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What is the Kelly Criterion for investing?

What is the Kelly Criterion for investing?

Understanding the Kelly Criterion aids in risk management and decision-making, crucial for effective financial management.

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The Kelly criterion is a mathematical method of choosing optimal bets.

The formula, which was invented by John Kelly in 1956, helps you determine the amount of money you should bet at any given time. It’s often used in sports betting, but it can be applied to anything from roulette and other games of chance to investing and asset allocation.

If that sounds like something that would interest you, and maybe help you develop new strategies regarding your investments, then keep reading!

The Kelly criterion was first picked up by gamblers who wanted to improve their odds of betting on horse races
The Kelly criterion was first picked up by gamblers who wanted to improve their odds of betting on horse races. | Photo: Pexels

What is the Kelly criterion?

The Kelly criterion is a formula for choosing optimal bets. It’s used to determine the amount of money you should bet at any given time, in order to maximize your returns.

The Kelly criterion has drawn some of the most well-known investors on the planet, including Warren Buffett, Charlie Munger, Mohnish Pabrai, and Bill Gross, despite its relative obscurity and lack of mainstream academic support.

The formula is more complicated than it may seem at first glance, but once you understand the basics you’ll be able to use it as an investing tool.

Currently, gamblers and investors utilize the Kelly criterion to manage risk and money, figuring out what proportion of their bankroll or capital should be used in each wager or transaction to maximize long-term gain.

The Kelly criterion is a formula that can be used to determine the optimal size of a bet. It’s applicable to any game with an element of chance, such as sports betting and roulette.

The Kelly criterion, which was first published in 1956, was soon adopted by gamblers who were able to use the formula for horse racing. The formula wasn’t applied to investing until much later.

Because of the news that the renowned investors Warren Buffett and Bill Gross employ a variation of the Kelly criterion for their wealth, the technique has had a surge in popularity much more lately.

The formula considers that the investor would reinvest earnings and put them at risk for subsequent trades and is employed by investors who desire to trade with the goal of increasing capital. The formula’s objective is to establish the ideal investment amount for each trade.

The Kelly criterion formula has two essential elements:

  • Winning probability factor (W): The likelihood that a deal will result in a profit.
  • Win/loss ratio (R): This is calculated by dividing the total amount of positive trades by the total amount of negative trades.

Investors can use the formula’s output to determine what portion of their overall capital should go into each investment.

The Kelly percentage, or K%, is the equation’s result and has a number of practical uses. The Kelly criterion can be used by gamblers to optimize the size of their wagers. It can be used by investors to calculate the percentage of their portfolio that should be allocated to each investment.

How does the Kelly criterion apply to investing?

Investors very quickly learn the value of diversification and how much cash to allocate to each stock or industry.

All of these inquiries can be used to evaluate a method for managing finances, such as the Kelly Criterion, one of the various allocation strategies available for doing so. The Kelly strategy, Kelly formula, or Kelly bet are further names for this approach.

The Kelly Criterion is a framework for determining how much you should be investing at any given time. It’s also helpful in deciding when to invest and when not to invest, based on your risk tolerance and goals.

How can you use the Kelly criterion to hedge your bets in the stock market?

The Kelly criterion is used to determine the optimal amount of money to invest in the stock market. It’s a mathematical formula that can be used to help you determine the amount of money you should bet at any given time, and it can also be used as a hedge for your bets.

Follow these easy steps to leverage Kelly’s approach as an investor:

Access the past 50–60 trades you made. You can check if you claimed all of your trades by simply calling your broker or looking at your most recent tax filings.

If you are an experienced trader with a well-developed trading strategy, you may just backtest the strategy and use the findings. However, the Kelly Criterion makes the assumption that you trade in the same manner as you did in the past.

Determine “W,” the likelihood of winning. To achieve this, divide the total number of trades you made by the number of trades that had a profit (both positive and negative). The closer it is to one, the better this number is. Any value over 0.50 is desirable.

Determine the win/loss ratio, or “R.” Divide the average gain of the winning transactions by the average loss of the losing trades to achieve this.

If your average gains are higher than your average losses, you should have a number greater than one. As long as the number of losing trades stays low, a result of less than one is doable.

Enter these figures into Kelly’s equation found here. Note the Kelly proportion that the equation yields.

The magnitude of the positions you ought to be taking is represented by the percentage (a value less than one) that the equation yields.

Take a 5% position in each of the stocks in your portfolio, for instance, if the Kelly percentage is 0.05. In essence, this approach tells you how much diversification is appropriate.

However, the system does call for some common sense. One thing to remember is to allocate no more than 20% to 25% of your capital to one equity, regardless of what the Kelly percentage may suggest. Any further allocation entails investing risk that most people shouldn’t be incurring.

What are the limitations of the Kelly criterion?

There are some people that doubt the Kelly Criteria formula. Several economists have argued against the approach despite the fact that it promises to outperform all others in the long term.

