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Calculate optimal bet sizing for maximum growth.
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Kelly Criterion Calculator computes the stake fraction that mathematically maximises long-term capital growth, given your win probability and payoff ratio, a foundational concept in betting and position sizing.
The formula, f = (bp − q) ÷ b, returns the fraction of capital to stake for optimal compounded growth. But its power comes with a sharp caveat: full Kelly is aggressive and assumes you know your true edge exactly. Since edges are usually estimated, overconfidence leads full Kelly to oversize and court severe drawdowns, which is why seasoned practitioners use fractional Kelly (half or quarter), trading a little theoretical growth for much greater safety.
A profound insight it encodes is that more is not better: betting above the Kelly fraction increases risk while actually reducing long-term growth and raising the probability of ruin. Kelly marks the growth-optimal ceiling, making it a rigorous argument against the over-sizing that blows up accounts.
Crucially, Kelly only helps if you truly have an edge and estimate it accurately, it sizes bets, it doesn't create an advantage, and applied to losing propositions it just sizes losses. It's educational, not financial or betting advice, and runs in your browser. Pair it with the Position Size and Risk-Reward calculators.
| Price | Free, no signup, no paywall, no watermark |
|---|---|
| Works on | Any modern browser: desktop, tablet, and mobile |
| Processing | In your browser, files never leave your device |
| Account required | None |
| Category | Business Tools |
Enter your estimated win probability and the win/loss payoff ratio
The tool computes the Kelly fraction (% of capital to stake)
Consider a fractional Kelly (e.g. half) for safety
Use it as a sizing guide, not a guarantee
Calculates the Kelly Criterion optimal stake fraction
From win probability and win/loss ratio
Used in betting and position sizing
Includes guidance on fractional Kelly
Runs in your browser, your figures stay on your device
Free, with no signup and no limit on calculations
Estimating an optimal bet or position size from your edge
Understanding risk-optimal sizing mathematically
Applying fractional Kelly for safer sizing
Learning the Kelly Criterion
Use fractional Kelly (half or quarter), full Kelly is aggressive and punishes overestimated edges
Never bet above Kelly, it raises risk while reducing growth and courting ruin
Kelly only helps if you genuinely have an edge and estimate it accurately; it can't create one
Common questions about this tool, its workflow, and what to expect before you use it.
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Calculate optimal bet sizing for maximum growth.
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