Separate the model from the stake decision
Kelly is a mathematical growth rule under specific assumptions, including an accurate probability estimate and a repeatable opportunity. It is not evidence that a probability is accurate. At +120 and 50%, full Kelly is 8.33% of bankroll. Multiplying by one quarter gives 2.083%, or $20.83 for a $1,000 bankroll before the optional cap.
Understand the fraction and the cap
The selected fraction scales the full-Kelly result. A cap then limits the stake further; it does not increase a smaller calculated stake. For example, a 1% cap on a $1,000 bankroll limits the preceding $20.83 figure to $10. Zero or negative estimated advantage returns a zero stake. These outputs describe the inputs, not a recommended personal budget.
Why probability error matters
If the true win probability is lower than the input, a stake can be too large even when the calculator is working correctly. Fractional Kelly reduces exposure relative to full Kelly but cannot turn a negative expectation into a positive one. Try a lower plausible probability and compare the result before interpreting the original figure.
One position is not a portfolio
The calculator evaluates a single bet in isolation. Several bets involving the same team, player or game may lose together, and separately calculated stakes do not account for that correlation. Bankroll also means money actually set aside for risk, not income needed for living expenses. No fraction eliminates drawdowns or guarantees a profit.
Examples are hypothetical and rounded. These calculators explain arithmetic; they do not establish a model’s accuracy or guarantee an outcome.