Their main concern is that an individual’s unique investing limits may come before the goal for the best growth rate.

In actuality, the decision-making capacity of an investor is significantly influenced by their limits, whether or not they are self-imposed. The anticipated utility theory, which states that bets should be sized to maximize expected utility of outcomes, is the traditional option.

Despite its popularity, the Kelly criterion is not suitable for all types of betting and investing. It does not work well with assets that are highly volatile or have low odds of success.

It also doesn’t work well with short-term investments if you want to make a lot of money quickly; in this case, it is better to use binomial trees or other methods.

The Kelly criterion is also only applicable when your investment has an expected return greater than zero (e.g., if you’re investing in something like stocks). If this isn’t true–say someone puts their entire savings into bitcoin without understanding how volatile it could be–then using this method could very easily lead them into bankruptcy.

Does the Kelly criterion Work?

Pure mathematics is the foundation of this system. Some individuals might doubt the applicability of this logic, which was initially devised for telephones, in the stock market or the gambling industry.

An equity chart can prove the system’s performance by simulating the growth of a specific account using only mathematical formulas.

In other words, the investor must be expected to be able to maintain such performance and the two variables must be entered accurately or else the efficacy of the method diminishes.

What you should remember is that there isn’t a perfect money management system. This approach will effectively assist you in diversifying your investment portfolio, but it is limited in many ways.

It cannot help you choose successful stocks or anticipate sudden market crashes (although it can lighten the blow). In the markets, there is always a certain level of “luck” or chance that might change your returns.

Although effective diversification cannot guarantee that you will always earn great results, it can help you minimize losses and increase gains. The Kelly Criterion then is one of the many various models you may use to aid in diversification.

The Kelly criterion helps with diversification and asset allocation
The Kelly criterion helps with diversification and asset allocation. | Photo: Pexels

What can I learn from the Kelly criterion with regards to asset allocation?

Asset allocation is the process of dividing your investments among different asset classes. It can be thought of as a kind of portfolio balancing act, where each asset class contributes something unique to your portfolio.

Asset allocation has been shown to be one of the most important factors in determining investment success.

One should not commit more than 20% to 25% of the capital into single equity regardless of what the Kelly criterion says, since diversification itself is important and essential to avoid a large loss in the event a stock fails.

Some investors prefer to bet less than the Kelly percentage due to being risk-averse, which is understandable, as it means that it reduces the impact of possible over-estimation and depleting the bankroll. It is known as Fractional Kelly.

On the other hand, if the Kelly percentage results in a percentage less than 0%, it means that the Kelly criterion is recommending that one walk away and not bet anything at all since the odds do not seem to be in one’s favor based on the formula and mathematical calculation.

Following the Kelly criterion typically results in success due to the formula is based on a simple formula using pure mathematics.

However, factors that can impact the success include accurate inputs of the probabilities of winning and losing, as an incorrect percentage would be detrimental.

In addition to that, there may be unexpected events such as stock market crashes, which would impact all stocks regardless if the Kelly criterion was used or not.

The Kelly Criterion can help you determine how much of each asset class you should hold in order to maximize returns while minimizing risk.

Regardless, investors should diversify their portfolios because it reduces risk and increases returns.

Diversification is spreading your assets over different assets or asset classes. Asset classes are broad categories of investments such as stocks, bonds or cash equivalents.

For example, if you have money in a savings account, it’s considered part of the cash equivalent class because it doesn’t earn much interest and isn’t likely to appreciate in value over time (although some savings accounts will give you an interest rate that increases with time).

If you have $5 million invested in stocks, then those stocks are considered part of the stock class because they could increase or decrease significantly in value over time based on factors such as company performance or market conditions.

The goal of diversification is to reduce risk by having a mix of different asset classes so if one falls dramatically in value (or loses liquidity), it won’t affect your overall portfolio too.

Diversification is a key tool that investors can use to reduce the riskiness of their portfolio and protect themselves from major market swings. Diversification means that you hold many different types of investments in your portfolio, rather than just one or two.

Diversification is important for two reasons:

It reduces volatility. When there are a variety of investments in your portfolio, some will likely perform well when others do poorly. This helps smooth out the ups and downs of your overall returns over time.

It protects against unforeseen events. If one investment performs poorly, it could drag down other parts of your portfolio if they’re highly correlated — but if they’re not highly correlated, they’ll have less of an impact on each other’s performance.


The Kelly Criterion is a mathematical method of choosing optimal bets. It can help you decide how much to invest at any given time and also determine your optimal asset allocation.

However, it is important to keep in mind that no method will perfectly give you an easy shortcut to your financial goals. There is no magic recipe for that, and it is also why it is beneficial to have the aid of financial experts to guide you to where you want your finances to go.

Pained by financial indecision? Want to invest with Adam?

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Adam is an internationally recognised author on financial matters, with over 760.2 million answer views on Quora.com, a widely sold book on Amazon, and a contributor on Forbes.

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