Kelly Criterion
Kelly Criterion Calculator: What Percentage of Your Bankroll to Bet
The Kelly criterion calculator turns your estimated win probability, the odds and your bankroll into the stake that grows a bankroll fastest over the long run. The formula is f* = ((odds − 1) × p − (1 − p)) ÷ (odds − 1). If your probability beats the implied probability of the price, f* is positive and the bet has an edge; if f* is zero or negative, skip it. Because full Kelly swings hard, the calculator also shows half and quarter Kelly stakes.
Kelly Criterion Calculator
Kelly CriterionWhat percentage of your bankroll to stake, with half and quarter Kelly
f* = ((b × p) − q) ÷ bb = decimal odds − 1 (net odds), p = your estimated win probability, q = 1 − p. Stake = bankroll × f*.
How to use the Kelly criterion calculator
Start with your win probability for the game, then enter the price in decimal form (-105 is 1.95; the Odds Converter handles American odds) and your total bankroll. The calculator first converts the odds to an implied probability (1 ÷ odds), subtracts it from your estimate to get your edge, then runs the formula to produce a fraction and a dollar stake.
The win probability does most of the work here. It should not be a hunch; it is your read on form, injuries and line movement. If you use a Mysports.AI model projection, enter the model's probability directly. Overestimate it and the Kelly criterion will tell you to bet too much, which is the most common mistake new bettors make with this formula.
Think in units. One unit is usually 1% of your bankroll, so a $2,000 bankroll makes a $20 unit, and bets above five units are rarely advisable. The calculator rounds stakes to the dollar; if the suggested stake is a small fraction of a unit, the edge is too thin or the bankroll too small, and passing is the better play.
Half Kelly and quarter Kelly: why most bettors skip full Kelly
Full Kelly maximizes bankroll growth on paper, but only if your win probability is exactly right. In practice every estimate carries some error, and that error pushes full Kelly stakes too high, so the swings get brutal: a short losing streak can draw down 30% to 40%.
Half Kelly cuts the stake in half. Pinnacle's simulations found that halving Kelly stakes halves the chance of losing 20% of your bankroll while the median return is only about one quarter lower. Quarter Kelly is more conservative still and suits bettors who are still building a track record. Half, quarter and eighth Kelly are all common choices; the calculator lists them so you can pick with the numbers in front of you.
Kelly criterion limits: bet limits, units and correlated bets
The Kelly criterion assumes you can size a bet freely, but sportsbooks set minimums and maximums, and a small bankroll often gets pinned at the minimum. When that happens, do not force the bet; play only the spots where your edge is clearest.
Kelly is also built for one bet at a time. Betting several games in one afternoon, or a parlay, means the bets share the same bankroll and can be correlated, so total exposure should come down. A common rule of thumb is to keep all open bets combined at no more than 10% to 15% of the bankroll.
Example: 55% win probability, -105 (1.95), $2,000 bankroll
- Implied probability = 1 ÷ 1.95 = 51.3%. Your 55% estimate is 3.7 points higher than the market, so there is an edge.
- Net odds b = 1.95 − 1 = 0.95; f* = (0.95 × 0.55 − 0.45) ÷ 0.95 = 0.0763, a full Kelly fraction of 7.6%.
- Full Kelly stake = $2,000 × 7.6% ≈ $153; half Kelly ≈ $76; quarter Kelly ≈ $38 (all rounded to the dollar).
At half Kelly you would bet about $76, just under four units. Drop the win probability to 52% and f* falls to 1.5%, leaving a half Kelly stake of roughly $15. A three-point difference in the estimate changes the stake fivefold, which is why the probability input deserves most of your attention.
FAQ
What is the Kelly criterion?+
The Kelly criterion is a bankroll management formula published by John L. Kelly in 1956. It uses your win probability and the odds to find the fraction of your bankroll that maximizes long-run growth: a bigger edge means a bigger bet, and no edge means no bet.
How do you calculate half Kelly?+
Run the Kelly formula to get the full Kelly fraction f*, then multiply by 0.5. If f* is 7.6%, half Kelly is 3.8%, which on a $2,000 bankroll is a stake of about $76. Quarter Kelly is f* multiplied by 0.25, or about $38 here.
What does a negative Kelly result mean?+
It means your estimated win probability is below the probability implied by the odds, so the bet has no edge and loses money over time. The Kelly criterion says to skip the bet entirely, not to bet a smaller amount.
Can I use the Kelly criterion on a parlay?+
Yes. Enter the parlay's total decimal odds as the price and your estimate of the chance every leg hits as the win probability. Because that combined probability is usually low, the fraction comes out small, which is Kelly's way of flagging how much risk a parlay carries.
What if the Kelly stake is less than one unit?+
A stake well below one unit (1% of bankroll) means the edge or the bankroll is too small to justify the bet. Pass rather than round up, or build a longer bet log first to confirm your win-probability estimates before moving up from quarter Kelly to half Kelly.
Related calculators
Expected Value Calculator
Expected Value
The one number that says whether a bet wins or loses over time
Open calculator →Implied Probability Calculator
Implied Probability
Convert odds into the market's win probability and find the side with value
Open calculator →Parlay Calculator
Parlay
Parlay odds, payout, profit and the chance every leg hits
Open calculator →Done calculating? See how the AI reads today’s games
A calculator answers the formula; the AI answers the game. Mysports.AI compares model win probability against market odds every day and flags the prices that look mispriced.
For informational purposes only. Sports betting is legal in 39 states and D.C.; rules and minimum age vary by state. 21+. Gambling problem? Call 1-800-GAMBLER.
Odds and vig conventions follow standard US sportsbook pricing (-110 on spreads and totals). The tax line is based on IRS Topic 419 and the Form W-2G instructions (rev. 01/2026); it is not tax advice.