Free tools
Kelly Calculator
Size a wager from the offered price, the fair odds or probability, and your bankroll.
Free, no account needed. Informational, not betting advice. 21+.
Kelly fraction
Results
- Recommended wager
- $20.83
- Share of bankroll
- 2.08%
- Profit if it wins
- +$25.00
- Edge
- +10.00%
- Full Kelly
- 8.33%
How it works
The full Kelly fraction is edge divided by net odds: fair probability × decimal price − 1, all divided by decimal price − 1. Multiply by the bankroll for the wager. Half, quarter and eighth Kelly scale that down to trade some growth for smaller swings. When the edge is zero or negative the stake is $0.
Worked example
+120 at a fair 50% on a $1,000 bankroll: the edge is +10% and the net odds are 1.20, so full Kelly is 8.33%, or $83.33. Quarter Kelly is $20.83, which would win $25.00.
When to use it
After a check tells you a price beats the fair market, the question is how much to risk. Enter the fair probability from the check or a devigged line and choose a fraction. Most bettors use a quarter or less because their probabilities are estimates.
Questions
Why is the stake $0?
Kelly only bets when the price beats the fair probability. At or below fair, the formula says do not bet, so the tool shows $0 instead of a negative number.
Which fraction should I use?
Full Kelly assumes your probability is exact and tolerates large drawdowns. Half and quarter are common compromises. Eighth suits noisy estimates or correlated bets. Smaller is safer: betting less than Kelly costs growth, betting more costs the bankroll.
Why the caution above a 10% edge?
Edges that large are rare on priced markets. They usually mean the fair probability is too high or the line has already moved. Check the number before you size to it.
Does bankroll mean everything I have?
No. It is the amount set aside for betting that you can afford to lose. Never size from money needed for rent, bills or savings.
Can I enter fair odds instead of a probability?
Yes. Switch the fair number to Fair odds and type the no-vig price. The tool converts it to a probability.
Is this betting advice?
No. The tool is arithmetic on the numbers you type. EdgeFast is informational price discovery, not a sportsbook, and you decide whether to bet. 21+ only.
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Informational, not betting advice. 21+.