Kelly Criterion Calculator

Author: Henrick Yau
- 7 October 2026
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Calculators

Calculate optimal bet sizes using the Kelly Criterion formula. This calculator helps determine the percentage of your bankroll to wager to maximise long-term growth while managing risk.

Betting Parameters

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Bet Information

%

Advanced Options

(1 = full Kelly)

About Kelly Criterion

The Kelly Criterion is a mathematical formula that helps determine the optimal size of a series of bets to maximise the logarithm of wealth over the long term. It was developed by J. L. Kelly, Jr. while working at Bell Labs in 1956.

Benefits of Kelly Criterion
  • Bankroll Growth: Maximises the long-term growth rate of your bankroll.
  • Risk Management: Automatically adjusts bet sizes based on your edge.
  • Consistency: Provides a systematic approach to betting rather than arbitrary bet sizing.
Limitations and Considerations
  • Volatility: Full Kelly betting can lead to significant bankroll swings.
  • Estimation Error: The formula assumes you know the true probability of winning, which is rarely the case.
  • Fractional Kelly: Many professional bettors use fractional Kelly (such as Half-Kelly or Quarter-Kelly) to reduce variance.
  • Applicability: Kelly works best for bets with a positive expected value; it will recommend not betting when there's no edge.
How to Use This Calculator
  1. Enter your current bankroll amount.
  2. Select your preferred odds format and enter the betting odds offered.
  3. Input your estimated true probability of winning the bet.
  4. Choose a Kelly fraction (less than 1 for a more conservative approach).
  5. Click "Calculate" to see the recommended bet size and supporting information.

What Is the Kelly Criterion Calculator?

The Kelly Criterion Calculator is a tool designed to help you determine how much of your bankroll you should bet on a given wager. By using this calculator, you can find the optimal bet size to maximise your chances of long-term success while keeping your risk in check. Itโ€™s based on a mathematical formula that has been used in gambling and investing for many years.

Understanding the Basics of Betting

Before using the calculator, itโ€™s important to grasp a few basic concepts. You need to know your current bankroll, the odds of the bet, and your perceived chances of winning. Understanding these elements allows the calculator to provide you with a more accurate recommendation on how much to stake on each bet.

Key features for bankroll management and simulation

  • Bankroll Management: Helps you manage your funds wisely by calculating the percentage to bet.
  • Odds Formats: Offers different ways to input odds, including American, decimal, and fractional formats.
  • Simulation Options: Visualise how your bankroll would grow over time using different betting strategies.

Entering your bankroll, odds and win probability

Using the Kelly Criterion Calculator is straightforward. You start by entering your current bankroll amount. Then, you select your preferred odds format and input the betting odds. Finally, you'll add your estimated true probability of winning. These simple inputs allow the calculator to do all the heavy lifting for you.

Benefits of Using the Kelly Criterion

  • Optimises Growth: It focuses on maximising the long-term growth of your bankroll.
  • Risk-Adjusted Betting: Adjusts your bet size based on your perceived edge over the odds offered.
  • Systematic Approach: Eliminates guesswork, leading to more consistent betting practices.

Limitations: bankroll swings and probability accuracy

While the Kelly Criterion has many advantages, it also has some downsides. One major limitation is the potential for significant swings in your bankroll, especially if you opt for full Kelly betting. Additionally, the formula relies on having an accurate assessment of your winning probability, which can be difficult to determine. Many bettors choose to use a fraction of the recommended bet size to mitigate these risks.

The Calculation Steps Explained

The calculator uses the formula: Kelly % = (bp - q) / b. Here, b represents the decimal odds minus one, p is the probability of winning, and q is the probability of losing. Understanding this formula can deepen your appreciation of how the calculator arrives at its recommendations.

Strategic betting with the Kelly Criterion Calculator

The Kelly Criterion Calculator is an invaluable tool for anyone serious about betting. It takes the guesswork out of how much to bet, making your approach more strategic. Whether you're a seasoned bettor or just getting started, this calculator can help you make informed decisions while managing risk effectively.

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