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Kelly Criterion Calculator
The Kelly criterion tells you the bet size that grows your account fastest for a given edge. Set your win rate and reward to risk to see your Kelly fraction, and why most traders use only a fraction of it.
The Kelly criterion is a formula for the bet size that grows your capital fastest over the long run, given your edge. Bet more than Kelly and your growth actually slows while your risk explodes; bet less and you grow slower but far safer.
How it works
Enter your win rate and your reward to risk, then Calculate. The blue curve shows how your long-run growth changes with bet size, peaking exactly at the Kelly fraction. Half Kelly is the safer setting most traders actually run.
Your edge
Growth is not linear in bet size
Notice the curve: growth rises to a single peak at the Kelly fraction, then falls off a cliff. Just past the peak you take much more risk for less growth, and beyond a point growth turns negative even with a real edge. That is why oversizing is so dangerous, and why disciplined position sizing beats chasing bigger bets.
Frequently asked
What is a good Kelly percentage?
Kelly outputs can be surprisingly high. Full Kelly is very aggressive and assumes your edge is exact, so most traders use half Kelly or less to survive estimation error and deep drawdowns.
Why not just bet full Kelly?
Full Kelly maximises growth in theory but produces brutal drawdowns and punishes any overestimate of your edge. Fractional Kelly keeps most of the growth with far less risk.
Size positions with the same discipline across a whole strategy. Build and backtest it on years of data, no code.
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