Once you have a profitable edge, the next question is: how much should you risk per trade to grow capital fastest over the long run? The Kelly Criterion answers that — but it gives a theoretical ceiling, not a target. Bet a fraction of it, protect against drawdowns, and journal everything, and you build a compounding machine.
Kelly Criterion: K = W − (1 − W) ÷ R (W = win rate, R = reward-to-risk ratio)
K is the fraction of capital that maximizes long-term geometric growth
If K ≤ 0 → do NOT take the trade. Your edge is negative.
Full Kelly is the theoretical ceiling, not a target — disciplined traders bet a fraction of it
Lesson
Kelly Criterion — and Why You Bet a Fraction of It
Kelly tells you the bet size that grows capital fastest over many trades. But it assumes you know your true win rate and payoff exactly — and you don't, you estimate them. Overbetting a Kelly built on optimistic estimates leads to brutal drawdowns, so professionals trade a fraction of Kelly.
The formula: K = W − (1 − W) ÷ R (W = win rate, R = reward-to-risk)
Example: W = 55%, R = 3 → K = 0.55 − 0.45 ÷ 3 = 0.55 − 0.15 = 0.40 (40%)
Even-money shortcut: when R = 1, the formula simplifies to K = 2W − 1 (e.g., 60% win rate → 20%)
Full Kelly is too aggressive in practice: it assumes perfectly known odds and produces violent swings
Fractional Kelly: betting half- or quarter-Kelly keeps most of the growth with far smaller drawdowns — this is what pros actually use
Drawdown asymmetry: losing 50% requires a 100% gain to recover — protect capital first
Compounding is the real edge: consistent, survivable returns compound exponentially over time
The Pareto reality: a small share of trades produces most of your profit — so cut losers fast and let winners run (this shapes your exits, not your bet size)
Journal EVERY trade: entry, stop, target, risk%, actual R, screenshot — accurate stats are what make Kelly usable at all
Check Yourself
Your strategy wins 60% of the time on 1:1 risk/reward trades. Kelly works out to ≈20%. How should you actually size your trades?
Risk the full 20% on every trade — it is the mathematically optimal bet
Bet only a fraction of Kelly (half- or quarter-Kelly) to limit drawdowns from estimate error
Risk 60% — your win rate is your position size
Kelly is negative here, so you should skip the trade entirely
Answer it (with a live chart) in the interactive lesson.
Liquidity Theory · Learn · Analyze · Trade together Educational content only — trading involves substantial risk and most beginners lose money. Nothing here is financial advice.