Fractional Kelly Calculator

What this page can answer

For this market, the calculator asks whether the entered data can reduce the full Kelly recommendation to a selected fraction. On this page, a market comparison still requires an available price for the identical selection and period.

Sizing reacts sharply to probability error, correlated wagers, and repeatability assumptions.

Reading the formula

The recommendation follows a policy under the entered odds and win rate.

Fractional sizing or a cap can reduce sensitivity to error.

Within this calculation, use a separate scenario for a plausible upper or lower assumption.

Input scope and units

• For fractional Kelly stake, Bankroll represents current betting bankroll.
• In the current scenario, use a current source for Estimated win probability. Here it means your probability estimate.
• American odds records enter positive or negative American odds.
• Keep Kelly fraction to use on the event basis defined here: share of the full Kelly recommendation.

When using the result, inputs collected on different dates may describe states that never existed together.

• Lower estimated win probability before accepting the stake or growth path.
• Compare the baseline with a capped or fractional policy.
• A longer losing-sequence case provides a cautious boundary.

Conditions to review

A personal exposure cap can be lower than the mathematical stake.

In this model, cash, restricted credit, gross return, and net profit may require separate accounting.

For the selected event, use an executable price for the exact selection and stake, not an earlier screenshot or an unavailable best quote.

After documenting fractional Kelly stake, the Kelly Criterion can answer another question.

As a practical check, these numbers demonstrate how fields flow into the answer.

For the Fractional Kelly Calculator, this independent example exists to verify the arithmetic. For this comparison, its inputs are illustrative rather than a forecast for a current event.

Bankroll is set to $940 for this worked case.

Estimated win probability is set to 61.6% for this worked case.

American odds is set to -100 for this worked case.

Kelly fraction to use is set to 26% for this worked case.

Applying the Fractional Kelly rule: stake = bankroll × full Kelly fraction × selected fraction.

• Full Kelly fraction: 23.20%
• Applied fraction: 26.00%
• Estimated edge: 23.20%

For this fractional Kelly stake example, keep the unrounded example inputs until the calculation matches, then apply the same unit checks to current data.

At this stage, inspect units before changing the formula when results differ.

Using the result cautiously

Sizing assumes the edge persists across comparable opportunities.

Personal limits remain outside the optimum.

For the saved case, use the output as decision support and keep personal limits outside it.

The Dutching handles a different calculation and should open as a new case.

When to update the page

When using the result, retain baseline and cautious cases when Bankroll remains uncertain.

In the current scenario, preserve the first answer when Kelly fraction to use changes.

Within this calculation, another reader should be able to repeat the calculation.

Reasons to calculate again

• A smaller fraction reduces volatility but cannot correct a poor probability estimate.
• On this page, review promotion terms, limits, push treatment, void rules, and whether stake is returned before comparing profit.
• For this comparison, a value from another event may use the correct unit while answering a different question.

Input and settlement questions