the bookmaker in American or Decimal format.
- 2Estimate probability — Enter your estimated probability of winning (this requires skill and research).
- 3Enter bankroll — Input your total betting bankroll.
- 4View recommendation — See the optimal bet size and consider using fractional Kelly for safety.
Frequently Asked Questions
What is the Kelly Criterion?
The Kelly Criterion is a mathematical formula that determines the optimal size of a series of bets to maximize long-term growth of your bankroll. It was developed by John Kelly at Bell Labs in 1956.
Why use Half Kelly or Quarter Kelly?
Full Kelly can be very aggressive and lead to large swings in your bankroll. Half Kelly provides about 75% of the growth rate with significantly less variance. Quarter Kelly is even more conservative. Most professional bettors use fractional Kelly.
What does "edge" mean in betting?
Edge is the advantage you have over the bookmaker. If you estimate a 55% chance of winning but the odds imply only 50%, you have a 5% edge. Kelly only recommends betting when you have a positive edge.
How do I estimate win probability?
Estimating true probabilities requires research, statistical analysis, and experience. You might use historical data, power ratings, situational factors, and other information to form your estimate.
What if Kelly suggests not betting?
If Kelly returns 0%, it means you don't have an edge at the given odds. Either your probability estimate is too low, or the odds aren't favorable enough. Don't bet without an edge.