Kelly Criterion Calculator
The bet size that maximizes long-run growth for a given edge. Full Kelly is a wild ride; professionals run half or quarter Kelly for the same edge with far less pain.
Results (live)
Estimates only, not financial advice. All math runs in your browser; nothing you type leaves this page.
How it works
Kelly % = (p × (b + 1) − 1) ÷ b, where p = win probability, b = win/loss ratio
Worked example
55% wins at 1.5:1 gives full Kelly of 25%: violent swings. Half Kelly at 12.5% keeps most of the growth with roughly half the drawdown.
FAQ
Why not bet full Kelly?
It assumes your probabilities are exact. Overestimate your edge slightly and full Kelly over-bets into ruin territory; fractional Kelly forgives estimation error.
What if Kelly comes out negative?
Your parameters describe a losing strategy. No sizing fixes a negative edge; the tool will tell you plainly.
Related calculators
Estimates only, not financial, tax or investment advice. Verify numbers against your exchange or a professional before acting.