I noticed that in the crypto community, more and more people are discussing mathematical approaches to position management. And here’s what’s interesting—the Kelly criterion, a formula from 1956, still remains one of the most effective strategies for determining bet size. Why is this important at all? Because most traders either risk too much or too little. The golden mean—that’s what everyone is looking for.

The history of this approach is quite intriguing. John L. Kelly Jr. developed his formula at Bell Laboratories, originally to optimize signals for long-distance communication. But then the mathematician Edward O. Thorp applied this idea to blackjack, and it changed the entire gambling industry. Later, the Kelly criterion made its way into finance; it became especially popular in the 1980s, when investors realized how well it works for portfolio management.

The formula itself is simple: f* = (bp - q)/b. Where f is the fraction of capital for the bet, p is the probability of winning, q is the probability of losing, and b is the profit coefficient. In practice, this means that you put into the trade only that part of your capital that corresponds to your real edge in the market. No emotions—just mathematics.

In crypto trading, applying the Kelly criterion requires several steps. First, you need to honestly estimate the probability that your trade will be profitable—that’s the hardest part, because crypto markets are unpredictable. Then you determine your maximum risk per trade. After that, you use the formula to calculate the optimal position size. Then you constantly reassess all the parameters as market conditions change.

Let me take a concrete example. Suppose you think the probability of a coin rising is 60%, and the potential payoff is twice the stake (coefficient 2:1). According to the Kelly criterion, f* = 0.4, meaning it’s optimal to invest 40% of your capital in this trade. Sounds aggressive? Yes, it can be risky—especially in volatile crypto markets.

This is where the real difficulties of applying the Kelly criterion in crypto come in. First, volatility. Asset prices can jump by 20–30% within hours, and your probability calculations can become irrelevant. Second, external factors—news, regulation, technological events—they strongly affect the market, but the formula doesn’t take them into account. Third, the psychological factor. If the Kelly criterion recommends investing 40% of your capital, and you see the position going into the red, that can be psychologically difficult.

There’s also another point—commissions, slippage, taxes. All of these eat into profit, but the basic Kelly formula doesn’t account for them. Therefore, in practice traders often use not the full size calculated by the formula, but half or even a quarter—so-called fractional Kelly.

The Kelly criterion is not a magic wand. It’s a tool that helps you make more disciplined decisions and avoid two extremes: total ruin due to excessive risk, or missed opportunities due to trading too cautiously. But you need to apply it wisely, taking into account the real conditions of crypto markets and your own risk tolerance. Without constant analysis and adjustments, this strategy can lead to serious losses. So use the Kelly criterion as part of a comprehensive risk-management approach, not as the only benchmark for trading.