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Compare full and fractional Kelly to see how your probability estimate and odds translate into a stake and share of your bankroll.
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Fill in bankroll, decimal odds, and estimated probability. The initial scenario uses 25% Kelly to show the effect of fractioning.
The Kelly Betting Calculator estimates the theoretical fraction of the bankroll based on three pieces of information: bankroll, decimal odds, and estimated probability. When the calculation finds a positive fraction, it shows the corresponding mathematical value. When the odds do not pay enough for the probability entered, the calculated fraction is zero.
The Kelly criterion compares the reward of the odds with its estimated probability. If the estimated probability exceeds the price implied in the odds, the formula returns a positive fraction of the bankroll. If it does not, the calculated fraction stays at 0%.
The Kelly criterion is a bankroll management formula that calculates the theoretical fraction associated with the difference between the estimated probability and the odds offered.
b = decimal odds - 1p = estimated probabilityq = 1 - pFull Kelly = (b × p - q) ÷ bEquivalent form: full Kelly = ((odds × p) - 1) ÷ (odds - 1)Fractional Kelly = full Kelly × multiplierTheoretical value = bankroll × fractional KellyImplied probability = 1 ÷ decimal oddsFair odds = 1 ÷ estimated probabilityEV = (estimated probability × odds) - 1Edge = estimated probability - implied probabilityImagine a Brasileirão match where your model estimates a 52% chance for the home team and the best available odd is 2.05. With a bankroll of $1,000 and fractional Kelly at 25%, the tool shows positive EV, positive edge, and a smaller stake than full Kelly.
Probability: 52% Odds: 2.05 Implied probability: 48.78% Edge: +3.22 p.p. EV: +6.60% Full Kelly: approximately 6.29% of bankroll 25% Kelly: approximately 1.57% of bankroll Corresponding theoretical value: approximately $15.70| Outcome | Reading |
|---|---|
| Negative or zero Kelly | The calculated fraction is zero: the odds do not pay enough for the estimated probability. |
| Low Kelly | Shows the calculated stake as a smaller share of bankroll. |
| High Kelly | Compare this stake with a smaller Kelly fraction to see how exposure changes. |
| Full Kelly | Full Kelly produces the largest stake under the same inputs. Compare fractional Kelly to explore smaller exposures. |
| Fractional Kelly | Mathematically reduces the fraction and exposure compared to full Kelly. |
Full Kelly uses the full fraction from the formula. In football betting, a slightly optimistic probability can generate a high fraction. Fractional Kelly multiplies that result by 25%, 50%, or 75%; the tool uses 25% only as an initial comparison scenario.
Use Kelly to compare stake sizes, EV to evaluate price, and match factors to examine the probability estimate. Together they give you a fuller view of the scenario.
It is a bankroll management formula that calculates a theoretical fraction based on the estimated probability and the odds entered.
It works as a mathematical exposure ruler when probability and odds belong to the same market and the same line.
It is calculating a portion of full Kelly, such as 25% or 50%, producing a smaller fraction and exposure.
Full Kelly produces the full fraction from the formula; fractional Kelly multiplies that fraction by 25%, 50%, or 75%. The tool uses 25% only as an initial scenario.
It means that, based on the probability entered, the odds do not have enough price. The calculated fraction stays at 0%.
Kelly responds directly to your probability estimate. Compare several estimates to see how sensitive the calculated stake is to that input.
The result shows a stake and share of bankroll calculated from your inputs. Compare full and fractional Kelly, then change the probability estimate to explore sensitivity.
Predora.si organizes football matches with Active Model, Upcoming EV+ Matches, and Odds Comparison.
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