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Kelly Criterion Calculator — Optimal Position Size

The Kelly formula tells you what percentage of capital to risk per trade for maximum long-term growth. Includes Half-Kelly and Quarter-Kelly variants.

e.g. 2 = winners are twice the size of losers.

Full Kelly position size
32.50%

Theoretically optimal % of capital to risk. In practice, most traders use a fraction of this for safety.

Half Kelly (recommended)
16.25%

Most pros use this — same expected growth, ~75% less volatility.

Quarter Kelly (conservative)
8.13%

For early-career traders still calibrating their edge.

Reality check: the Kelly Criterion assumes your win rate and W/L ratio are known constants. They aren't. Most traders overestimate their edge — that's why half-Kelly is the standard.
About this tool

What Kelly tells you

The Kelly Criterion answers a deceptively hard question: given a known edge, what % of bankroll should I bet to maximise long-term growth? The answer is f = p − q/b, where p is win rate, q is loss rate, and b is the win/loss ratio.

Why most traders use Half-Kelly

Full Kelly is theoretically optimal but assumes your edge is known with certainty. In real trading, you're estimating edge from a small sample — over-estimation by 2× means you blow up. Half-Kelly captures most of the long-term growth while cutting drawdown volatility roughly in half.

Negative Kelly

If Kelly returns a negative number, it's telling you the trade has negative expected value. Stop taking it. No amount of position sizing turns a losing edge into a winning one.

How to use the Kelly Criterion Calculator

Takes about a minute. No signup, no download, your data stays in your browser.

  1. 1
    Open the tool. Scroll up to the Kelly Criterion Calculator above — it loads instantly in your browser, no install needed.
  2. 2
    Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
  3. 3
    Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.

Frequently asked questions

Common questions about the Kelly Criterion Calculator.

Is the Kelly Criterion Calculator free to use?

Yes. The Kelly Criterion Calculatoron 7BusyBoss is completely free — no signup, no paywall, no usage cap.

Do I need to sign up to use the Kelly Criterion Calculator?

No. The Kelly Criterion Calculatorworks instantly in your browser — no account needed. Signing in with Google is optional and only unlocks features like saving favorites and higher AI build limits.

Does the Kelly Criterion Calculator work on mobile?

Yes. Every tool on 7BusyBoss is mobile-responsive and works in any modern browser — Chrome, Safari, Firefox, Edge — on phones, tablets and desktops.

Is my data safe when I use the Kelly Criterion Calculator?

Yes. The Kelly Criterion Calculatorruns entirely in your browser — your inputs never leave your device unless the tool explicitly fetches public data (e.g. currency rates). We don't store the values you type.

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