In this guide
The primary cause of skilled forecasters struggling in prediction markets isn't inaccurate forecasts — it's inadequate capital preservation. Even a sound probability assessment becomes worthless if a prolonged losing run depletes your entire stake. This guide outlines the protective strategy you need.
The Kelly Criterion: The Mathematical Foundation
The Kelly Criterion determines the mathematically ideal percentage of your capital to allocate to each individual trade: 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. Whilst Kelly maximises returns under perfect probability knowledge, our real-world estimates carry inherent uncertainty, making half-Kelly a superior choice for managing risk-adjusted performance.
Hard Rules: Never Break These
- Maximum 5% of bankroll per single position — without exception, irrespective of how confident you feel
- Maximum 25% of bankroll in any single correlated cluster — for instance, all United States election-related 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" — reassess your core investment thesis before committing additional funds
Drawdown Recovery
Temporary performance declines occur regularly, even amongst traders with genuine edge. Following a 20% drawdown, scale back your position sizes by half until you regain your previous peak. This approach shields you from a rough patch spiralling into total account destruction.
FAQ
- How much starting capital do I need for serious prediction market trading?
- £350–700 (approximately $500–1,000) gives sufficient funds to build adequate exposure across 10–20 positions using half-Kelly allocation. Below £70 (approximately $100), position constraints become prohibitively restrictive and undermine systematic application.
- What should I do after a winning streak?
- Increase caution rather than confidence. Successful runs breed complacency and poor judgement. Maintain your disciplined sizing framework regardless of short-term results.