Calculators
Kelly Criterion Calculator
Knowing a bet is +EV is one thing. Knowing how much to stake on it is another. The Kelly Criterion calculator solves the second problem by working out the exact percentage of your bankroll to wager on any bet based on your edge, so you grow your bankroll as efficiently as possible without taking on unnecessary risk.
Kelly Criterion Calculator
Find your mathematically optimal stake based on your edge, bankroll, and the bookmaker's odds. Maximises long-term growth while controlling for risk of ruin.
What is the Kelly Criterion?
The Kelly Criterion is a mathematical formula that tells you the optimal fraction of your bankroll to bet on any given wager. It was developed by mathematician John L. Kelly Jr. in 1956 and has since become a standard tool in professional sports betting and investment management.
The idea is simply: if you bet too little on a strong edge, you leave money on the table, and if you bet too much, a losing run can wipe out your bankroll. The Kelly Criterion finds the mathematically optimal point between the two, sizing each bet in proportion to your edge over the bookmaker.
It only works on +EV bets. If a bet has no edge, the formula returns zero, meaning don't bet. If it's negative EV, it returns a negative number, still meaning the same thing.
How Is the Kelly Criterion Calculated?
The Kelly formula is:
Kelly % = (b × p - q) ÷ b
Where:
b = Decimal Odds - 1
p = Fair Win Probability (1 ÷ Fair Odds)
q = Fair Loss Probability (1 - p)
Example:
You want to bet on Manchester City to win. Your bookmaker is offering odds of 2.20 and the fair odds from a no-vig calculator are 2.00.
Start by working out each variable:
b = 2.20 - 1 = 1.20
p = 1 ÷ 2.00 = 0.50
q = 1 - 0.50 = 0.50
Now put them into the formula:
Kelly % = (1.20 × 0.50 - 0.50) ÷ 1.20
= (0.60 - 0.50) ÷ 1.20 Kelly %
= 0.10 ÷ 1.20 = 0.0833 OR 8.33%
On a $1,000 bankroll, the recommended stake is 8.33% of $1,000, which amounts to $83.33.
Note that the EV on the bet is 10%, meaning for every dollar wagered, you can expect to profit 10 cents on average over time.
How to Use the Kelly Criterion Calculator
The Kelly betting calculator takes four inputs:
Kelly Multiplier: Scales how aggressive your staking is. The default is 1 (Full Kelly). Lower values reduce stake size and risk
Bankroll: Your total available betting funds
Odds: The decimal odds on offer at your bookmaker
Fair Odds: the no-vig fair odds for the same outcome
Enter all four and the Kelly calculator returns your recommended stake in dollars based on your edge and bankroll size.
Using the example above:
Kelly Multiplier: 1
Bankroll: $1,000
Odds: 2.20
Fair Odds: 2.00
The recommended amount to bet is $83.33, the fraction of bankroll to bet is 8.33% and the EV is 10%.
If the multiplier is set to 0.5 (Half Kelly), the recommended stake drops to $41.67, which is half the full Kelly amount, with much less variance.
Kelly Multiplier Explained
The Kelly Multiplier controls how much of the recommended Kelly stake you actually place. It's the most important setting in the Kelly criterion betting calculator for managing risk.
Full Kelly maximises long-term bankroll growth in theory, but it assumes your edge estimate is perfectly accurate. In practice, win probability estimates are never exact, which means Full Kelly can lead to large swings.
Half Kelly is the most widely recommended setting among professional bettors. It reduces variance while still capturing most of the long-term growth. For most bettors using the Kelly Criterion sports betting calculator, starting at 0.5 is the safer and more sustainable approach.
The lower you set the multiplier, the more conservative your staking becomes. A multiplier of 0.25 or lower is common when a bettor is less confident in their edge estimate or is working with a larger bankroll where preservation is more important than fast growth.
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