
The Kelly Criterion is a mathematical formula that can help you make informed betting decisions. It's a powerful tool that can maximize your expected value, but it's not as complicated as you might think.
The Kelly Criterion is based on the idea of proportional betting, where you bet a portion of your bankroll based on the probability of winning. This approach is different from fixed-odds betting, where you bet a fixed amount on every bet.
To use the Kelly Criterion, you need to calculate the edge of your bet, which is the difference between the true probability of winning and the odds offered by the bookmaker. For example, if the true probability of winning is 60% and the odds offered are 1.67, the edge of the bet is 0.06 or 6%.
The Kelly Criterion formula is: b = (bp - q) / b, where b is the fraction of the bankroll to bet, p is the true probability of winning, and q is the true probability of losing.
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Understanding the Formula
The Kelly Criterion formula is a mathematical equation that helps you determine the optimal amount to bet based on the probability of winning and the odds of the bet. It's a relatively simple concept, but it requires some basic math to understand.
To calculate the Kelly Criterion, you need to know three things: the probability of winning (p), the probability of losing (q), and the proportion of the bet gained with a win (b). For example, if you're betting on a coin toss and the true odds of heads are 60%, then p = 0.6 and q = 0.4.
Here's a breakdown of the formula:
- b = the proportion of the bet gained with a win
- p = the probability of winning
- q = the probability of losing (q = 1 - p)
- f∗ = (bp - q) / b
The result of the formula is the fraction of the bankroll to wager, which is represented by f∗. For instance, if the true odds of heads are 60% and the proportion of the bet gained with a win is 1 (even money), then f∗ = (0.6 - 0.4) / 1 = 0.2, or 20%. This means you should bet 20% of your bankroll on the coin showing heads to maximize your upside and minimize your downside.
The Equation

The Kelly Criterion is a mathematical formula that helps bettors calculate the optimal amount to bet. It's a simple equation, but it's not always easy to understand.
The Kelly Criterion formula is: f∗ = p × (b - 1) / b, where p is the probability of winning, b is the odds, and f∗ is the fraction of the bankroll to bet.
For example, if you're betting on a coin toss with true odds of 0.60 and given odds of 1, the Kelly Criterion would recommend betting 20% of your bankroll. This is because K% = (1 × 0.60 – 0.40) / 1 = 0.20 or 20%.
Here's a breakdown of the variables:
- b = 1 (your odds, the same as +100 in sports betting)
- p = 0.60 (the probability of winning)
- q = 1 – 0.60 = 0.40 (the probability of losing)
In this case, the Kelly Criterion recommends betting 20% of your bankroll.

In general, the Kelly Criterion suggests that you should bet a fraction of your bankroll that is proportional to the probability of winning and the odds. If the odds are in your favor, you should bet a larger fraction of your bankroll. If the odds are against you, you should bet a smaller fraction of your bankroll.
Here's a table to help illustrate the concept:
Note that the Kelly Criterion is not a guarantee of success, but rather a way to maximize your rate of capital growth over the long term.
Multiple Outcomes
In the world of formulas, multiple outcomes are a reality. The formula can produce different results depending on the inputs and variables involved.
A good example of this is the formula for calculating the area of a circle, which is A = πr^2. This formula can produce a wide range of areas, from a tiny fraction of a square inch to a massive square mile.

The formula for calculating the volume of a rectangular prism, V = lwh, is another example. This formula can produce different volumes depending on the length, width, and height of the prism.
The more variables you have in a formula, the more possible outcomes you can get. For instance, the formula for calculating the area of a triangle, A = (b × h) / 2, has two variables: base and height.
This can be a bit overwhelming, but it's also an opportunity to explore and learn. By experimenting with different inputs and variables, you can see how the formula responds and what kind of outcomes you can get.
What's the Standard?
The Kelly Criterion is a mathematical formula that helps you determine the optimal amount to bet on a given situation. It's designed to maximize your long-run growth rate and minimize the risk of losing everything.
The formula is based on several key factors, including the probability of winning (p), the probability of losing (q), and the proportion of the bet gained with a win (b). If the probability of winning is 60% (p=0.6), the probability of losing is 40% (q=0.4), and the proportion of the bet gained with a win is 1:1 (b=1), the formula recommends betting 20% of your bankroll (f∗ = 0.6 - 0.4/1 = 0.2).

