Kelly Criterion
The Kelly Criterion is a mathematical formula that calculates the optimal position size as a percentage of your account to maximise long-term growth. It uses win rate and risk-reward ratio as inputs.
Formula
Example: Win rate 50%, average win $200, average loss $100 (W/L ratio = 2): Kelly = 0.5 − (0.5 ÷ 2) = 0.5 − 0.25 = 25% of account per trade.
Why it matters for traders
Kelly Criterion provides a mathematical basis for position sizing. Full Kelly is often considered too aggressive for trading; most traders use Half-Kelly (half the calculated percentage) to smooth out the variance.
How Tradapt tracks this
Use Tradapt's Kelly Criterion Calculator to find your optimal position size based on your actual win rate and risk-reward ratio from your trade history.
Track this free in TradaptFrequently asked questions
Should I use the Kelly Criterion for position sizing?
The Kelly Criterion gives you a theoretical maximum. In practice, most traders use 25–50% of full Kelly (called 'fractional Kelly') to reduce variance while maintaining positive growth. Full Kelly produces volatile equity curves even with a positive edge.