# Kelly Criterion System

Kelly Criterion SystemKelly's Criterion is a system for managing the sports betting bank. It uses a special formula to determine the optimal bet size you place on the selection you choose.

The equation is as follows:

D = decimal coefficient minus 1

S = probability of success (between 0 and 1)

F = probability of failure (which will be 1 minus "probability of success")

Bet = ((d x s) - f) / d

This most likely looks like a rather complicated formula, but you will find that it is not complicated when you use it several times. Here's an example of Kelly's criterion in action:

You have a bank (this is the money in the bookmaker's account) of 500 leva. You have found a football game with a home winning ratio of 2.00 and you think that the probability of success of this bet will be 55%. The first thing you need to do is complete the three variables. "D" in this example will be 1.00 (decimal factor 2.00 minus 1), "s" will be 0.55 (equal to 55% probability of success) and "f" will be 0.45 (Equal to 45% chance of failure).

Now fill out the formula:

Bet = ((1.00 x 0.55) - 0.45) / 1.00

Bet = (0.55 - 0.45) / 1

Bet = 0.1 / 1

Bet = 0.10

The final result is the share of your total bank you have to bet on this match. If your bank has 500 leva, the bet must be 50 leva (0.1 x 500 leva).

System hazards

The first and most dangerous underwater stone of Kelly's criterion is the need to be very precise in determining the real probability of success of the bet - inventing an arbitrary number will not do the job. And this may be the most difficult task in the betting world. In the above example, if the player has made a mistake and has incorrectly determined that the probability of winning the hosts is 65% (instead of the real chance of 55%), Kelly's criterion would have advised him to put a bet of $ 150. To use this system, you need to be very confident in your calculations.

The second danger is that sometimes the recommended bet can be too much of your bank, even if you have correctly determined your probability of winning. The above example results in a 10% stake in the entire bank, which is a rather aggressive approach compared to other bank management strategies. In this respect, the risk can be reduced. Many players use half-Kelly or a quarter-Kelly strategy. That is, they bet only half or a quarter of the amount shown at the end of the calculation. This will make the system much less risky.

Although not a danger, the problem is also the fact that the strategy is intended for no more than one bet at the same time, because after each new bet you will have a new size of the bank. What do we do, for example, in the afternoon of Saturday when there are several interesting matches from the English and European championships? You may find eight matches with a good chance of success, and once you make each individual calculation, the system will show you that you have to bet a total of 112% of your bank, which is clearly not possible!

However, if you have "perfect" information about the probability of success, Kelly's criterion is the best option as it leads to optimal winnings. Unfortunately, this "perfect" information is difficult to achieve.

If you decide to use the system, we recommend that you initially bet a quarter or a half Kelly to limit the risk until you know it.