The Kelly Criterion is often used in situations where you have an advantage, such as in investing or sports betting. In these cases, the formula helps you determine the optimal bet size to maximize your returns while minimizing your risk.
To illustrate this, let's consider an example. If you have a 60% chance of winning and you receive 1:1 odds on a winning bet, the formula recommends betting 20% of your bankroll. This means that if you have $100 in your bankroll, you should bet $20 on each opportunity.
Here's a summary of the Kelly Criterion formula:
Note that if the probability of winning is 50%, the formula recommends betting nothing (0%). If the probability of winning is less than 50%, the formula recommends betting a negative amount, indicating that you should take the other side of the bet.
The Kelly Criterion is a powerful tool for managing risk and maximizing returns in situations where you have an advantage. By understanding how to apply this formula, you can make more informed decisions and achieve your financial goals.
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Applying the Kelly Criterion
The Kelly Criterion formula is used to calculate the optimal bet size that maximizes upside and minimizes downside.
To apply the Kelly Criterion, you need to know the true odds and the given odds. For example, if the true odds of a coin flip are 60% and the given odds are 1 (or +100), the Kelly Criterion formula would suggest staking 20% of your bankroll on the coin showing heads.
The formula is: K% = (1 × 0.60 – 0.40) / 1 = 0.20 or 20%.
If the calculation spits out zero or a negative number, it means the criterion suggests betting nothing and walking away because the odds aren’t in your favor.
What is Kelly Staking in Sports Betting?
Kelly Staking is a bankroll management strategy developed by computer scientist John Kelly in 1956. It's a formula that helps you determine the optimal amount to bet based on the odds and your bankroll.
The Kelly Criterion is widely recognized as the "truest" sports betting bankroll management strategy. It's been used by sports bettors and Wall Street traders to protect assets and maximize earnings.
To use the Kelly Criterion, you need to calculate the fraction of your bankroll to bet. This is done by plugging in the odds and your estimated probability of winning into the formula. For example, if you think the Seahawks have a 55% implied probability of winning, and the odds are 1.9, the calculation would be: (0.9 × 0.55 – 0.45) ÷ 0.9 = 0.05.
A positive percentage implies favourable odds, which means you should bet a portion of your bankroll. However, if the calculation spits out zero or a negative number, it means the odds aren't in your favour, and you should bet nothing.
Here's a breakdown of the Kelly Criterion formula:
A negative outcome could mean it's better to lay the Seahawks on a betting exchange or back the Broncos if you believe they're overpriced.
How to Apply for Sports Betting?
Applying the Kelly Criterion to sports betting is a straightforward process. To start, you'll need to determine the posted and true odds of the bet.
The posted odds of a bet can be found on the sportsbook's website or at the betting window. For example, in the Cowboys vs. Eagles scenario, the Cowboys moneyline was set at -110, which translates to a 52.5% implied probability.
To calculate the true odds of a bet, you need to have a strong opinion on the outcome. In the same scenario, the true odds of the Cowboys moneyline were estimated at 55%.
Now that you have the posted and true odds, you can apply the Kelly Criterion formula to determine the optimal bet size. The formula is: K% = (true odds ÷ posted odds) - (1 - true odds).
Using this formula, we can calculate the Kelly Criterion percentage for the Cowboys moneyline: K% = (0.55 ÷ 0.91) - (1 - 0.55) = 0.055. This means that you should bet 5.5% of your total bankroll on the Cowboys moneyline.
Here's a simple table to illustrate the Kelly Criterion calculation:
Note that a negative Kelly Criterion percentage indicates a bet that should be avoided.
Betting Experiment – Behavioural Example
In a study, participants were given $25 to place even-money bets on a coin that would land heads 60% of the time.
28% of the participants went bust, and the average payout was just $91.
Only 21% of the participants reached the maximum prize of $250.
A remarkable 18 of the 61 participants bet everything on one toss, while two-thirds gambled on tails at some stage in the experiment.
The Kelly criterion suggests betting 20% of one's bankroll on each toss of the coin, which would result in a 2.034% average gain each round.
The theoretical expected wealth after 300 rounds, without the cap, would be $10,505.
A strategy of betting only 12% of the pot on each toss would have even better results, with a 95% probability of reaching the cap and an average payout of $242.03.
Return Rates and Probabilities
The Kelly criterion takes into account all possible events when dealing with continuous return rates on an investment or bet. This means it's essential to consider every possible outcome.
Continuous return rates can be complex, but the Kelly criterion provides a framework for making informed decisions. By accounting for all possible events, you can make more accurate predictions and optimize your growth rate coefficient.
The Kelly criterion is designed to help you maximize your growth rate, but it's not a guarantee of success. It's a tool that requires careful consideration of probabilities and return rates.
Binary Return Rates
Binary return rates are a type of investment or betting system where the return is either a win or a loss of a fixed percentage of the bet.
In such systems, the Kelly criterion comes into play, which is a mathematical formula for determining the optimal betting percentage. The Kelly criterion for binary return rates yields a very specific solution for this optimal percentage.
This means that if you're considering investing or betting in a binary return rate system, you should look into the Kelly criterion to determine the best betting strategy.
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Non-Binary Return Rates
Non-binary return rates can be complex, but it's essential to consider all possible events when dealing with continuous return rates.
The Kelly criterion, for instance, takes into account all possible events, making it a useful tool for optimizing growth rates.
Continuous return rates can be found in various investments and bets, and understanding them is crucial for making informed decisions.
In the context of the Kelly criterion, the optimal growth rate coefficient must consider all possible events, which can be a challenge to calculate.
This is where the Kelly criterion shines, providing a mathematical framework for optimizing growth rates in the face of uncertainty.
Theoretical Background
The Kelly criterion betting strategy is based on a mathematical formula that calculates the optimal amount to bet in order to maximize long-term growth. This formula was developed by John L. Kelly Jr. in 1956.
The Kelly criterion is a way to balance the potential gain of a bet with the potential loss, taking into account the probability of winning and the probability of losing.
The Kelly formula is: b = (bp - q) / b, where b is the fraction of the bankroll to bet, p is the probability of winning, and q is the probability of losing.
The Kelly criterion assumes that the bettor has a large enough bankroll to withstand the potential losses.
A bankroll of $10,000 is generally considered sufficient to apply the Kelly criterion, but this can vary depending on the individual's betting strategy.
Criticisms and Limitations
Some economists have argued against the Kelly strategy, pointing out that an individual's specific investing constraints may override the desire for optimal growth rate.
The Kelly criterion requires accurate probability values, which isn't always possible for real-world event outcomes. This can lead to overestimation of true probabilities, causing the criterion value to diverge from the optimal and increasing the risk of ruin.
Kelly supporters often recommend fractional Kelly betting, which involves betting a fixed fraction of the amount recommended by Kelly, to reduce volatility and protect against non-deterministic errors in advantage calculations.
The Kelly criterion is often misunderstood as being equivalent to asset diversification, but it's actually a form of "time diversification", taking equal risk during different sequential time periods.
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Play to Your Strengths

