Download the appBy Outlier · Updated
About the Kelly Criterion Calculator
The Kelly Criterion uses your odds and estimated win chance to suggest how much of your betting funds to stake. Fractional Kelly uses a smaller share of that amount.
How to use this calculator
- Enter your bankroll: the money you have set aside for betting.
- Enter the offered odds and your estimated win chance.
- Choose full Kelly, a smaller share such as quarter Kelly, or a custom multiplier.
- Read the suggested stake. Check the table to see how errors in your win estimate could change it.
Formula and definitions
- Full Kelly share = (p × d − 1) ÷ (d − 1). Use zero if this result is negative.
- Stake = bankroll × full Kelly share × multiplier.
- p
- Your estimated win chance as a decimal. A 55% chance is 0.55.
- d
- The offered decimal odds. +100 is 2.00.
- Bankroll
- The money you have set aside for betting.
- Multiplier
- The share of full Kelly to use. Quarter Kelly is 0.25.
Worked example
- Start with a $1,000 bankroll, +100 odds, and a 55% win estimate.
- Full Kelly = (0.55 × 2 − 1) ÷ (2 − 1) = 0.10, or 10%.
- Full Kelly gives a $100 stake. Quarter Kelly gives $100 × 0.25 = $25.
- The $25 stake is 2.5% of the bankroll.
How to read your result
The tool returns a $0 stake when expected value is zero or negative. A zero bankroll or multiplier also gives a $0 stake.
A smaller multiplier lowers the amount at risk. It cannot correct a wrong win estimate or make a losing bet profitable.
Assumptions and limitations
- Kelly assumes accurate win estimates and repeated bets. Full Kelly can lead to large losses along the way.
- Bets placed at the same time draw on the same bankroll. Linked bets also share risk. Sizing each in isolation can risk too much.
- Use only funds you can afford to lose. The result is an educational estimate, not a personal stake recommendation.
Common mistake to avoid
A 0.25 multiplier means one quarter of the full Kelly stake. It does not mean betting 25% of your bankroll.
Put your result to work
Try a related calculator, or read our sports betting strategy guides to learn more.
- Expected Value Calculator — Average profit or loss
- No-Vig Fair Odds Calculator — Odds without sportsbook margin
- Implied Probability Calculator — Break-even win chance
Kelly Criterion FAQs
What is quarter Kelly?
Quarter Kelly uses 25% of the full Kelly stake. If full Kelly is $100, quarter Kelly is $25.
Why does Kelly recommend a zero stake?
Your estimated win chance is at or below the break-even chance for those odds. The formula returns $0 because the bet has no positive expected value.
How results are calculated
Results use the formulas and assumptions above. Money is rounded to cents. Odds and percentages are rounded to make them easier to read.
The calculator uses the odds and win chances you enter. It does not load live odds.
J. L. Kelly Jr.: A New Interpretation of Information Rate (1956)