Enter the price
Use the odds at the book where you plan to bet, not the consensus line.
Kelly criterion calculator
Enter the price and your honest win probability. The calculator shows your edge, the expected value of the bet, and the share of your bankroll the Kelly criterion says to stake.
No number of your own? The no-vig calculator turns a sharp line into a fair win probability.
Kelly fraction
Your stake
Quarter Kelly$13.751.38% of your bankroll
Edge+2.62 pts
Expected value+5.00%
Break-even win rate52.38%
Full Kelly5.50%
Edge found. Quarter Kelly stakes $13.75, or 1.38% of your bankroll. Expected profit is $5.00 per $100 staked.
Kelly sizes one bet at a time. A negative result shows as zero, never as a bet on the other side.
How it works, the math and FAQ
How to use the calculator
Price, probability, fraction
Enter your win probability
Use a model, a projection or the fair price from a sharp book. Kelly treats your estimate as fact, so an inflated number means an oversized bet.
Pick a fraction
Quarter and half Kelly are the usual choices. A smaller fraction trades a little growth for much smaller swings.
Full or fractional
Why most bettors use fractional Kelly
Full Kelly gives the fastest long-run bankroll growth when your probability is exact. Real estimates carry error. Overrate every edge by double and you stake twice the Kelly amount, which grows a bankroll at close to zero over time.
Half Kelly keeps about three quarters of the growth with half the variance. Quarter Kelly suits a new model or a short record. Size down further for props and longshots, where your probability estimate carries the most error.
The formula
How the Kelly stake works
b = decimal odds - 1
p = your win probability, q = 1 - p
f* = (b × p - q) / b
stake = f* × fraction × bankroll
f* at or below zero means no bet
Example: 55% at -110, $1,000 bankroll
- b = 1.909 - 1 = 0.909
- f* = (0.909 × 0.55 - 0.45) / 0.909 = 5.5%
- Quarter Kelly: 5.5% × 0.25 = 1.375%
- Stake: $1,000 × 1.375% = $13.75
FAQ
Common questions
What is the Kelly criterion?
A formula for bet size. Kelly stakes a share of your bankroll in proportion to your edge, which maximizes long-run growth. The formula is f = (bp - q) / b, with b as decimal odds minus 1, p as your win probability and q as 1 - p.
Why does the calculator say to bet nothing?
Your win probability sits at or below the break-even rate for the price. With no edge, Kelly returns zero. A zero never means to bet the other side. Run the other side through the calculator at its own price.
Should I use full Kelly or fractional Kelly?
Fractional. Full Kelly assumes a perfect probability and produces deep drawdowns even then. Quarter Kelly is a common default. Move toward half Kelly once a long record shows your edges hold up.
How does Kelly handle several bets at once?
The single-bet formula assumes one bet at a time. For several bets on the same night, size each one, then scale every stake down by the same factor if the total runs past your usual daily exposure.
Where does my win probability come from?
From a model, a projection, or the fair price from a sharp book. The no-vig calculator turns a sharp two-way line into a fair probability to enter here.
The Kennel
Read the math in depth
Let the bots find the edge for you.
5 days free, then $7 a week plus Winible's service fee. Renews weekly until you cancel.