Fractional Kelly Adjuster

Overview

This pillar implements the Fractional Kelly Criterion, a proven risk management strategy for bet sizing. It calculates an optimal, yet conservative, stake to protect your bankroll from volatility and inaccurate probability estimates.

What It Does

The pillar takes your estimated probability of an event and the market odds to calculate the full Kelly Criterion bet size. It then applies a conservative multiplier, or 'fraction', to this value. This reduces the recommended stake, accounting for real-world model uncertainty and preventing the aggressive swings associated with the full Kelly formula.

Why It Matters

The standard Kelly Criterion is theoretically optimal but practically dangerous, as it assumes perfect knowledge of probabilities. By using a fraction, this pillar provides a crucial margin of safety, preventing catastrophic losses and ensuring you can survive downturns to realize your long-term edge.

How It Works

First, you input the market's decimal odds and your own estimated probability of winning. The pillar calculates the 'edge' and the full Kelly stake percentage. Finally, it multiplies this percentage by a user-defined fraction (e.g., 0.5 for half-Kelly) to provide a final, risk-adjusted bet size.

Methodology

The calculation uses the formula: Adjusted Bet % = Fraction * ((Decimal Odds * Win Probability - 1) / (Decimal Odds - 1)). The 'Fraction' is a constant between 0.1 and 1.0, representing the user's risk tolerance and confidence in their probability estimate. Win Probability is derived from other pillars or user analysis.

Edge & Advantage

It prevents bankroll wipeouts caused by the over-aggressiveness of the full Kelly Criterion, keeping you in the game long enough for your analytical edge to materialize.

Key Indicators

• Adjusted Bet Size

  high

  The final, recommended percentage of bankroll to wager after applying the Kelly fraction.

• Kelly Fraction

  high

  The conservative multiplier (e.g., 0.1 to 0.5) applied to the full Kelly value to reduce risk.

• Implied Edge

  medium

  The perceived advantage in the bet, which is the core input for the Kelly calculation.

Data Sources

• User Input / Pillar Outputs

  Requires the user's estimated probability of an outcome and the current market odds.

Example Questions This Pillar Answers

• → How much of my bankroll should I risk on a 'Yes' contract at 60c if I believe the true probability is 70%?
• → Given the high uncertainty in my model for the election, what is a safe but effective bet size?
• → What is the optimal, risk-adjusted stake for a crypto price target market with 2.5x odds?

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