Kelly Calculator

Bankroll fraction · Growth · Estimation error

Chicago · --:--

Kelly assumes you know your win rate and payoff exactly. You do not — you estimated them from a finite number of trades, and Kelly is unusually sensitive to that error. Overestimating your edge by a few points can turn the “optimal” bet into one that loses money over time, because the penalty for overbetting is far steeper than for underbetting. This is why practitioners use a half or quarter of the figure rather than the full one.

📈 Kelly Calculator

Compute optimal bankroll fraction with Kelly Criterion. Get quick bets for 1×, ½×, ¼× Kelly and expected growth.

↔️ Position Sizer ← Dashboard

⚙️ Inputs

💼 Bankroll ($)

Your trading capital used for sizing.

✅ Win Rate (%)

Probability your trade wins.

🏆 Payoff Ratio (b)

Average win / average loss. Example: 1.8 means wins are 1.8× losses.

🧮 Advanced

Cap Kelly at (%)

Risk controls: hard cap even if Kelly suggests more.

Fractions to show

Comma-separated multipliers of Kelly (e.g., 1 = full Kelly).

Fees + Slippage per bet ($)

We adjust effective edge slightly.

Formula: f* = (b·p − q) / b, where p = win rate, q = 1−p, b = payoff ratio.

📋 Results

--Kelly Fraction

--Bet Size ($)

--Expected log‑growth

--Breakeven Win %

Plan	Fraction of Kelly	Risk (% bankroll)	Bet Size ($)	Exp. log‑growth (per bet)

Enter inputs and hit Calculate. Tip: Many pros use ½‑Kelly to reduce drawdowns.