2.40
decimal odds
$1,000 balance
49%
51%
0%
1/99
win
lose
push
round · easy
History
Odds format
Challenge
Betting input
$0
final balance
– median k
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total won
avg k win
largest
streak
rounds won
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total lost
avg k lost
largest
streak
rounds lost
Kelly scores
Outcomes
History
The Kelly Criterion
Definition
Bet the fraction of bankroll that maximizes the long-run growth rate of your money — the size that compounds an edge fastest without ever risking ruin. It scales with the edge and shrinks with the odds; with no edge, it is zero.
f* = pwin · odds − plose odds · (pwin + plose)
Too little You give up growth but keep the ride smooth: half the Kelly bet still captures three quarters of the growth at half the volatility.
Too much Variance outruns the edge. Growth falls faster than it rose, and past roughly twice the Kelly bet a winning proposition compounds against you.
In practice The real world is not a perfect-information game — the probabilities in the formula are your estimates, and the curve punishes overestimating an edge far more than underestimating one. Professionals bet a fixed fraction of full Kelly (half is common), and treat any bet they cannot size with confidence as a pass.
Scoring
The game grades every round with k, your bet divided by that round's Kelly bet: a pass scores 0, the optimal bet scores 1, a bet into a negative edge scores below 0, and anything past 2 is in the region where growth turns negative. The end-of-game charts bucket your k's — a tight cluster around 1, with passes on the trap rounds, is the mark of a disciplined bettor.
Calculator
Growth per round across every bet size, 0–100% of bankroll. The blue dot is the Kelly bet; past the red intercept the same edge loses money.