calculator
Kelly Calculator
Use fractional Kelly to estimate sizing based on your edge. (Recommended: 25% Kelly or less.)
Kelly sizing
Enter American odds and your true win probability. Optional: bankroll for $ sizing.
Bet % of bankroll: —
Bet size ($): —
Why fractional Kelly
Full Kelly is aggressive. Fractional keeps you alive through variance.
Kelly maximizes long-run growth *if your probability estimate is correct*. In the real world, probabilities are noisy. That’s why fractional Kelly is the move — it reduces risk of ruin and keeps sizing stable.
- 25% Kelly is common for serious bettors
- If your “edge” is a guess, size smaller
- Use no-vig + EV tools to sharpen inputs
Mini FAQ
Why did I get 0%? Your inputs don’t show an edge (or probability too low).
Is Kelly “required”? No — but it’s a solid reference point.