The Kelly system is designed to help you avoid ruin by betting only where you have an advantage.
In the market, this means finding favorable odds where you can exploit them.
You might have an advantage due to your unique combination of skills that few others have.
Kelly's system is based on the idea that you must keep quiet about your advantage to avoid it becoming public knowledge.
This means that you should stop betting when your private information becomes public knowledge.
The system is not just about betting on rigged horse races, but also about finding opportunities in the market where you have an advantage.
Building a skill stack in areas you already have an advantage is a key part of the Kelly system.
This approach can help you make the most of your strengths and avoid betting on unfavorable odds.
Bernoulli
Daniel Bernoulli made a significant contribution to the field of decision-making with his 1738 article, which suggested that one should choose investments with the highest geometric mean of outcomes.
This idea is mathematically equivalent to the Kelly criterion, although Bernoulli's motivation was different, as he wanted to resolve the St. Petersburg paradox.
Bernoulli's work was well known among mathematicians and economists, even though an English translation of his article wasn't published until 1954.
Criticism

The Kelly strategy has its fair share of critics, who argue that its promise of optimal growth rate may not always be achievable in real-world investing.
Some economists argue that individual investing constraints can override the desire for optimal growth rate, making the Kelly strategy less effective.
In fact, the conventional alternative to the Kelly strategy is expected utility theory, which suggests that bets should be sized to maximize the expected utility of the outcome.
This is especially true for individuals with logarithmic utility, as the Kelly bet maximizes expected utility for them, making the Kelly strategy a suitable choice.
However, even Kelly supporters often recommend fractional Kelly betting, which involves betting a fixed fraction of the amount recommended by Kelly, to reduce volatility and protect against errors in advantage calculations.
The Kelly criterion requires accurate probability values, which can be challenging to obtain in real-world event outcomes, making it prone to errors.
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Here are some key criticisms of the Kelly strategy:
- Requires accurate probability values, which may not always be possible
- Can lead to increased risk of ruin if probability values are overestimated
- Does not account for individual investing constraints
- May not be suitable for all types of investments or gambles
These criticisms highlight the importance of carefully considering the limitations of the Kelly strategy before applying it to real-world investing or gambling.
Frequently Asked Questions
What is the difference between Kelly Criterion and flat betting?
The Kelly Criterion adjusts your stake based on perceived value to maximize long-term growth, whereas flat betting involves betting the same amount regardless of the situation. This key difference makes Kelly Criterion a more dynamic and risk-managed approach to betting.
What is the Kelly method formula?
The Kelly method formula is k% = (bp - q) / b, where b is the odds of winning, p is the probability of winning, and q is the probability of losing. This formula helps determine the optimal bet size to maximize long-term wealth.
What is the Kelly multiplier in sports betting?
The Kelly Multiplier is a formula that helps determine the optimal amount to wager based on the probability of winning and losing a bet, allowing you to maximize your expected value. By adjusting the multiplier, you can adjust the risk level of your bets.
What is the optimal F Kelly formula?
The optimal Kelly formula is f = μ / σ^2, where μ is the expected return and σ is the standard deviation of the investment. This formula calculates the ideal leverage to maximize returns while minimizing risk.
What is an example of a Kelly Criterion bet?
The Kelly Criterion recommends a 4% bet on a coin with a 52% chance of landing on heads, assuming a fair odds of 2.00. This example illustrates how the Kelly Criterion adjusts bets based on the true probability of an event.
Sources
- https://en.wikipedia.org/wiki/Kelly_criterion
- https://www.wealest.com/articles/kelly-criterion
- https://insights.matchbook.com/betting-strategy/the-kelly-criterion/
- https://oddsjam.com/betting-education/what-is-the-kelly-criterion-in-sports-betting
- https://help.outlier.bet/en/articles/8269411-understanding-how-to-use-kelly-criterion
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