Kelly criterion calculator

The growth-optimal stake, and why to bet less.

Interactive: Kelly criterionEasy

The growth-optimal fraction of capital — and why nearly everyone bets less than it.

Win probability % Win / loss ratio

Expected edge: —
Full Kelly stake: —
Half Kelly stake: —
Reading: —

Full Kelly is a wild ride — drawdowns of 50% are routine even when the edge is real, and the formula assumes you know p and b exactly (you don't). Practitioners run a half or a quarter of it, accepting slower growth for a survivable path. Set the win probability below the break-even and the answer becomes the only correct one: don't bet.

The idea behind it

This calculator belongs to Diversification & Correlation, where the mechanism it computes is explained step by step, with the formula, what each input means and where the simple model stops being right. Everything is computed in your browser; nothing you type is sent anywhere.

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Not advice. This explains how something works; it is not a recommendation, and nothing here is tailored to you. You can lose everything you put in — with leveraged instruments, considerably more. StrikeAndYield is not a regulated firm and provides no financial services.

The same in full — six points, and why each one matters

No advice, no recommendation. Nothing on this page constitutes investment, financial, legal, tax or accounting advice, a personal recommendation, or an offer or solicitation to buy or sell any financial instrument.
Nothing here is tailored to you. This is written for a general audience. It does not consider your objectives, financial situation, knowledge, time horizon or tolerance for loss.
The examples are simplified. Worked examples use round numbers and leave out costs, spreads, taxes, collateral, settlement and market conventions that materially change real outcomes.
The models are teaching models. Formulas shown are standard textbook formulations. Institutions add calibration, live market data and credit, funding and capital adjustments — nothing here will reproduce a dealer’s quote or produce a valuation you can rely on.
These instruments carry risk. You can lose your entire investment. Leveraged instruments — futures, options, CFDs, perpetual futures and similar — can cost you considerably more than you originally deposited.
We are not a regulated firm. StrikeAndYield is an independent publication by DELISORIA. It is not a bank, broker, fund manager or licensed adviser, it provides no financial services, and reading it creates no client relationship. For decisions about your own money, consult a professional licensed in your jurisdiction. See the full disclaimer.