Kelly Capital Sizing Tool
Type your total capital, the decimal multiplier, and your honest estimate of the probability. Betbizi works out your edge and the mathematically optimal allocation, plus the half and quarter Kelly fractions the professionals actually use.
Be honest with this number. First find your edge with the Value and Vig Checker, then size the allocation here.
Awaiting Inputs
Type your capital, the multiplier, and your probability to size the position.
Kelly only works if your probability estimate is honest. Overestimate your edge and Kelly will happily over-allocate. 18+. Play responsibly. SARGF Helpline: 0800 006 008.
How the math works
1. The edge
Your edge is what your estimated probability earns over what the multiplier implies. A multiplier of 2.00 implies a 50% chance. If your research says 55%, you hold roughly a 10% edge per rand allocated.
2. The Kelly fraction
Kelly divides your edge by the multiplier minus one. The result is the fraction of your capital that grows it fastest over hundreds of positions, without risking ruin.
3. Why fractional Kelly
Full Kelly assumes your numbers are perfect, and they never are. Half or quarter Kelly captures most of the growth with a fraction of the swings. That is the professional move.
On R1,000 capital with a 10% edge at a 2.00 multiplier, full Kelly says allocate R100. That feels small, and that is the point. Anyone telling you to risk 30% of your capital on a sure thing is selling you a story, not math. The analysts who survive are the ones who allocate small and stay in the game.
Questions, answered
What is the Kelly Criterion?
A formula that sizes a position from your edge: edge divided by the multiplier minus one. It tells you the fraction of your capital to allocate for optimal long-term growth without ruin.
Why half or quarter Kelly?
Because your probability estimate is never exact. Fractional Kelly keeps most of the growth and cuts the swings, so a few wrong reads cannot wreck your capital.
What if Kelly says no position?
Then your probability estimate does not beat the multiplier and your edge is negative. The correct allocation is zero. Walking away is a winning decision, not a missed one.
Is this tool free and private?
Yes. Free forever, no sign-up, and it runs entirely in your browser. Nothing you type is ever sent to our servers.