Why Use This Kelly Criterion Calculator
The Kelly Criterion is a mathematically proven formula for optimal position sizing. This Kelly bet calculator helps you:
- 💰 Calculate Optimal Bet Size — find the mathematically optimal fraction.
- 📊 Understand Your Edge — see how your win rate and ratio affect sizing.
- ⚖️ Reduce Risk — use fractional Kelly for conservative sizing.
- 📈 Visualize Growth — see the expected growth rate.
- 📜 Track Your History — save, review, and export past calculations.
- 🔒 100% Private — all calculations run locally.
Kelly Criterion Formula Used by This Tool
Kelly Fraction = (bp - q) / b
Where: - b = Win/Loss Ratio (Average Win ÷ Average Loss) - p = Win Probability (as a decimal) - q = Loss Probability = 1 - p
Optimal Bet Size = Kelly Fraction × Account Balance × Fractional Kelly
Expected Growth Rate = p × ln(1 + b × f) + q × ln(1 - f)
Where f is the Kelly fraction.
How to Use This Kelly Criterion Calculator
- Select your account currency from the picker in the site header.
- Enter your win probability (your historical win rate).
- Enter your win/loss ratio (average win ÷ average loss).
- Enter your account balance.
- Set your fractional Kelly (100% for full Kelly, 50% for half-Kelly).
- View your results instantly — see your optimal bet size, amount to risk, and expected growth rate.
Frequently Asked Questions
What is the Kelly Criterion?
The Kelly Criterion is a formula used to determine the optimal size of a series of bets. It maximizes the expected log growth of your capital over the long run.
What is the Kelly formula?
f* = (bp - q) / b, where f* is the fraction of capital to bet, b is the net odds (win/loss ratio), p is the win probability, and q is the loss probability (1 - p).
What is fractional Kelly?
Fractional Kelly is a conservative version where you risk only a fraction (e.g., 50% or 25%) of the full Kelly bet. This reduces volatility while preserving much of the growth.
What is a good Kelly percentage?
A good Kelly percentage depends on your risk tolerance. Full Kelly can be aggressive. Many traders use half-Kelly (50%) to reduce drawdowns while maintaining good growth.
Can I use this for trading?
Yes — the Kelly Criterion is widely used by traders to size positions based on their edge and win rate.