In this guide
The primary obstacle preventing skilled forecasters from succeeding in prediction markets is seldom inaccurate forecasting — rather, it is inadequate capital allocation. An astute probability assessment becomes worthless if a prolonged losing run depletes your entire stake. This guide outlines the methodology that safeguards against such outcomes.
The Kelly Criterion: The Mathematical Foundation
The Kelly Criterion determines the theoretically ideal proportion of your capital to allocate to each wager: f = (bp - q) / b
- b = net odds received (e.g., if YES costs 0.40, b = 1.5)
- p = your probability estimate
- q = 1 - p
- Result: optimal fraction of bankroll for this position
In practice: use half-Kelly. Although Kelly delivers mathematical optimality under conditions of certainty, our probability assessments contain inherent estimation error, making half-Kelly the superior choice for improved risk-adjusted returns.
Hard Rules: Never Break These
- Maximum 5% of bankroll per single position — no exceptions regardless of conviction
- Maximum 25% of bankroll in any single correlated cluster — e.g., all US election markets
- Stop-loss: if you lose 25% of your starting bankroll in a month, stop trading for the rest of the month
- Never add to a losing position to "average down" — reevaluate the fundamental thesis first
Drawdown Recovery
Temporary losses occur regularly, even among traders possessing genuine edge. Following a 20% decline in account value, cut your stake sizes in half until your account recovers to its previous peak. This approach mitigates the risk that unfavourable market conditions escalate into account destruction.
FAQ
- How much starting capital do I need for serious prediction market trading?
- £500–1,000 supplies sufficient funds to build adequate exposure across 10–20 separate trades using half-Kelly allocation. Below £100, sizing constraints prevent you from implementing rigorous, systematic methodologies effectively.
- What should I do after a winning streak?
- Increase caution rather than confidence. Consecutive wins breed complacency and poor judgement. Maintain your disciplined allocation framework irrespective of short-term results.