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I discuss the dangers that may come from naively trusting the Kelly criterion’s suggestions and propose a practical solution. This practical solution is fully in line with how I invest at Junto. In the first section, I introduce the mental model of gambler’s ruin and the mental model of leverage.

## Proportional Staking

We have verified how betting with Kelly formula is doing when the outcome probabilities are not exactly the ones we believe in. We’ve applied the Kelly formula to the simple betting game. Let’s do the same analysis as above for when the coin has odds 65/35, and we bet either 20% or 30% of our capital. We can clearly see that having 20% of capital “invested” in each bet is riskier – with each bet we put more money at stake, but do we receive more reward for that? Blue lines are significantly more dispersed than the red ones, some of the blue runs finish with capital larger than the red ones, but also a prominent group ends with much smaller winnings. We could calculate easily Kelly ratios for each of above scenarios if we knew the real probabilities.

## How Kelly Criterion Works Exactly

For obvious reason, you don’t want to bet in any game where the expected payout is 0 or negative. How do serious sports bettors approach their wagering? What are the key differences between casual punters and professional bettors? If you’ source re serious about sharpening your betting intelligence, the bettingexpert Academy guide to Advanced Betting Theory provides you with the tools and techniques to truly take your sports betting to the next level. To take your reasoning seriously, the reason why you might not want to bet 1 cent at a time is because the Kelly bet is guaranteed to eventually overtake your 1-cent-bet-strategy. Furthermore, it is completely incorrect to say that the Kelly bet has a 1/4 chance of losing all your money in the given situation.

A positive percentage implies an edge in favour of your bankroll, so your funds grow exponentially. You can also test the criterion for different values in this online sheet by using the code below. We also showed that, in the long term, such strategies increase the probability of ruin. Note that we do not imply that the player should invariably use , but rather just in the general scenario studied here. Given further information, using may actually be advantageous.

While these are technically “up” rounds, that company is going sideways. And, of course, if you think the probability of success is only 10% but exit is imminent it’s probably your thought process you should worry about, not your portfolio allocation. The good news is that this issue can be easily overcome if you just reduce the amount of the stake suggested by the formula a little. Many bettors go with the so-called fractional Kelly strategy, according to which they need to use a fraction of the stake suggested by the formula. The two examples express a negative value and show that it is not worth placing a bet on either opportunity because it has a negative expected value. On the surface of it, the second situation seems to offer a good chance of success, but once you do the calculations, you realise that it is not a wise idea to risk your money, as the odds are not high enough.

## Optimizing Investment Sizing With The Kelly Criterion

The latter is also valued more than the tangent portfolio but, consistent with the literature, it presents more pronounced drawdowns. This strategy is compared with the Half Kelly, the Triple Kelly and the buy-and-hold strategies considering Banca Intesa as a unique asset. For sake of simplicity, we assume there are no transaction costs, and that the risk-free rate corresponds to the borrowing rate. In the previous sections we have described the Kelly criterion and its properties. All the computations presented in the following are performed using the R software for statistical computing installed on a PC equipped with a Intel i9 5.3 GHz processor. Beside investing in a single financial asset it is also possible to compose portfolios optimized under the Kelly criterion.

By applying the Kelly criterion method properly, using completely accurate inputs, you are certain to see your bankroll grow exponentially. Inject those numbers into the Kelly Criterion formula with the available odds, and the result will be as accurate as reasonably possible. Now, we look at the straight bet on this game, and we see the lines set at Team A 1.65, and Team B 2.70. Sports predictions are base on probability and need consistent wagering as per the advice of the winning betting system to succeed. If there was a universal winning formula at our disposal, the bookies would not be working and would most likely change something about their approach.

In the following we use the term Kelly portfolio to refer to such a kind of portfolio. Growth rate function G for different proportions of wealth . For instance, let’s assume that Arsenal have a 50% probability of winning.