Model │ Math · Free tool
Kelly Stake
The Kelly criterion sizes a bet to the edge. More when the edge is real, less when it is thin, nothing when it is gone. Set your numbers and see the stake the math actually supports.
A percentage above 0 and below 100.
A price in any format, +120, 1.91 or 10/11.
A dollar amount greater than zero.
The headline figure is half-Kelly, the size most bettors should use.
- Full-Kelly fraction ,
- Full-Kelly stake ,
- Quarter-Kelly stake ,
- Your edge ,
Size the bet to the edge
Bet too big and a cold streak ends the bankroll. Bet too small and a real edge barely compounds. Kelly is the stake that maximises long-run growth, from your win probability and the price.
- Full-Kelly fraction
- The share of the bankroll Kelly says to stake. It scales with the edge: no edge, no bet, the fraction falls to zero or below.
- Half and quarter Kelly
- Full Kelly assumes your probability is exactly right. It never is. Betting a half or a quarter of it keeps most of the growth while cutting the swings sharply, the standard practice for real money.
- Your edge
- Your probability minus the price's break-even probability. Kelly is only meaningful when this is genuinely positive; a negative edge returns a negative fraction, which simply means do not bet.
Kelly is unforgiving of optimism. Overstate your probability and it will hand you a stake far too large, the headline figure is only ever as honest as the number you typed above it.