Kelly Strategy: A Guide to Bankroll Management in Betting

What is the Kelly Strategy?

The Kelly Strategy, also known as the Kelly Criterion, is a mathematical formula used to determine the optimal size of a bet. Its goal is not to maximize profit on a single wager, but to optimize the growth of one's capital (bankroll) over the long term while managing the risk of ruin.

A bit of history

The criterion was developed by John L. Kelly Jr., a scientist working at AT&T's Bell Labs in the 1950s. Initially, his research was not related to betting but to information theory and noise problems in long-distance telephone signals. However, the betting and investment community quickly recognized the potential of his formula for capital management.

How does the Kelly Strategy work?

The Kelly Strategy formula calculates the percentage of your bankroll to wager on a "value bet," which is a bet where the odds are believed to be higher than the true probability of the event occurring. The basic formula is:

f = (bp - q) / b

Where:

• f: Is the fraction of the bankroll to bet.
• b: Is the decimal odds of the bet minus 1 (e.g., odds 2.50, b = 1.50).
• p: Is the probability of winning that you have estimated (e.g., 0.45 for 45%).
• q: Is the probability of losing (1 - p).

If the result of the formula (f) is negative or zero, it means there is no value in the bet, and according to the criterion, you should not bet anything.

A practical example

Let's imagine you have a bankroll of €100.

• Odds for Team A to win: 3.00
• Our estimated probability of winning: 40% (or 0.40)

Let's calculate the variables:

• b = 3.00 - 1 = 2.00
• p = 0.40
• q = 1 - 0.40 = 0.60

Let's apply the formula:

f = (2.00 * 0.40 - 0.60) / 2.00 = (0.80 - 0.60) / 2.00 = 0.20 / 2.00 = 0.10

The result is 0.10, which corresponds to 10%. We should therefore bet 10% of our bankroll, which is €10 (10% of €100).

Pros and Cons of the Kelly Strategy

Pros

• Optimal bankroll growth: If the probability estimates are correct, the strategy maximizes the growth rate of capital in the long run.
• Risk protection: The method inherently reduces the risk of wiping out the bankroll, as the stake is always a fraction of the available capital.

Cons

• Probability estimation: Its success depends entirely on the bettor's ability to estimate true probabilities more accurately than the bookmaker.
• Volatility: The "full" Kelly can be very aggressive and lead to high stakes, resulting in significant bankroll fluctuations. For this reason, many bettors use fractional Kelly (e.g., Half Kelly or Quarter Kelly).

How to apply the Kelly Strategy with Betting Manager Pro

Manually managing Kelly Strategy calculations for every bet can be complex and time-consuming. The good news is that you can automate the entire process. By using an app like Betting Manager Pro, available for iOS and Android, you can set the Kelly Strategy as your bankroll management system. The app will perform the calculations for you, allowing you to focus solely on analyzing and selecting your bets, while tracking performance accurately and automatically.